Java Examples Collection

A curated collection of Java study notes and code snippets organized in Markdown. Each file explores core concepts with runnable examples, clear explanations, and practical exercises. Perfect for quick reviews, interview prep, or learning Java fundamentals.

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Table of Contents

• Examples Overview
• Quick Start
• Usage Guide
• Contributing

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Examples Overview

Example 1: Math, Arrays, and Algorithms

Fundamental algorithms and array operations:

• Integer Square Root - Find largest k where k² ≤ n
• Pi Approximation - Leibniz series implementation
• Standard Deviation - Statistical computation with arrays
• Array Reversal - Both recursive and iterative approaches
• Matrix Addition - 2D array operations

Example 2: Memory, Graphics, and Coordinate Systems

Object memory models and AWT/Swing graphics:

• Memory Layout - Object structure and byte allocation
• Graphics Methods - Paint methods for shapes and patterns
• Responsive Drawing - Dynamic grid and circle rendering
• Window Sizing - Working with current dimensions

Example 3: OOP, Inheritance, and UML

Object-oriented programming fundamentals:

• Inheritance Hierarchy - GeometricObject base class with Circle, Rectangle, Triangle
• UML Diagrams - Point and Polygon class structures
• OOP Concepts - Method overloading, overriding, and packages
• Access Modifiers - Complete reference table
• Design Patterns - University class hierarchy case study

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Quick Start

Prerequisites

• Java 8 or higher
• Any Java IDE (IntelliJ IDEA, Eclipse, VS Code with Java extensions)
• Or just javac and a text editor

Running Examples

1. Clone the repository

   git clone https://github.com/maxwell-hauser/java_examples_gh.git
   cd java_examples_gh

2. Browse examples in your editor or GitHub

3. Copy snippets into your IDE

   • Create a new Java class
   • Paste the method from any example
   • Add a main method to test it

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Usage Guide

Testing Numeric Methods

Create a test file Test.java:

public class Test {
    public static void main(String[] args) {
        // Test integer square root
        System.out.println("Integer sqrt of 42: " + integerK(42)); // Expected: 6
        
        // Test pi approximation
        System.out.println("Pi (10 terms): " + piApprox(10));
        
        // Test standard deviation
        double[] data = {2.0, 4.0, 4.0, 4.0, 5.0, 5.0, 7.0, 9.0};
        System.out.println("Std dev: " + standardDeviation(data));
    }
    
    // Paste methods from java_example_1.md here
    public static int integerK(int n) {
        int k = 0;
        while ((k + 1) * (k + 1) <= n) {
            k++;
        }
        return k;
    }
    
    // Add other methods...
}

Compile and run:

javac Test.java
java Test

Testing Graphics Methods

Create GraphicsDemo.java:

import javax.swing.*;
import java.awt.*;

public class GraphicsDemo extends JFrame {
    public GraphicsDemo() {
        setTitle("Graphics Demo");
        setSize(600, 400);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setVisible(true);
    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        int ww = getWidth();
        int wh = getHeight();
        
        // Paste paint logic from java_example_2.md here
        g.drawRect(20, 40, ww - 40, wh - 60);
        
        // Example: Draw concentric circles
        int diameter = Math.min(ww, wh) - 40;
        for (int r = diameter; r > 0; r -= 40) {
            g.drawOval((ww - r) / 2, (wh - r) / 2, r, r);
        }
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(GraphicsDemo::new);
    }
}

Compile and run:

javac GraphicsDemo.java
java GraphicsDemo

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Best Practices

For Numeric Methods

• Use double for fractional calculations
• Cast integers early to avoid integer division: 1.0 / 3 not 1 / 3
• Validate array indices and lengths before operations
• Consider edge cases: empty arrays, negative numbers, zero

For Array Operations

• Watch index boundaries carefully (0 to length - 1)
• Use System.arraycopy() for efficient copying
• Consider whether you need in-place or out-of-place operations
• Validate input array dimensions for 2D operations

For Graphics Programming

• Override paintComponent() in JPanel (preferred over paint() in JFrame)
• Call super.paintComponent(g) first to clear the background
• Get dimensions inside paint method: getWidth(), getHeight()
• Use SwingUtilities.invokeLater() for thread-safe GUI creation
• Consider using Graphics2D for advanced rendering

For OOP Design

• Always call super(...) in subclass constructors to initialize inherited state
• Use access modifiers intentionally: private for encapsulation, protected for inheritance
• Override toString() for debugging and logging
• Implement equals() and hashCode() together when needed
• Prefer composition over inheritance when appropriate

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Tips and Tricks

Topic	Tip
Pi Approximation	More terms = better accuracy, but diminishing returns after ~1000 terms
Array Reversal	Recursive approach is elegant but uses stack space; iterative is more efficient
Matrix Operations	Always validate dimensions match before operations
Swing Painting	Use repaint() to trigger redraws; never call paint() directly
Inheritance	Use instanceof to check object types before casting
Access Modifiers	Default (no modifier) = package-private, not the same as public

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Contributing

Contributions welcome! To add new examples or improve existing ones:

1. Fork the repository
2. Create a feature branch: git checkout -b feature/new-example
3. Add your example with clear comments and documentation
4. Ensure code follows Java conventions
5. Update README.md if adding new files
6. Submit a pull request

Style Guidelines

• Use descriptive variable names
• Include JavaDoc comments for methods
• Add inline comments for complex logic
• Use consistent indentation (4 spaces)
• Include example usage in comments

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Resources

• Oracle Java Documentation
• Java Language Specification
• Effective Java by Joshua Bloch
• Java Tutorials by Oracle

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License

This project is provided for educational purposes. Feel free to use, modify, and share.

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