Java的25个好软件

我可以回答这个问题。Java 的 25 个好软件包括 Eclipse、IntelliJ IDEA、NetBeans、Apache Maven、Spring Framework、Hibernate、Tomcat、Jetty、Jenkins、JMeter、JConsole、JProfiler、JVisualVM、Visual Paradigm、JFreeChart、JasperReports、iText、Log4j、JUnit、Mockito、Guava、Apache Commons、Google Gson、Jackson 和 Apache POI。这些软件在 Java 开发中非常常用，可以提高开发效率和代码质量。

相关问题

java计算器程序代码在软件中运行

以下是一个示例Java计算器程序的代码，您可以将其复制并在Java开发环境中运行：

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

public class Calculator extends JFrame implements ActionListener {
    private static final long serialVersionUID = 1L;
    private JPanel panel;
    private JTextField display;
    private JButton[] buttons;
    private String[] labels = { "Backspace", "", "", "CE", "C", "7", "8", "9", "/", "sqrt", "4", "5", "6",
            "*", "%", "1", "2", "3", "-", "1/x", "0", "+/-", ".", "+", "=" };
    private double result = 0;
    private String operator = "=";
    private boolean startOfNumber = true;

    public Calculator() {
        display = new JTextField(35);
        panel = new JPanel();
        display.setText("0.0");
        panel.setLayout(new GridLayout(0, 5, 3, 3));
        buttons = new JButton[25];
        int index = 0;
        for (int rows = 0; rows < 5; rows++) {
            for (int cols = 0; cols < 5; cols++) {
                buttons[index] = new JButton(labels[index]);
                buttons[index].addActionListener(this);
                panel.add(buttons[index]);
                index++;
            }
        }
        add(display, BorderLayout.NORTH);
        add(panel, BorderLayout.CENTER);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        String command = event.getActionCommand();
        if (command.charAt(0) == 'C') {
            startOfNumber = true;
            result = 0;
            operator = "=";
            display.setText("0.0");
        } else if (command.charAt(0) >= '0' && command.charAt(0) <= '9' || command.equals(".")) {
            if (startOfNumber == true) {
                display.setText(command);
            } else {
                display.setText(display.getText() + command);
            }
            startOfNumber = false;
        } else {
            if (startOfNumber) {
                if (command.equals("-")) {
                    display.setText(command);
                    startOfNumber = false;
                } else {
                    operator = command;
                }
            } else {
                double x = Double.parseDouble(display.getText());
                calculate(x);
                operator = command;
                startOfNumber = true;
            }
        }
    }

    private void calculate(double n) {
        if (operator.equals("+")) {
            result += n;
        } else if (operator.equals("-")) {
            result -= n;
        } else if (operator.equals("*")) {
            result *= n;
        } else if (operator.equals("/")) {
            try {
                result /= n;
            } catch (ArithmeticException e) {
                display.setText("Error");
            }
        } else if (operator.equals("%")) {
            result %= n;
        } else if (operator.equals("=")) {
            result = n;
        } else if (operator.equals("sqrt")) {
            result = Math.sqrt(n);
        } else if (operator.equals("1/x")) {
            try {
                result = 1 / n;
            } catch (ArithmeticException e) {
                display.setText("Error");
            }
        } else if (operator.equals("+/-")) {
            result = -n;
        }
        display.setText("" + result);
    }

    public static void main(String[] args) {
        Calculator calculator = new Calculator();
    }
}

请注意，此代码使用Java Swing库创建了一个GUI界面，其中包含数字、操作符和其他控件。 actionPerformed方法是一个事件处理程序，用于处理用户单击按钮时发生的事件。在此方法中，我们执行所选操作并更新显示结果。您可以将此代码复制并在Java开发环境中编译和运行。

用java写一个CRUD

好的，我可以回答你的问题。

CRUD是指创建(Create)、读取(Retrieve)、更新(Update)、删除(Delete)四个基本操作，是许多软件系统中最基本的数据操作。以下是一个简单的Java代码示例，用于演示如何实现CRUD操作：

首先，创建一个实体类（entity class）：

public class Person {
    private int id;
    private String name;
    private int age;

    // 构造函数
    public Person(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    // getter和setter方法
    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

接下来，创建一个数据访问对象类（data access object class），它将负责实现CRUD操作：

import java.sql.*;

public class PersonDAO {
    private Connection conn;

    // 构造函数，用于创建数据库连接
    public PersonDAO() throws SQLException {
        conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/mydatabase", "root", "password");
    }

    // 关闭数据库连接
    public void close() throws SQLException {
        if (conn != null) {
            conn.close();
        }
    }

    // 创建一个新的Person对象
    public void create(Person person) throws SQLException {
        PreparedStatement ps = conn.prepareStatement("INSERT INTO person (id, name, age) VALUES (?, ?, ?)");
        ps.setInt(1, person.getId());
        ps.setString(2, person.getName());
        ps.setInt(3, person.getAge());
        ps.executeUpdate();
        ps.close();
    }

    // 根据ID查询一个Person对象
    public Person retrieve(int id) throws SQLException {
        PreparedStatement ps = conn.prepareStatement("SELECT * FROM person WHERE id = ?");
        ps.setInt(1, id);
        ResultSet rs = ps.executeQuery();
        Person person = null;
        if (rs.next()) {
            person = new Person(rs.getInt("id"), rs.getString("name"), rs.getInt("age"));
        }
        rs.close();
        ps.close();
        return person;
    }

    // 更新一个Person对象
    public void update(Person person) throws SQLException {
        PreparedStatement ps = conn.prepareStatement("UPDATE person SET name = ?, age = ? WHERE id = ?");
        ps.setString(1, person.getName());
        ps.setInt(2, person.getAge());
        ps.setInt(3, person.getId());
        ps.executeUpdate();
        ps.close();
    }

    // 根据ID删除一个Person对象
    public void delete(int id) throws SQLException {
        PreparedStatement ps = conn.prepareStatement("DELETE FROM person WHERE id = ?");
        ps.setInt(1, id);
        ps.executeUpdate();
        ps.close();
    }
}

现在我们可以在主程序中使用PersonDAO类来执行CRUD操作了：

public class Main {
    public static void main(String[] args) throws SQLException {
        PersonDAO dao = new PersonDAO();

        // 创建一个新的Person对象
        Person p1 = new Person(1, "Alice", 25);
        dao.create(p1);

        // 查询一个