Book

Chapter 1: Introduction to Computers, Programs, and Java

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1.1 Introduction

• Programming = creating software (set of instructions for a computer).

• Software is everywhere: from PCs to mobile devices to appliances.

• Learning one language (like Java) helps you transition to others; the core idea is problem-solving using a programming approach.

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1.2 What is a Computer?

• Computer: Electronic device that processes and stores data using hardware + software.

• Hardware: Physical components (CPU, memory, storage, input/output devices).

• Software: Invisible instructions controlling hardware (apps, OS, etc.).

• CPU (Central Processing Unit):

  • "Brain" of the computer.

  • Executes instructions from memory.

  • Components: Control Unit + Arithmetic/Logic Unit.

  • Measured in GHz (e.g., 3 GHz = 3 billion pulses/sec).

  • Multicore CPUs enable parallel processing.

• Bits and Bytes:

  • Bit = 0 or 1 (binary digit), smallest data unit.

  • Byte = 8 bits.

• Memory (RAM):

  • Volatile storage for data/instructions.

  • Each byte has a unique address.

• Storage Devices:

  • Non-volatile (e.g., hard disks, SSDs, USBs, CDs).

  • Used to permanently store data and programs.

• Input/Output Devices: Keyboard, mouse, monitor, printer, etc.

• Communication Devices: Modems, network cards, Wi-Fi adapters.

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1.3 Programming Languages

• Types:

  1. Machine Language: Native binary code (hard to read).

  2. Assembly Language: Uses mnemonics like add, sub.

     • Needs an assembler.

  3. High-Level Language (e.g., Java, Python, C++):

     • English-like, platform-independent.

     • Needs a compiler or interpreter.

• Source Program: Code written in a high-level language.

• Compiler: Translates entire source code into machine code (e.g., javac).

• Interpreter: Translates and executes one line at a time.

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1.4 Operating Systems

• Manages hardware/software.

• Examples: Windows, macOS, Linux.

• Responsibilities:

  • Control hardware.

  • Allocate resources.

  • Schedule operations (multiprogramming, multithreading).

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1.5 Java, the World Wide Web, and Beyond

• Java was designed to be:

  • Platform-independent: “Write once, run anywhere.”

  • Used for: Web applications, Android apps, server-side development.

• Applets: Java programs that run in a browser (now largely deprecated).

• Java is used for Web, mobile, desktop, and embedded systems.

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1.6 Java Language Specification, API, JDK, and IDE

• Java Language Specification: Syntax and semantics rules.

• API (Application Programming Interface): Predefined Java classes and libraries.

• JDK (Java Development Kit): Contains compiler, debugger, JVM.

• IDE (e.g., Eclipse, NetBeans): Tools for code writing, debugging, and compiling.

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1.7 A Simple Java Program

public class Welcome {
    public static void main(String[] args) {
        System.out.println("Welcome to Java!");
    }
}

• main(): Entry point of a Java application.

• Java is case-sensitive.

• Every statement ends with ;.

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1.8 Creating, Compiling, and Executing a Java Program

• Save code in a .java file.

• Compile using: javac FileName.java → creates .class bytecode.

• Run using: java ClassName.

• Java uses JVM to execute bytecode on any OS.

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1.9 Displaying Text in a Message Dialog Box

• Use JOptionPane from javax.swing:

import javax.swing.JOptionPane;
JOptionPane.showMessageDialog(null, "Welcome to Java!");

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1.10 Programming Style and Documentation

• Good Practices:

  • Use indentation.

  • Add comments (// or /* */).

  • Use meaningful names.

• Comments are ignored by the compiler but improve code readability.

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1.11 Programming Errors

• Syntax Errors: Grammar mistakes (e.g., missing ;).

• Runtime Errors: Occur during execution (e.g., divide by zero).

• Logic Errors: Program runs but gives incorrect output due to flawed logic.

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✅ Key Terms Summary

• Bit, Byte, CPU, RAM, Compiler, Interpreter, JDK, JVM, API, etc.

• Learn distinctions: low-level vs high-level languages, source vs bytecode, OS vs application software.

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Chapter 2: Elementary Programming

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📘 Chapter 2: Elementary Programming

This chapter introduces the fundamental building blocks of Java programming, focusing on writing programs that perform basic computations, process input, and display output.

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2.1 Introduction

• You move beyond printing simple messages to writing meaningful programs that solve real-world problems (e.g., computing loan payments).

• Key skills:

  • Data storage (variables)

  • Computation (expressions)

  • Input/output handling

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2.2 Writing a Simple Program

• Programs solve problems using algorithms (step-by-step solutions).

• Typical program development involves:

  1. Understand the problem.

  2. Design an algorithm.

  3. Translate it into code.

• Example: Area of a circle.

  area = radius * radius * π;

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2.3 Reading Input from the Console

• Java uses the Scanner class for input.

  import java.util.Scanner;
  Scanner input = new Scanner(System.in);
  double radius = input.nextDouble();

• Console input allows interaction with users.

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2.4 Identifiers

• Identifiers are names for variables, methods, classes, etc.

• Rules:

  • Can include letters, digits, _, $.

  • Cannot start with a digit.

  • Cannot be a Java keyword (like int, class).

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2.5 Variables

• Used to store data in a program.

  int age = 25;
  double area;

• Must be declared before use.

• Can be updated:

  area = radius * radius * 3.14159;

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2.6 Assignment Statements and Expressions

• Use = to assign values:

  x = 5;
  y = x + 2;

• Right-hand side is evaluated first.

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2.7 Named Constants

• Constant values are declared using final.

  final double PI = 3.14159;

• Constants improve readability and maintenance.

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2.8 Naming Conventions

• Classes: Capitalize each word (e.g., ComputeArea).

• Variables and methods: start lowercase, use camelCase (e.g., area, computeArea).

• Constants: ALL_CAPS (e.g., PI, MAX_SPEED).

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2.9 Numeric Data Types and Operations

• Java supports six numeric types:

  • Integer: byte, short, int, long

  • Floating point: float, double

• Arithmetic operators:

  • +, -, *, /, % (modulus)

  • Math.pow(a, b) for exponentiation

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2.10 Numeric Literals

• int, long (suffix L), float (suffix F), double

• Scientific notation: 1.23e2 = 123.0

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2.11 Evaluating Expressions and Operator Precedence

• Follow standard precedence rules:

  • *, /, % > +, -

• Parentheses can change precedence.

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2.12 Case Study: Displaying the Current Time

• Use System.currentTimeMillis() to get milliseconds since Jan 1, 1970.

• Calculate hours, minutes, seconds using division and modulus.

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2.13 Augmented Assignment Operators

• Shorthand:

  x += 1; // same as x = x + 1;
  x *= 2;

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2.14 Increment and Decrement Operators

• ++ and --

  • Pre: ++x (increment first)

  • Post: x++ (use then increment)

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2.15 Numeric Type Conversions

• Widening (safe): int → double

• Narrowing (may lose data): must use casting

  int x = (int) 3.14;

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2.16 Software Development Process

Five steps:

1. Problem definition

2. Algorithm design

3. Code implementation

4. Testing and debugging

5. Maintenance

Case study: Loan calculator

monthlyPayment = loanAmount * monthlyInterestRate /
                 (1 - 1 / Math.pow(1 + monthlyInterestRate, numberOfYears * 12));

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2.17 Character Data Type and Operations

• Use char to represent a single character:

  char letter = 'A';

• Each char is a Unicode number.

• int and char are compatible (e.g., 'A' + 1 = 'B').

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2.18 The String Type

• A String is a sequence of characters (not a primitive).

  String name = "John";

• Common methods:

  • length()

  • toLowerCase(), toUpperCase()

  • charAt(i), concat()

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2.19 Getting Input from Input Dialogs

• Uses JOptionPane for GUI-based input/output:

  String name = JOptionPane.showInputDialog("Enter your name");

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✅ Summary Table

Concept	Example	Notes
Variable Declaration	int count;	Must declare before use
Constant	final double PI = 3.14;	Value cannot change
Input (Console)	Scanner input = new Scanner(System.in);	Use nextInt(), nextDouble()
Input (GUI)	JOptionPane.showInputDialog(...)	String returned
Math	Math.pow(x, y)	For exponents
Char → Int	int code = 'A';	Outputs 65
Casting	(int) 3.5 → 3	Converts to integer
Operators	+ - * / %	Standard math ops

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Here are the detailed notes for Chapter 3: Selections from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

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📘 Chapter 3: Selections

This chapter introduces how to make decisions in Java programs using selection (conditional) statements such as if, if-else, switch, and logical operators.

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3.1 Introduction

• Sometimes a program needs to make decisions (e.g., only compute area if radius ≥ 0).

• Java provides selection statements to control program flow based on conditions.

• Conditions use Boolean expressions that evaluate to true or false.

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3.2 boolean Data Type

• Declares variables that hold true or false.

  boolean isValid = true;

• Comparison Operators:

  • <, <=, >, >=, ==, !=

  • Example:

    if (radius >= 0)

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3.3 if Statements

• One-way selection:

  if (score >= 60)
      System.out.println("Passed");

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3.4 Case Study: Guessing Birthdays

• Demonstrates using if to accumulate a guessed date based on user input.

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3.5 Two-Way if-else Statements

• Provides two branches:

  if (x > 0)
      System.out.println("Positive");
  else
      System.out.println("Zero or negative");

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3.6 Nested and Multi-Way if-else

• Multiple levels of conditions:

  if (score >= 90)
      grade = 'A';
  else if (score >= 80)
      grade = 'B';
  // etc.

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3.7 Common Errors

• Dangling else problem: Always pair else with nearest unmatched if.

• Use braces {} to avoid ambiguity and logic errors.

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3.8 Generating Random Numbers

• Use Math.random():

  int number = (int)(Math.random() * 10);

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3.9 Case Study: BMI Calculator

• Compute BMI using:

  bmi = weight / (height * height);

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3.10 Case Study: Tax Calculator

• Multi-way branching based on income and filing status.

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3.11 Logical Operators

• Combine conditions:

  • && (AND), || (OR), ! (NOT)

  if (x > 0 && x < 100)

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3.12 Case Study: Leap Year

• Leap year condition:

  if ((year % 4 == 0 && year % 100 != 0) || year % 400 == 0)

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3.13 Case Study: Lottery Game

• Compares generated and user input digits using selection and logic.

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3.14 switch Statements

• Useful for discrete choices:

  switch (grade) {
      case 'A': ...
      case 'B': ...
      default: ...
  }

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3.15 Conditional (Ternary) Operator

• Shorthand for if-else:

  result = (x > 0) ? "Positive" : "Non-positive";

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3.16 Formatting Output

• Use System.out.printf for formatted output:

  System.out.printf("Age: %d, GPA: %.2f", age, gpa);

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3.17 Operator Precedence and Associativity

• Precedence: *, /, % > +, - > comparison > logical

• Use parentheses to enforce desired order.

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3.18 Confirmation Dialogs

• Use JOptionPane.showConfirmDialog(...) for user decisions:

  int option = JOptionPane.showConfirmDialog(null, "Continue?");

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3.19 Debugging

• Debugging involves:

  • Setting breakpoints

  • Tracing variable values

  • Stepping through code

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✅ Key Concepts Summary

Topic	Description
Boolean type	true or false
Comparison ops	<, >, ==, !=, etc.
Logical ops	&&, `
Control structures	if, if-else, switch, ternary ? :
Random numbers	Math.random()
Formatting	System.out.printf()
Dialogs	JOptionPane for input/output/confirmation

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Here are detailed notes for Chapter 4: Loops from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

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📘 Chapter 4: Loops

Loops are fundamental constructs in programming that allow repeated execution of a set of statements.

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4.1 Introduction

• Loops automate repetitive tasks.

• Example:

  int count = 0;
  while (count < 100) {
      System.out.println("Welcome to Java!");
      count++;
  }

• Loop consists of:

  • Initialization

  • Condition check

  • Loop body

  • Update

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4.2 The while Loop

• Syntax:

  while (condition) {
      // Loop body
  }

• Condition is checked before the loop body.

• Might never execute if condition is initially false.

• Used when repetitions are not known in advance.

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4.2.1–4.2.3 Loop Design Strategy

• Steps:

  1. Identify tasks that repeat.

  2. Determine loop control structure.

  3. Design and test the loop carefully.

• Avoid infinite loops and off-by-one errors.

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4.2.4 Sentinel-Controlled Loops

• A sentinel value ends input:

  int data = input.nextInt();
  while (data != 0) {
      sum += data;
      data = input.nextInt();
  }

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4.2.5 Input Redirection

• Redirect input from a file using < input.txt.

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4.3 The do-while Loop

• Executes loop body once before checking the condition.

• Syntax:

  do {
      // Loop body
  } while (condition);

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4.4 The for Loop

• Syntax:

  for (initialization; condition; update) {
      // Loop body
  }

• Used when number of iterations is known.

• All parts (init, condition, update) are optional.

• Example:

  for (int i = 0; i < 10; i++) {
      System.out.println(i);
  }

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4.5 Which Loop to Use

• Use for when number of iterations is known.

• Use while when condition is pre-evaluated.

• Use do-while when at least one execution is needed.

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4.6 Nested Loops

• A loop inside another loop.

• Commonly used in tables or matrix processing.

• Example: Multiplication table:

  for (int i = 1; i <= 9; i++) {
      for (int j = 1; j <= 9; j++) {
          System.out.printf("%4d", i * j);
      }
      System.out.println();
  }

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4.7 Minimizing Numeric Errors

• Floating-point operations can be imprecise.

• Example: summing from 0.01 to 1.0

  • Summing small to large gives more accurate results than large to small.

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4.8 Case Studies

• GCD Calculation:

  int gcd = 1;
  for (int k = 2; k <= n1 && k <= n2; k++) {
      if (n1 % k == 0 && n2 % k == 0)
          gcd = k;
  }

• Future Tuition Prediction

• Monte Carlo Simulation

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4.9 break and continue

• break: exits the loop immediately.

• continue: skips the current iteration and moves to the next.

• Example:

  for (int i = 0; i < 10; i++) {
      if (i == 5) continue;
      System.out.println(i);
  }

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4.10 Case Study: Prime Numbers

• Checks if a number is divisible only by 1 and itself using loops.

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4.11 Loop Control with Confirmation Dialog

• GUI-based loop control using JOptionPane:

  int option = JOptionPane.YES_OPTION;
  while (option == JOptionPane.YES_OPTION) {
      // input logic
      option = JOptionPane.showConfirmDialog(null, "Continue?");
  }

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✅ Chapter 4 Summary

Concept	Description
while loop	Pretest loop; repeats while condition is true
do-while loop	Posttest loop; always runs at least once
for loop	Pretest; concise form with init, condition, update
Sentinel value	Special input value to terminate loop
Nested loop	Loop inside another loop
break	Terminates the loop early
continue	Skips to next iteration
Numeric precision	Watch for floating-point errors
Dialog-based loops	Uses GUI for flow control

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Here's a concise cheat sheet for Chapter 5: Methods from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

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🧠 Java Methods Cheat Sheet – Chapter 5

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📌 5.1 What is a Method?

• A method is a block of code that performs a specific task.

• Benefits:

  • Reuse code

  • Improve modularity

  • Enhance readability and debugging

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📌 5.2 Defining a Method

public static returnType methodName(parameters) {
    // method body
}

• Example:

public static int max(int num1, int num2) {
    return (num1 > num2) ? num1 : num2;
}

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📌 5.3 Calling a Method

int larger = max(5, 10);

• Must match number, type, and order of arguments.

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📌 5.4 void Method Example

public static void printMessage() {
    System.out.println("Hello!");
}

• Use void when no return value is needed.

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📌 5.5 Passing Parameters by Value

• Java uses pass-by-value for all arguments.

• Primitives: Copy of the value.

• Objects: Copy of the reference (not the actual object).

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📌 5.6 Modularizing Code

• Modularization: Breaking code into smaller, reusable methods.

• Increases code maintainability and clarity.

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📌 5.7 Case Study: Decimal to Hex

• Break the problem into sub-methods:

  • decimalToHex(int decimal)

  • toHexChar(int value)

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📌 5.8 Method Overloading

• Define multiple methods with the same name but different parameter lists.

public static int max(int a, int b)
public static double max(double a, double b)

• Compiler picks the appropriate version based on arguments.

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📌 5.9 Scope of Variables

• Local variable: Declared inside a method or block; not visible outside.

• Global (class-level) variables not used yet (introduced in OOP chapters).

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📌 5.10 The Math Class

• Java's built-in class for common math operations.

Math.pow(x, y);     // exponentiation
Math.sqrt(x);       // square root
Math.random();      // [0.0, 1.0)
Math.abs(x);        // absolute value

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📌 5.11 Case Study: Random Characters

• Uses RandomCharacter class with methods like:

  • getRandomUpperCaseLetter()

  • getRandomDigitCharacter()

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📌 5.12 Method Abstraction & Stepwise Refinement

• Abstraction: Use methods without knowing implementation details.

• Stepwise Refinement: Break down problems into smaller subproblems recursively.

• Think of methods as black boxes:

  • You know what it does, not how it works inside.

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✅ Common Patterns & Syntax

Purpose	Syntax / Example
Define method	public static int sum(int a, int b)
Call method	sum(5, 10)
No return	public static void printHello()
Return statement	return value;
Overloading	Same name, different parameters
Math class	Math.max(x, y)
Random number	(int)(Math.random() * 10)

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🚫 Common Mistakes to Avoid

• Not matching parameter types/number in method call.

• Forgetting return statement for non-void methods.

• Using a variable outside its scope.

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Here’s a Cheat Sheet for Chapter 6: Single-Dimensional Arrays from Introduction to Java Programming (9th Edition) by Y. Daniel Liang:

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🧠 Java Arrays – Chapter 6 Cheat Sheet

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🔹 What is an Array?

• A data structure to store multiple values of the same type.

• Elements are stored in contiguous memory and accessed via an index.

double[] numbers = new double[10];
numbers[0] = 1.5;

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🔹 Declaring & Creating Arrays

int[] scores;                   // Declaration
scores = new int[5];           // Creation
int[] ages = new int[10];      // Combined

• Index starts from 0.

• Access using array[index].

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🔹 Array Initialization

int[] list = {1, 2, 3, 4}; // array initializer

int[] list = new int[5];  // default values: 0 for int, false for boolean, '\u0000' for char

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🔹 Common Array Operations

Task	Example
Input	list[i] = input.nextInt();
Output	System.out.println(list[i]);
Sum	sum += list[i];
Max	if (list[i] > max)
Shuffle	Use Math.random() + swap logic
Shift	Manually copy values to new indices

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🔹 Looping Through Arrays

for (int i = 0; i < list.length; i++) {
    System.out.println(list[i]);
}

🔹 Enhanced for-each Loop

for (int item : list) {
    System.out.println(item);
}

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🔹 Passing Arrays to Methods

public static void printArray(int[] arr) {
    for (int i : arr) System.out.print(i + " ");
}

🔹 Returning Arrays from Methods

public static int[] createArray() {
    int[] arr = {1, 2, 3};
    return arr;
}

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🔹 Variable-Length Argument Lists

public static int sum(int... numbers) {
    int total = 0;
    for (int n : numbers) total += n;
    return total;
}

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🔹 Searching Arrays

• Linear Search:

  for (int i = 0; i < arr.length; i++)
      if (arr[i] == key) return i;

• Binary Search (sorted arrays only):

  Arrays.binarySearch(arr, key);

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🔹 Sorting Arrays

• Selection Sort, Insertion Sort: Manual sorting methods

• Built-in sort:

  Arrays.sort(arr);

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🔹 The java.util.Arrays Class

Arrays.sort(arr);                     // Sort
Arrays.binarySearch(arr, key);       // Search
Arrays.equals(arr1, arr2);           // Compare
Arrays.fill(arr, 5);                 // Fill with value
Arrays.toString(arr);                // Print array

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🔹 Case Studies

• LottoNumbers: Random, unique number selection.

• DeckOfCards: Simulate shuffling and dealing cards.

• Counting Letters: Count occurrences of characters using char[].

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✅ Quick Tips

• Index out of bounds? You’ll get ArrayIndexOutOfBoundsException.

• Array size is fixed once declared.

• Use .length to get array size (e.g., arr.length).

• Off-by-one errors are common—check loop bounds carefully!

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Here's a cheat sheet for Chapter 7: Multidimensional Arrays from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

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🧠 Chapter 7: Multidimensional Arrays – Cheat Sheet

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🔹 Two-Dimensional Arrays (2D Arrays)

✅ Declaration:

int[][] matrix;

✅ Creation:

matrix = new int[3][4]; // 3 rows, 4 columns

✅ Initialization:

int[][] matrix = {
  {1, 2, 3},
  {4, 5, 6},
  {7, 8, 9}
};

✅ Accessing Elements:

matrix[1][2] // 6 (2nd row, 3rd column)

---

🔹 Key Properties

• matrix.length → Number of rows

• matrix[0].length → Number of columns (of first row)

• Java 2D arrays are arrays of arrays (ragged arrays are allowed).

---

🔹 Ragged Arrays

int[][] ragged = new int[3][];
ragged[0] = new int[2];
ragged[1] = new int[4];
ragged[2] = new int[3];

---

🔹 Common Operations

🔸 Input a 2D Array:

for (int i = 0; i < matrix.length; i++)
  for (int j = 0; j < matrix[i].length; j++)
    matrix[i][j] = input.nextInt();

🔸 Print a 2D Array:

for (int[] row : matrix)
  System.out.println(Arrays.toString(row));

🔸 Sum All Elements:

int total = 0;
for (int i = 0; i < matrix.length; i++)
  for (int j = 0; j < matrix[i].length; j++)
    total += matrix[i][j];

🔸 Sum by Column:

for (int col = 0; col < matrix[0].length; col++) {
  int total = 0;
  for (int row = 0; row < matrix.length; row++)
    total += matrix[row][col];
  System.out.println("Sum for column " + col + " is " + total);
}

🔸 Find Row with Maximum Sum:

int maxRow = 0, maxSum = 0;
for (int i = 0; i < matrix.length; i++) {
  int rowSum = Arrays.stream(matrix[i]).sum();
  if (rowSum > maxSum) {
    maxSum = rowSum;
    maxRow = i;
  }
}

🔸 Shuffle Elements:

for (int i = 0; i < matrix.length; i++)
  for (int j = 0; j < matrix[i].length; j++) {
    int i1 = (int)(Math.random() * matrix.length);
    int j1 = (int)(Math.random() * matrix[i].length);
    int temp = matrix[i][j];
    matrix[i][j] = matrix[i1][j1];
    matrix[i1][j1] = temp;
  }

---

🔹 Passing 2D Arrays to Methods

public static void printMatrix(int[][] m) {
  for (int[] row : m)
    System.out.println(Arrays.toString(row));
}

---

🔹 Case Studies

• Grading Multiple-Choice Tests: Rows represent students, columns represent answers.

• Closest Pair of Points: Use 2D array to store coordinates.

• Sudoku Checker: Validate 9×9 matrix with nested loops.

• Weather Analysis: 3D array to track temperature and humidity across time.

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🔹 Multidimensional Arrays (3D and beyond)

✅ Declaration:

int[][][] data = new int[10][24][2];

✅ Example:

data[day][hour][0] = temperature;
data[day][hour][1] = humidity;

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✅ Summary Table

Task	Syntax
Declare 2D array	int[][] m;
Create 2D array	new int[3][4]
Access element	m[i][j]
Iterate rows	for (int i = 0; i < m.length; i++)
Iterate columns	for (int j = 0; j < m[i].length; j++)
Ragged arrays	Rows can have different lengths
3D arrays	int[][][] x = new int[5][4][3]

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Here is a cheat sheet for Chapter 8: Objects and Classes from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

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🧠 Java OOP – Chapter 8: Objects and Classes Cheat Sheet

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🔹 Object-Oriented Programming (OOP) Basics

Term	Description
Object	Instance of a class with state (fields) and behavior (methods)
Class	Template or blueprint to create objects
Instance	An actual object created from a class
Instantiation	The process of creating an object using new

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🔹 Defining a Class

public class Circle {
    double radius = 1.0;

    public Circle() { }

    public Circle(double r) {
        radius = r;
    }

    public double getArea() {
        return radius * radius * Math.PI;
    }

    public void setRadius(double r) {
        radius = r;
    }
}

---

🔹 Creating Objects

Circle c1 = new Circle();         // Default constructor
Circle c2 = new Circle(5.0);      // Overloaded constructor

---

🔹 Accessing Members

• Fields/Methods: objectName.member

System.out.println(c2.getArea());
c2.setRadius(10.0);

---

🔹 Constructors

• Special methods with the same name as the class

• No return type (not even void)

• Used with new to create objects

public Circle() { ... }
public Circle(double r) { ... }

---

🔹 Reference Variables

Circle myCircle = new Circle();

• Stores a reference (memory address) to the object, not the object itself.

---

🔹 UML Class Diagram Format

ClassName
--------------
fieldName: dataType
--------------
methodName(params): returnType

---

🔹 Using Standard Java Classes

• Date: new java.util.Date()

• Random: new java.util.Random()

• JFrame: GUI window class in Swing

---

🔹 Static Members

Static Keyword	Description
static	Shared across all instances
Example:

public static int count;
public static void showCount() { ... }

• Access: ClassName.member or object.member (prefer class style)

---

🔹 Visibility Modifiers

Modifier	Access Level
public	Anywhere
private	Inside the class only
(no modifier)	Package-private

---

🔹 Encapsulation

• Hide data using private fields

• Provide getters/setters to access/update

private double radius;

public double getRadius() { return radius; }
public void setRadius(double r) { radius = r; }

---

🔹 Passing Objects to Methods

• Passes the reference (not copy of object)

• Object data can be changed via methods

---

🔹 Arrays of Objects

Circle[] circles = new Circle[10];
for (int i = 0; i < circles.length; i++) {
    circles[i] = new Circle(Math.random() * 100);
}

---

✅ Summary Table

Concept	Example / Syntax
Define Class	class ClassName { ... }
Create Object	new ClassName()
Access Field	object.field
Call Method	object.method()
Constructor	ClassName(...) { ... }
Static Variable	static int x;
Getter/Setter	getX(), setX()
Reference Variable	ClassName ref = new ClassName();
Array of Objects	ClassName[] arr = new ClassName[n];

---

Here’s a cheat sheet for Chapter 9: Strings and Text I/O from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

---

🧠 Java Strings & Text I/O – Chapter 9 Cheat Sheet

---

🔹 9.1 Introduction

• Java provides String, StringBuilder, and StringBuffer for processing textual data.

• Strings in Java are objects, not arrays of characters like in C.

---

🔹 9.2 The String Class

✅ Creating Strings

String s1 = "Java";
String s2 = new String("Java");
char[] chars = {'J', 'a', 'v', 'a'};
String s3 = new String(chars);

✅ Immutable Strings

• Strings cannot be changed after creation.

String s = "Java";
s = "HTML"; // new object created

✅ Interned Strings

• JVM stores string literals in a common pool.

String s1 = "Java";
String s2 = "Java";
s1 == s2 // true (same reference)

---

🔹 String Operations

Operation	Example
Length	s.length()
Char at index	s.charAt(i)
Substring	s.substring(0, 5)
Concatenation	s1 + s2 or s1.concat(s2)
Comparison	s1.equals(s2) or s1.compareTo(s2)
Replace	s.replace('a', 'b')
Trim spaces	s.trim()
Convert case	s.toLowerCase(), s.toUpperCase()
Split	s.split(" ")

---

🔹 9.3 Palindrome Check

public static boolean isPalindrome(String s) {
  int low = 0, high = s.length() - 1;
  while (low < high) {
    if (s.charAt(low) != s.charAt(high)) return false;
    low++; high--;
  }
  return true;
}

---

🔹 9.4 Hex to Decimal

int decimal = Integer.parseInt("1A", 16);

---

🔹 9.5 The Character Class

Method	Purpose
isLetter(ch)	Check if letter
isDigit(ch)	Check if digit
isUpperCase(ch)	Check uppercase
isLowerCase(ch)	Check lowercase
toUpperCase(ch)	Convert to upper
toLowerCase(ch)	Convert to lower

---

🔹 9.6 StringBuilder and StringBuffer

Feature	StringBuilder	StringBuffer
Mutable?	✅ Yes	✅ Yes
Thread-safe?	❌ No	✅ Yes
Usage

StringBuilder sb = new StringBuilder("Java");
sb.append(" Rocks");

| Common Methods |

sb.append("text");
sb.insert(0, "Hey ");
sb.delete(2, 4);
sb.reverse();
sb.toString();

---

🔹 9.7 Command-Line Arguments

public static void main(String[] args) {
  for (String arg : args)
    System.out.println(arg);
}

---

✅ Summary Table

Feature	Key Points
String	Immutable, used for fixed text
StringBuilder	Mutable, better performance in single-threaded context
StringBuffer	Mutable, thread-safe
Character	Static utility methods for character processing
Command-line args	Passed as String[] args to main()
String methods	length(), charAt(), substring(), indexOf(), etc.

---

Here’s a Cheat Sheet for Chapter 10: Thinking in Objects from Introduction to Java Programming, 9th Edition by Y. Daniel Liang:

---

🧠 Java OOP Deep Dive – Chapter 10: Thinking in Objects

---

🔹 10.1 Introduction

• Moves from procedural to object-oriented thinking.

• Emphasizes class design, encapsulation, composition, and abstraction.

• Promotes modularity, reuse, and maintainability.

---

🔹 10.2 Immutable Objects and Classes

• Immutable object: Once created, state cannot be changed.

• Requirements for immutability:

  • All fields private

  • No setter methods

  • No accessors that expose mutable fields

final class Student {
  private final String name;
  private final Date dateCreated; // make defensive copy
}

---

🔹 10.3 Scope of Variables

• Local variables override instance variables if same name.

• Instance variables are accessible by all instance methods.

• Block scope: A variable declared inside {} is only accessible within that block.

---

🔹 10.4 The this Reference

• Refers to the current object.

• Used when parameter name hides instance variable:

this.name = name;

• Can invoke another constructor:

this(...);

---

🔹 10.5 Class Abstraction & Encapsulation

• Abstraction: Hide internal implementation.

• Encapsulation: Combine data + methods; restrict direct access.

• Only expose a class's contract (public methods/constants).

private double balance;
public double getBalance() { return balance; }

---

🔹 10.6 Procedural vs Object-Oriented Thinking

Procedural	Object-Oriented
Data & methods separate	Data + methods = object
Focus on actions	Focus on entities
Example: BMI calculator in main	Better: Define BMI class

---

🔹 10.7 Object Composition

• Use has-a relationship (composition):

public class Student {
  private Address address;
}

• Good for modularity and reuse.

---

🔹 10.8–10.10 Case Studies

✅ Designing Classes:

• Course Class

• Custom Stack Class

• GuessDate Class

• Focus on:

  • Good encapsulation

  • Real-world modeling

  • Class contracts

---

🔹 10.11 Class Design Guidelines

• One class = one clear responsibility

• Use private for fields

• Provide get/set only when necessary

• Favor composition over inheritance

• Keep class self-contained and reusable

---

🔹 10.12 Wrapper Classes

• Convert primitive types to objects:

  Integer i = Integer.valueOf(5); // Boxing
  int n = i.intValue(); // Unboxing

• Types: Integer, Double, Boolean, etc.

---

🔹 10.13 Autoboxing/Unboxing

Integer i = 10; // autobox
int n = i;      // unbox

• Java automatically wraps/unwraps primitive types.

---

🔹 10.14 BigInteger & BigDecimal

• For arbitrary precision numbers:

BigInteger big = new BigInteger("123456789123456789");
BigDecimal dec = new BigDecimal("3.1415926535");

• Use add, multiply, compareTo, etc.

---

✅ Summary Table

Topic	Key Concept
Immutability	Object’s state can't change
this	Refers to current object
Abstraction	Use object’s public interface only
Encapsulation	Keep details private
Composition	"Has-a" relationship
Wrapper Classes	Object form of primitives
BigInteger / BigDecimal	Use for large or precise values

---

Chapter 11: Inheritance and Polymorphism

---

11.1 Introduction to Inheritance

• Inheritance allows defining a new class based on an existing one.

• The new class is called a subclass (or child class), and the existing one is a superclass (or parent class).

• Promotes code reuse, organization, and modularity.

---

11.2 Superclasses and Subclasses

• A superclass contains common features.

• A subclass extends a superclass and inherits accessible members.

• Example: GeometricObject as a superclass, Circle and Rectangle as subclasses.

• Subclass inherits methods and fields (except constructors and private members).

---

11.3 Using the super Keyword

• super is used to:

  • Call the superclass’s constructor: super(args);

  • Invoke superclass methods: super.methodName();

• The superclass constructor call must be the first statement in a subclass constructor.

---

11.4 Overriding Methods

• A method in a subclass can override a superclass method with the same signature and return type.

• @Override annotation is recommended for clarity and compile-time checking.

• Only accessible (non-private) methods can be overridden.

---

11.5 Overriding vs. Overloading

• Overriding: same method name and signature in a subclass.

• Overloading: same method name but different parameters (can be in the same or different classes).

---

11.6 The Object Class and toString()

• All Java classes implicitly inherit from java.lang.Object.

• toString() is defined in Object, but often overridden for better output.

• Example:

  public String toString() {
    return "created on " + dateCreated + "\ncolor: " + color + " and filled: " + filled;
  }

---

11.7 Polymorphism

• A superclass reference can refer to a subclass object.

• Subtype: defined by a subclass; supertype: defined by a superclass.

• Enables flexibility and dynamic method behavior.

---

11.8 Dynamic Binding

• The JVM determines at runtime which method implementation to invoke based on the actual type of the object.

• Declared type determines what methods can be called; actual type determines which implementation is executed.

---

11.9 Casting Objects and instanceof

• Upcasting: Subclass → Superclass: automatic.

• Downcasting: Superclass → Subclass: explicit and may require instanceof for safety.

• Syntax:

  if (obj instanceof Circle) {
    Circle c = (Circle) obj;
  }

---

11.10 The equals Method

• Default in Object compares memory addresses.

• Override to define logical equality.

---

11.11 The ArrayList Class

• A flexible array-like structure that holds objects.

• Methods: add(), remove(), get(), size(), etc.

---

11.12 Custom Stack Class Using ArrayList

• Demonstrates how to build a stack (LIFO) using ArrayList.

---

11.13 The protected Modifier

• protected members can be accessed:

  • Within the same package

  • By subclasses (even in different packages)

---

11.14 The final Modifier

• Final class: cannot be extended.

• Final method: cannot be overridden.

• Example:

  public final class Math {}
  public final void methodName() {}

---

Summary of Key Concepts

• Inheritance promotes reuse.

• Overriding and dynamic binding enable polymorphic behavior.

• Use super, protected, and final appropriately.

• Utilize type casting and instanceof for safe object manipulation.

• Understand the difference between overloading and overriding.

---

Here are detailed notes for Chapter 12: GUI Basics from "Introduction to Java Programming, 9th Edition" by Y. Daniel Liang:

---

Chapter 12: GUI Basics

12.1 Introduction

• Java GUI programming illustrates core OOP principles.

• GUI components interact through objects, containers, and layout managers.

• Swing is the primary GUI toolkit used in modern Java applications.

---

12.2 Swing vs. AWT

• AWT (Abstract Window Toolkit): platform-dependent, less flexible.

• Swing: platform-independent, lightweight, more powerful.

• Swing classes are prefixed with J (e.g., JButton vs. AWT's Button).

---

12.3 Java GUI API Overview

• Three types of GUI-related classes:

  • Component classes: JButton, JLabel, etc.

  • Container classes: JFrame, JPanel, JDialog, etc.

  • Helper classes: Color, Font, Graphics, etc.

• Class hierarchy:

  • Object → Component → Container → JComponent → Swing components.

---

12.4 Frames

• A frame is a window that holds components (e.g., buttons, labels).

• Created using JFrame.

• Must set:

  • setTitle(), setSize(), setLocationRelativeTo(null), setDefaultCloseOperation(), setVisible(true).

---

12.5 Layout Managers

• Define how components are arranged.

• FlowLayout: left-to-right, top-to-bottom (default for JPanel).

• GridLayout: rectangular grid.

• BorderLayout: divides area into five regions (NORTH, SOUTH, EAST, WEST, CENTER).

• Use setLayout() to apply a layout to a container.

---

12.6 Using Panels

• JPanel: a container that can hold a group of components.

• Useful for modular designs and nested layouts.

• Helps manage complex GUI layouts.

---

12.7 The Color Class

• Defines colors using RGB values (new Color(r, g, b) where 0 ≤ r,g,b ≤ 255).

• Predefined constants: Color.RED, Color.BLUE, etc.

• Set background/foreground with:

  • setBackground(Color), setForeground(Color).

---

12.8 The Font Class

• Fonts have name, style, and size.

• Created using: new Font("Serif", Font.BOLD, 16).

• Styles: Font.PLAIN, Font.BOLD, Font.ITALIC.

---

12.9 Common Features of Swing Components

• All Swing components inherit from JComponent.

• Shared properties:

  • Font, color, size, tooltip text (setToolTipText()), borders.

• Use setBorder() for decorating components.

---

12.10 Image Icons

• Images can be displayed using ImageIcon.

• Can be applied to JLabel, JButton, etc.

  ImageIcon icon = new ImageIcon("image/path.png");
  JLabel label = new JLabel("Text", icon, JLabel.CENTER);

---

12.11 JButton

• A button component that can contain text, icons, or both.

• Register event listeners to respond to user actions (covered in Ch. 16).

---

12.12 JCheckBox

• A GUI element with a label and a checkbox.

• Represents binary choices.

• Use isSelected() to check state.

---

12.13 JRadioButton

• Represents mutually exclusive options.

• Use ButtonGroup to group radio buttons.

  ButtonGroup group = new ButtonGroup();
  group.add(rb1);
  group.add(rb2);

---

12.14 JLabel

• Displays text, icons, or both.

• Properties:

  • horizontalAlignment, verticalAlignment, horizontalTextPosition, verticalTextPosition.

---

12.15 JTextField

• Single-line text input field.

• Methods:

  • getText(), setText(String), setEditable(false).

  • Constructor options for setting initial text and column width.

---

Chapter Summary Highlights

1. Containers use layout managers to position components.

2. JPanel helps group components.

3. Colors are defined using RGB or named constants.

4. Fonts and tool tips enhance GUI appearance.

5. Components share common properties via inheritance.

---

Chapter 13: Graphics

---

Chapter 13: Graphics

13.1 Introduction

• Graphics programming enables custom drawings in Java GUI.

• Examples: clocks, pie charts, stop signs.

• Java graphics are based on a coordinate system: origin (0,0) is top-left, x increases right, y increases downward.

---

13.2 The Graphics Class

• Every GUI component has a graphics context represented by a Graphics object.

• Common drawing methods:

  • drawString(String s, int x, int y)

  • drawLine(int x1, int y1, int x2, int y2)

  • drawRect, fillRect, drawOval, fillOval, etc.

• Override paintComponent(Graphics g) in a class that extends JPanel to draw on it.

• Always call super.paintComponent(g) at the beginning to clear the drawing area.

---

13.3 Drawing Strings, Lines, Rectangles, and Ovals

• Use methods like drawString(), drawLine(), drawRect(), fillRect(), drawOval(), and fillOval().

• Dimensions are in pixels.

• Good for rendering text and basic shapes.

---

13.4 Case Study: FigurePanel Class

• A reusable component to draw different shapes based on a property.

• Shapes include lines, rectangles, round rectangles, and ovals.

• Useful for building flexible GUI components.

---

13.5 Drawing Arcs

• Use drawArc() and fillArc().

• Arc defined by bounding rectangle, start angle, and arc angle.

• Can draw pies and circular charts.

---

13.6 Drawing Polygons and Polylines

• Use drawPolygon(), fillPolygon(), drawPolyline().

• Coordinates are passed as arrays of x and y values.

• Also supports the Polygon class.

---

13.7 Using FontMetrics to Center Text

• FontMetrics helps measure string width and height for precise positioning.

• Useful for centering or aligning text.

• Methods: getAscent(), getDescent(), getHeight(), stringWidth().

---

13.8 Case Study: MessagePanel Class

• A custom component for displaying a message.

• Can set font, alignment, rotation, and other properties.

• Demonstrates use of graphics transformation and text rendering.

---

13.9 Case Study: StillClock Class

• A reusable analog clock component.

• Uses trigonometric formulas to draw hour, minute, and second hands.

• Updates with the current time using Calendar.

---

13.10 Displaying Images

• Use ImageIcon for basic display in JLabel.

• For more control, use Graphics.drawImage() with Image objects.

• Override paintComponent() for flexible image rendering.

• Use getImage() from ImageIcon to get a drawable Image.

---

13.11 Case Study: ImageViewer Class

• Custom component for displaying images with options like stretching or positioning.

• Properties: image, stretched, x/y coordinates.

• Uses repaint() to update the image dynamically.

---

Java 2D Graphics (Bonus: Advanced Topics from Summary)

• Graphics2D class provides enhanced rendering (rotation, scaling, transformation).

• Shapes: Line2D, Rectangle2D, Arc2D, Ellipse2D, Path2D, etc.

• Stroke, Paint, GradientPaint, TexturePaint for styling.

• Supports constructive area geometry (add, subtract, intersect shapes).

---

Key Points Summary

1. Use paintComponent(Graphics g) in custom JPanel subclasses for drawing.

2. Call super.paintComponent(g) to avoid painting issues.

3. Use Graphics methods for shapes and text.

4. Use FontMetrics for measuring and aligning text.

5. Use drawImage() for displaying images in a panel.

6. For advanced graphics, use Graphics2D and Java 2D API.

---

Here are detailed notes for Chapter 15: Abstract Classes and Interfaces from "Introduction to Java Programming, 9th Edition" by Y. Daniel Liang:

---

Chapter 15: Abstract Classes and Interfaces

15.1 Introduction

• Abstract classes and interfaces define common behavior for related or unrelated classes.

• A superclass models shared features. An interface provides a flexible way to define capabilities across unrelated classes.

---

15.2 Abstract Classes

• Abstract class: A class that cannot be instantiated.

• Contains abstract methods (no implementation) and concrete methods.

• Example:

  public abstract class GeometricObject {
    public abstract double getArea();
    public abstract double getPerimeter();
  }

• Used to enforce common method structure in subclasses like Circle and Rectangle.

---

15.3 Case Study: Abstract Number Class

• Number is an abstract superclass of all numeric wrapper classes (e.g., Integer, Double).

• Defines abstract methods like intValue(), doubleValue() to standardize numeric conversions.

---

15.4 Case Study: Calendar and GregorianCalendar

• Calendar is an abstract class for date/time.

• GregorianCalendar is a concrete subclass used for calendar calculations.

---

15.5 Interfaces

• Interface: A class-like construct with only constants and abstract methods.

• Cannot be instantiated.

• Syntax:

  public interface Edible {
    String howToEat();
  }

• A class implements an interface to agree to fulfill its contract.

• Example: Chicken implements Edible and overrides howToEat().

---

15.6 The Comparable Interface

• Declares the compareTo() method for sorting objects.

• Classes like String and Integer implement it.

• Custom classes can implement it to define natural ordering.

---

15.7 The Cloneable Interface

• Marker interface: No methods—only marks a class as cloneable.

• Used with Object.clone() to allow object copying.

• If a class does not implement Cloneable, calling clone() throws CloneNotSupportedException.

---

15.8 Interfaces vs. Abstract Classes

Feature	Abstract Class	Interface
Variables	Any type	public static final only
Methods	Concrete + abstract	Only public abstract
Inheritance	Single	Multiple
Constructors	Yes	No

• Use abstract classes for "is-a" relationships (strong hierarchy).

• Use interfaces for capabilities (e.g., comparable, edible) across unrelated types.

---

15.9 Case Study: The Rational Class

• Models rational numbers (a/b).

• Implements Comparable<Rational> and extends Number.

• Methods:

  • Arithmetic operations: add(), subtract(), multiply(), divide()

  • Conversion: intValue(), doubleValue(), etc.

  • Immutability: Internal state can't change after creation.

---

Key Takeaways

1. Abstract classes define a base for shared design with partial implementation.

2. Interfaces define a contract for capabilities and support multiple inheritance.

3. Use abstract classes when behavior is shared; use interfaces when behavior is desired across types.

4. Java favors interface-based design for flexibility and scalability.

---

Here are detailed notes for Chapter 16: Event-Driven Programming from "Introduction to Java Programming, 9th Edition" by Y. Daniel Liang:

---

Chapter 16: Event-Driven Programming

16.1 Introduction

• In event-driven programming, the program responds to user actions like button clicks, key presses, or timer ticks.

• Events are fired by source objects and handled by event listeners.

---

16.2 Events and Event Sources

• An event is an object that signals something happened (e.g., ActionEvent, MouseEvent, KeyEvent).

• A source object is the GUI component that generates the event (e.g., a JButton).

• EventObject is the root class for all event types.

---

16.3 Listeners, Registrations, and Handling Events

• An event listener is an object that implements a listener interface and processes the event.

• Registering listeners: Source object uses addXListener() methods (e.g., addActionListener()).

• Handler methods:

  • actionPerformed(ActionEvent e) for ActionListener

  • mousePressed(MouseEvent e) for MouseListener

  • keyPressed(KeyEvent e) for KeyListener

---

16.4 Inner Classes

• Listener classes can be defined as inner classes.

• They have direct access to members of the outer class.

---

16.5 Anonymous Inner Classes

• Can define and register the listener in one step.

• Useful for simple, one-time-use listeners:

  button.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent e) {
          System.out.println("Button clicked");
      }
  });

---

16.6 Alternative Listener Definitions

• You can also:

  • Let the frame class implement the listener interface directly.

  • Use a single listener for multiple components and differentiate via getSource().

---

16.7 Case Study: Loan Calculator

• Demonstrates building a full GUI app that handles events from text fields and a button.

• Showcases how components work together in a real application.

---

16.8 Mouse Events

• Mouse events include clicks, presses, releases, enters, exits, moves, and drags.

• Two interfaces:

  • MouseListener: mouseClicked(), mousePressed(), etc.

  • MouseMotionListener: mouseDragged(), mouseMoved()

---

16.9 Listener Interface Adapters

• For interfaces with multiple methods, Java provides adapter classes with empty method bodies (e.g., MouseAdapter).

• Use adapters to avoid implementing all methods:

  panel.addMouseListener(new MouseAdapter() {
      public void mouseClicked(MouseEvent e) {
          // handle click
      }
  });

---

16.10 Key Events

• KeyListener processes:

  • keyPressed()

  • keyReleased()

  • keyTyped()

• To receive key events, a component must be focusable and have focus.

---

16.11 Animation Using javax.swing.Timer

• Timer fires ActionEvent at fixed intervals.

• Used for animations or periodic updates (e.g., clocks, moving objects).

• Create a timer:

  Timer timer = new Timer(1000, listener);
  timer.start();

---

Key Concepts Recap

1. Event-driven programming is driven by user and system events.

2. Components act as event sources; classes implement listener interfaces to handle events.

3. Use addXListener() to register listeners.

4. Timer-based animations are implemented using the javax.swing.Timer class.

5. Inner and anonymous classes make listener code cleaner and more modular.

---

Here are detailed notes on Chapter 17: GUI Components from "Introduction to Java Programming, 9th Edition" by Y. Daniel Liang:

---

Chapter 17: GUI Components

17.1 Introduction

• Expands GUI programming with additional Swing components.

• Builds on Chapter 16’s event-handling concepts.

• New components covered: JTextArea, JComboBox, JList, JScrollBar, JSlider.

---

17.2 Events for JCheckBox, JRadioButton, and JTextField

• GUI components can fire various event types:

  • ItemEvent: when state changes (checked/unchecked).

  • ActionEvent: triggered by pressing Enter or clicking.

• A program can use checkboxes for font styles, radio buttons for color selection, and a text field to change label content.

---

17.3 JTextArea

• For multi-line text input/output.

• Key methods:

  • append(String s): adds text.

  • setLineWrap(true): enables word wrap.

• Often embedded in a JScrollPane to add scrolling capabilities.

---

17.4 JComboBox

• Drop-down menu that lets users select one item.

• Can be editable or non-editable.

• addItem(), getSelectedItem(), and setSelectedItem() are common methods.

---

17.5 JList

• Used for selecting one or multiple items from a list.

• Configurable for single or multiple selection modes.

• Usually embedded in a JScrollPane.

---

17.6 JScrollBar

• Represents adjustable sliders with arrows.

• Can be horizontal or vertical.

• Less flexible than JSlider, usually used for scrolling control.

---

17.7 JSlider

• More versatile than JScrollBar.

• Can be configured with tick marks and labels.

• Allows smooth or snap-to-tick adjustments.

---

17.8 Creating Multiple Windows

• Use JFrame to launch multiple independent windows.

• Key tip: you cannot add a JFrame to a container, but you can create a separate frame and set it visible.

• Case Study: MultipleWindowsDemo uses a main frame with a text area and a button, and opens a second frame showing a histogram when the button is clicked.

---

Case Study Highlights

• MultipleWindowsDemo:

  • Inputs text in a main window.

  • Calculates letter frequency.

  • Displays results in a histogram within a new window.

---

Summary of Key Concepts

1. JCheckBox, JRadioButton, and JTextField events expand user input capabilities.

2. JTextArea handles multi-line text.

3. JComboBox and JList allow selection from a set of choices.

4. JScrollBar and JSlider provide user-controlled value ranges.

5. Multiple windows can be created using JFrame instances shown conditionally.

---