Java程序设计初学者必看的5个案例 |21xrx.com

Java程序设计初学者必看的5个案例

2023-06-15 07:13:38 深夜i -- --

Java Swing库

在学习Java程序设计的过程中，初学者经常会遇到各种各样的问题，比如说如何用Java实现一个简单的计算器、如何用Java制作一个登录界面等。本文将为初学者们提供5个实用案例，帮助他们快速入门Java程序设计。

1. 简易计算器

本案例通过Java Swing库实现了一个简单的计算器程序。该程序支持加、减、乘、除四种基本算术运算，并且支持连续计算。

代码实现：


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class Calculator extends JFrame {
  public static void main(String[] args) {
    Calculator calculator = new Calculator();
  }
  private JTextField inputField = new JTextField();//用于输入的文本框
  private double result = 0;
  private String operator = "+";
  private boolean firstInput = true;
  public Calculator() {
    super("计算器");
    setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    JPanel panel = (JPanel) getContentPane();
    panel.setLayout(new BorderLayout());
    JPanel inputPanel = new JPanel();
    inputPanel.setLayout(new BorderLayout());
    inputPanel.add(inputField, BorderLayout.CENTER);
    inputField.setHorizontalAlignment(JTextField.RIGHT);
    inputField.setFont(new Font("宋体", Font.PLAIN, 20));
    panel.add(inputPanel, BorderLayout.NORTH);
    JPanel buttonPanel = new JPanel();
    buttonPanel.setLayout(new GridLayout(4, 4));
    String[] buttonNames = {"7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+"};
    for (String name : buttonNames) {
      JButton button = new JButton(name);
      button.setFont(new Font("宋体", Font.PLAIN, 20));
      button.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent evt) {
          if (name.matches("[0-9]")) {
            inputNumber(name);
          } else if (name.equals(".")) {
            inputDot();
          } else if (name.equals("=")) {
            calculate();
          } else {
            setOperator(name);
          }
        }
      });
      buttonPanel.add(button);
    }
    panel.add(buttonPanel, BorderLayout.CENTER);
    pack();
    setVisible(true);
  }
  private void inputNumber(String number) {
    if (firstInput) {
      inputField.setText(number);
      firstInput = false;
    } else if (inputField.getText().equals("0")) {
      inputField.setText(number);
    } else {
      inputField.setText(inputField.getText() + number);
    }
  }
  private void inputDot() {
    if (firstInput) {
      inputField.setText("0.");
      firstInput = false;
    } else if (inputField.getText().indexOf(".") == -1) {
      inputField.setText(inputField.getText() + ".");
    }
  }
  private void setOperator(String operator) {
    if (this.operator.equals("+")) {
      result += Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("-")) {
      result -= Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("*")) {
      result *= Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("/")) {
      result /= Double.parseDouble(inputField.getText());
    }
    inputField.setText("");
    this.operator = operator;
  }
  private void calculate() {
    if (this.operator.equals("+")) {
      result += Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("-")) {
      result -= Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("*")) {
      result *= Double.parseDouble(inputField.getText());
    } else if (this.operator.equals("/")) {
      result /= Double.parseDouble(inputField.getText());
    }
    inputField.setText(Double.toString(result));
    this.operator = "+";
    result = 0;
    firstInput = true;
  }
}

2. 圆周率计算

本案例通过蒙特卡洛算法计算了圆周率的近似值。算法的原理为，在正方形内部随机撒点，然后统计落在圆内的点数与总点数的比值，将这个比值乘以4，就可以得到圆周率的近似值。

代码实现：


public class PiCalculation {
  public static void main(String[] args) {
    int total = 100000;//总点数
    int count = 0;//在圆内的点数
    for (int i = 0; i < total; i++) {
      double x = Math.random();
      double y = Math.random();
      if (x * x + y * y <= 1) {
        count++;
      }
    }
    double pi = count * 4.0 / total;
    System.out.println("π的近似值为：" + pi);
  }
}

3. 温度转换器

本案例通过Java Swing库实现了一个摄氏度与华氏度之间的转换器，用户可以输入摄氏度或华氏度的数值，程序会自动计算出转换后的结果。

代码实现：


import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class TemperatureConverter extends JFrame {
  public static void main(String[] args) {
    TemperatureConverter converter = new TemperatureConverter();
  }
  private JTextField inputField = new JTextField();
  private JTextField resultField = new JTextField();
  private JRadioButton celsiusButton = new JRadioButton("摄氏度");
  private JRadioButton fahrenheitButton = new JRadioButton("华氏度");
  public TemperatureConverter() {
    super("温度转换器");
    setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
    JPanel panel = (JPanel) getContentPane();
    panel.setLayout(new BorderLayout());
    JPanel inputPanel = new JPanel();
    inputPanel.setLayout(new BorderLayout());
    inputPanel.add(inputField, BorderLayout.CENTER);
    inputField.setHorizontalAlignment(JTextField.RIGHT);
    inputField.setFont(new Font("宋体", Font.PLAIN, 20));
    panel.add(inputPanel, BorderLayout.NORTH);
    JPanel buttonPanel = new JPanel();
    buttonPanel.setLayout(new GridLayout(1, 2));
    buttonPanel.add(celsiusButton);
    buttonPanel.add(fahrenheitButton);
    ButtonGroup group = new ButtonGroup();
    group.add(celsiusButton);
    group.add(fahrenheitButton);
    celsiusButton.setSelected(true);
    panel.add(buttonPanel, BorderLayout.CENTER);
    JPanel resultPanel = new JPanel();
    resultPanel.setLayout(new BorderLayout());
    resultPanel.add(resultField, BorderLayout.CENTER);
    resultField.setHorizontalAlignment(JTextField.RIGHT);
    resultField.setFont(new Font("宋体", Font.PLAIN, 20));
    resultField.setEditable(false);
    panel.add(resultPanel, BorderLayout.SOUTH);
    inputField.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
        calculate();
      }
    });
    celsiusButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
        calculate();
      }
    });
    fahrenheitButton.addActionListener(new ActionListener() {
      public void actionPerformed(ActionEvent evt) {
        calculate();
      }
    });
    pack();
    setVisible(true);
  }
  private void calculate() {
    String inputText = inputField.getText().trim();
    if (inputText.matches("\\d+(\\.\\d+)?")) {
      double value = Double.parseDouble(inputText);
      if (celsiusButton.isSelected()) {
        double result = value * 9 / 5 + 32;
        resultField.setText(String.format("%.2f 华氏度", result));
      } else {
        double result = (value - 32) * 5 / 9;
        resultField.setText(String.format("%.2f 摄氏度", result));
      }
    } else {
      resultField.setText("请输入有效的温度数值");
    }
  }
}

4. 数字转中文

本案例实现了一个将阿拉伯数字转换为中文数字的程序。比如说，输入123，程序会输出一百二十三。

代码实现：


public class NumberToChinese {
  public static void main(String[] args) {
    System.out.println(toChinese(123));
  }
  private static final String[] CHINESE_DIGITS = "六";
  private static final String[] CHINESE_UNITS = "十";
  public static String toChinese(int number) {
    if (number == 0) {//特判0
      return CHINESE_DIGITS[0];
    }
    String result = "";
    int unitIndex = 0;//当前处在数字的哪个位数（个位、十位、百位……）
    while (number > 0) {
      int digit = number % 10;//取出当前位上的数字
      if (digit != 0) {//如果当前位上的数字不是0
        result = CHINESE_DIGITS[digit] + CHINESE_UNITS[unitIndex] + result;//将当前位上的数字和当前位所代表的单位（十、百、千）添加到结果中
      } else {//如果当前位上的数字是0
        if (!result.startsWith(CHINESE_DIGITS[0])) {//特判连续的0
          result = CHINESE_DIGITS[0] + result;
        }
      }
      number /= 10;
      unitIndex++;
    }
    return result;
  }
}

5. 文件拷贝

本案例演示了如何用Java代码实现文件的拷贝。将文件A复制一份到文件B中。

代码实现：


import java.io.*;
public class FileCopy {
  public static void main(String[] args) throws Exception {
    copyFile("A.txt", "B.txt");
  }
  public static void copyFile(String sourceFilePath, String targetFilePath) throws Exception {
    FileInputStream fis = new FileInputStream(sourceFilePath);
    FileOutputStream fos = new FileOutputStream(targetFilePath);
    byte[] buffer = new byte[1024];
    int length;
    while ((length = fis.read(buffer)) > 0) {
      fos.write(buffer, 0, length);
    }
    fis.close();
    fos.close();
    System.out.println("文件拷贝成功！");
  }
}

、蒙特卡洛算法、阿拉伯数字、文件拷贝

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