Java是一种面向对象的编程语言，与许多其他编程语言不同，它既是简单的，也是强大的。如果你想玩一些有趣的代码，下面就有一些简单的Java代码示例。

1. 机器人

这个机器人程序是一个简单的示例，但它可以为你提供很多乐趣。它使用AWT和Swing库创建一个窗体，然后在窗体中绘制一个机器人。你可以使用鼠标移动机器人的头和手臂，也可以使机器人向前移动。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Robot extends JPanel implements MouseListener, MouseMotionListener {
  int x, y; // robot 的头的坐标
  int armX, armY; // 机器手臂的坐标
  boolean armGrabbed = false; // 手臂是否在运动
  int headSize = 100; // 头的半径
  int armLength = 75; // 手臂的长度
  int bodyLength = 150; // 身体长度
  int bodyWidth = 60;
  public Robot() {
   addMouseListener(this);
   addMouseMotionListener(this);
  }
  public void paint(Graphics g) {
   super.paint(g);
   Graphics2D g2d = (Graphics2D) g;
   int robotCentreX = x;
   int robotCentreY = y - headSize;
   // 旋转机器人
   g2d.rotate(Math.toRadians(armX), robotCentreX, robotCentreY);
   g2d.setColor(Color.blue);
   g2d.fillOval(x-headSize/2, y-headSize/2, headSize, headSize); // 画个圆
   g2d.setColor(Color.white);
   g2d.fillRect(x - bodyWidth/2, y, bodyWidth, bodyLength);
   g2d.setColor(Color.red);
   int armCentreX = x + bodyWidth/2;
   int armCentreY = y + bodyLength - armLength/2;
   g2d.drawLine(x, y, armCentreX, armCentreY); 
   g2d.drawLine(x+bodyWidth, y, armCentreX + armLength, armCentreY);
   g2d.setColor(Color.blue);
   if (armGrabbed) { // 机器人抓住某物
     g2d.drawLine(armCentreX, armCentreY, armX, armY);
   } else { // 机器人手臂自动运动
     g2d.drawLine(armCentreX, armCentreY, 
      armCentreX + (int) (armLength * Math.cos(Math.toRadians(armX))),
      armCentreY + (int) (armLength * Math.sin(Math.toRadians(armX))));
   }
  }
  // MouseListener 实现方法，此处略去
  public void mouseClicked(MouseEvent e) { }
  public void mouseEntered(MouseEvent e) { }
  public void mouseExited(MouseEvent e) { }
  public void mousePressed(MouseEvent e) {
   if (e.getButton() == MouseEvent.BUTTON1) // 点击鼠标左键
     armGrabbed = true;
   
  }
  public void mouseReleased(MouseEvent e) {
   if (e.getButton() == MouseEvent.BUTTON1) // 松开鼠标左键
     armGrabbed = false;
   
  }
  // MouseMotionListener 实现方法，此处略去
  public void mouseDragged(MouseEvent e) {
   if (armGrabbed) {
     armX = e.getX();
     armY = e.getY();
   }
  }
  public void mouseMoved(MouseEvent e) { }
  public static void main(String[] args) {
   JFrame frame = new JFrame("My Robot");
   frame.setContentPane(new Robot());
   frame.setSize(350, 250);
   frame.setVisible(true);
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  }
}

2. 简单计算器

这个简单计算器程序有一个文本框，用于用户输入算术表达式，以及一些按钮，用于输入操作符和数字。程序通过解析表达式和执行相应运算来显示结果。

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Calculator implements ActionListener {
  private JFrame frame;
  private JTextField textField;
  private double memory = Double.NaN;
  private char lastOperator;
  public Calculator() {
   frame = new JFrame("Calculator");
   textField = new JTextField();
   JButton button0 = new JButton("0");
   JButton button1 = new JButton("1");
   JButton button2 = new JButton("2");
   JButton button3 = new JButton("3");
   JButton button4 = new JButton("4");
   JButton button5 = new JButton("5");
   JButton button6 = new JButton("6");
   JButton button7 = new JButton("7");
   JButton button8 = new JButton("8");
   JButton button9 = new JButton("9");
   JButton buttonAdd = new JButton("+");
   JButton buttonSubtract = new JButton("-");
   JButton buttonMultiply = new JButton("*");
   JButton buttonDivide = new JButton("/");
   JButton buttonEquals = new JButton("=");
   JButton buttonClear = new JButton("C");
   button0.addActionListener(this);
   button1.addActionListener(this);
   button2.addActionListener(this);
   button3.addActionListener(this);
   button4.addActionListener(this);
   button5.addActionListener(this);
   button6.addActionListener(this);
   button7.addActionListener(this);
   button8.addActionListener(this);
   button9.addActionListener(this);
   buttonAdd.addActionListener(this);
   buttonSubtract.addActionListener(this);
   buttonMultiply.addActionListener(this);
   buttonDivide.addActionListener(this);
   buttonEquals.addActionListener(this);
   buttonClear.addActionListener(this);
   JPanel buttonPanel = new JPanel();
   buttonPanel.setLayout(new GridLayout(4,4));
   buttonPanel.add(button1);
   buttonPanel.add(button2);
   buttonPanel.add(button3);
   buttonPanel.add(buttonAdd);
   buttonPanel.add(button4);
   buttonPanel.add(button5);
   buttonPanel.add(button6);
   buttonPanel.add(buttonSubtract);
   buttonPanel.add(button7);
   buttonPanel.add(button8);
   buttonPanel.add(button9);
   buttonPanel.add(buttonMultiply);
   buttonPanel.add(buttonClear);
   buttonPanel.add(button0);
   buttonPanel.add(buttonEquals);
   buttonPanel.add(buttonDivide);
   frame.add(textField, BorderLayout.NORTH);
   frame.add(buttonPanel, BorderLayout.CENTER);
   frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   frame.setSize(200, 250);
   frame.setVisible(true); 
  }
  public void actionPerformed(ActionEvent event) {
   String text = textField.getText();
   String button_text = event.getActionCommand();
   if (button_text.equals("C")) { // 清空文本框
     memory = Double.NaN;
     textField.setText("");
   }
   else if (button_text.equals("+") || button_text.equals("-") ||
        button_text.equals("*") || button_text.equals("/")) { // 执行运算
     char operator = button_text.charAt(0);
     if (!Double.isNaN(memory)) {
      double num = Double.parseDouble(text);
      switch (lastOperator) {
        case '+': memory += num; break;
        case '-': memory -= num; break;
        case '*': memory *= num; break;
        case '/': memory /= num; break;
      }
      textField.setText("" + memory);
     } else {
      memory = Double.parseDouble(text);
     }
     lastOperator = operator;
   }
   else if (button_text.equals("=")) { // 显示运算结果
     double num = Double.parseDouble(text);
     switch (lastOperator) {
      case '+': memory += num; break;
      case '-': memory -= num; break;
      case '*': memory *= num; break;
      case '/': memory /= num; break;
     }
     textField.setText("" + memory);
     lastOperator = '=';
     memory = Double.NaN;
   }
   else { // 添加数字到文本框
     textField.setText(text + button_text);
   }
  }
  public static void main(String[] args) {
   Calculator calc = new Calculator();
  }
}

3. 数组操作

这个程序通过创建一个整数数组并调用一些Java数组函数来演示一些数组操作。它将显示数组中每个元素的值，并使用Arrays类的sort函数将它们排序。

import java.util.*;
public class ArrayOperations {
  public static void main(String[] args) {
   int[] numbers = new int[10];
   
   for (int i = 0; i < numbers.length; i++) {
     numbers[i] = (int) (Math.random() * 100);
   }
   System.out.print("Original Array: ");
   for (int i = 0; i < numbers.length; i++) {
     System.out.print(numbers[i] + " ");
   }
   Arrays.sort(numbers); // 排序
   System.out.print("\nSorted Array : ");
   for (int i = 0; i < numbers.length; i++) {
     System.out.print(numbers[i] + " ");
   }
  }
}

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