Java应用领域探究——从桌面应用到Web开发 |21xrx.com

Java应用领域探究——从桌面应用到Web开发

2023-06-14 20:52:56 深夜i -- --

Java 应用领域桌面应用 Web开发代码案例

Java语言的强大和全面性使其成为应用开发的首选语言之一。Java应用领域广泛，从简单的桌面应用程序到大型企业级Web应用程序，都可以使用Java来开发。

1. 桌面应用程序：Java提供了Swing和AWT等GUI库，可以轻松创建桌面应用程序。以下是一个使用Swing库的简单计算器示例：


import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Calculator extends JFrame implements ActionListener {
  private JTextField display;
  private double num1, num2, result;
  private char operator;
  public Calculator() {
    super("计算器");
    setSize(200, 200);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JPanel panel = new JPanel(new BorderLayout());
    display = new JTextField("0.0", 20);
    panel.add(display, BorderLayout.NORTH);
    JPanel keypad = new JPanel(new GridLayout(4, 4));
    String[] labels = {"7", "8", "9", "/", "4", "5", "6", "*", "1", "2", "3", "-", "0", ".", "=", "+"};
    for (int i = 0; i < labels.length; i++) {
      JButton button = new JButton(labels[i]);
      button.addActionListener(this);
      keypad.add(button);
    }
    panel.add(keypad, BorderLayout.CENTER);
    setContentPane(panel);
    setVisible(true);
  }
  public void actionPerformed(ActionEvent e) {
    String label = e.getActionCommand();
    switch (label.charAt(0)) {
      case '0': case '1': case '2': case '3': case '4':
      case '5': case '6': case '7': case '8': case '9':
        if (operator == '\0') {
          num1 = Double.parseDouble(display.getText());
          display.setText(label);
        } else {
          num2 = Double.parseDouble(display.getText());
          display.setText(label);
        }
        break;
      case '+': case '-': case '*': case '/':
        operator = label.charAt(0);
        break;
      case '.':
        display.setText(display.getText() + ".");
        break;
      case '=':
        num2 = Double.parseDouble(display.getText());
        switch (operator) {
          case '+': result = num1 + num2; break;
          case '-': result = num1 - num2; break;
          case '*': result = num1 * num2; break;
          case '/': result = num1 / num2; break;
        }
        display.setText("" + result);
        operator = '\0';
        break;
    }
  }
  public static void main(String[] args) {
    new Calculator();
  }
}

2. 服务器应用程序：Java SE和Java EE提供了Socket和Servlet等类库，可以用来开发服务器应用程序。以下是一个简单的Socket服务器示例：


import java.io.*;
import java.net.*;
public class Server {
  public static void main(String[] args) {
    try {
      ServerSocket server = new ServerSocket(8000);
      while (true) {
        Socket client = server.accept();
        new Handler(client).start();
      }
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}
class Handler extends Thread {
  private Socket client;
  public Handler(Socket client)
    this.client = client;
  
  @Override
  public void run() {
    try {
      BufferedReader input = new BufferedReader(new InputStreamReader(client.getInputStream()));
      PrintWriter output = new PrintWriter(new OutputStreamWriter(client.getOutputStream()));
      String line;
      while ((line = input.readLine()) != null) {
        output.println("Echo: " + line);
        output.flush();
      }
      input.close();
      output.close();
      client.close();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

3. Web应用程序：Java EE提供了Servlet和JSP等技术，用于开发动态Web应用程序。以下是一个简单的Servlet示例：


import java.io.*;
import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.*;
@WebServlet("/HelloServlet")
public class HelloServlet extends HttpServlet {
  private static final long serialVersionUID = 1L;
  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String name = request.getParameter("name");
    response.setContentType("text/html;charset=UTF-8");
    PrintWriter out = response.getWriter();
    out.println("");
    out.println(" 
 Hello " + name + "");
    out.println("");
    out.println("
Hello " + name + ""); 
    out.println("");
    out.println("");
    out.close();
  }
}

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