JLabel和JTextField为什么不用申请Jpanel

JLabel和JTextField是Java Swing组件库中的组件，它们都是直接继承自JComponent，而不是继承自JPanel。因此，使用JLabel和JTextField时不需要先申请JPanel，可以直接将它们添加到任何容器中，如JFrame或JDialog等。但是，如果需要将多个组件组合在一起，可以使用JPanel作为容器来布局它们。

相关问题

编写程序，利用常用组件JButton，Jlabel,JtextField等组件实现如下所示的计算器。

好的，以下是一个简单的计算器GUI程序的代码实现：

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

public class CalculatorGUI extends JFrame implements ActionListener {

    // 定义计算器界面中的组件
    private JTextField inputField;
    private JLabel resultLabel;
    private JButton button0;
    private JButton button1;
    private JButton button2;
    private JButton button3;
    private JButton button4;
    private JButton button5;
    private JButton button6;
    private JButton button7;
    private JButton button8;
    private JButton button9;
    private JButton buttonPlus;
    private JButton buttonMinus;
    private JButton buttonMultiply;
    private JButton buttonDivide;
    private JButton buttonEqual;
    private JButton buttonClear;

    // 定义计算器操作数和运算符变量
    private double num1 = 0;
    private double num2 = 0;
    private String operator = "";

    public CalculatorGUI() {
        // 初始化计算器界面
        setTitle("Calculator");
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        inputField = new JTextField(12);
        inputField.setEditable(false);
        inputField.setHorizontalAlignment(JTextField.RIGHT);

        resultLabel = new JLabel("0");
        resultLabel.setHorizontalAlignment(JLabel.RIGHT);

        button0 = new JButton("0");
        button1 = new JButton("1");
        button2 = new JButton("2");
        button3 = new JButton("3");
        button4 = new JButton("4");
        button5 = new JButton("5");
        button6 = new JButton("6");
        button7 = new JButton("7");
        button8 = new JButton("8");
        button9 = new JButton("9");

        buttonPlus = new JButton("+");
        buttonMinus = new JButton("-");
        buttonMultiply = new JButton("*");
        buttonDivide = new JButton("/");
        buttonEqual = new JButton("=");
        buttonClear = new JButton("C");

        // 设置计算器界面布局
        JPanel inputPanel = new JPanel();
        inputPanel.setLayout(new GridLayout(2, 1));
        inputPanel.add(inputField);
        inputPanel.add(resultLabel);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout(new GridLayout(4, 4));
        buttonPanel.add(button1);
        buttonPanel.add(button2);
        buttonPanel.add(button3);
        buttonPanel.add(buttonPlus);
        buttonPanel.add(button4);
        buttonPanel.add(button5);
        buttonPanel.add(button6);
        buttonPanel.add(buttonMinus);
        buttonPanel.add(button7);
        buttonPanel.add(button8);
        buttonPanel.add(button9);
        buttonPanel.add(buttonMultiply);
        buttonPanel.add(buttonClear);
        buttonPanel.add(button0);
        buttonPanel.add(buttonEqual);
        buttonPanel.add(buttonDivide);

        Container contentPane = getContentPane();
        contentPane.add(inputPanel, BorderLayout.NORTH);
        contentPane.add(buttonPanel, BorderLayout.CENTER);

        // 绑定事件监听器
        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);
        buttonPlus.addActionListener(this);
        buttonMinus.addActionListener(this);
        buttonMultiply.addActionListener(this);
        buttonDivide.addActionListener(this);
        buttonEqual.addActionListener(this);
        buttonClear.addActionListener(this);

        pack();
    }

    public void actionPerformed(ActionEvent e) {
        // 处理按钮点击事件
        String action = e.getActionCommand();

        if (action.equals("C")) {
            inputField.setText("");
            resultLabel.setText("0");
            num1 = 0;
            num2 = 0;
            operator = "";
        } else if (action.equals("+")) {
            num1 = Double.parseDouble(inputField.getText());
            inputField.setText("");
            operator = "+";
        } else if (action.equals("-")) {
            num1 = Double.parseDouble(inputField.getText());
            inputField.setText("");
            operator = "-";
        } else if (action.equals("*")) {
            num1 = Double.parseDouble(inputField.getText());
            inputField.setText("");
            operator = "*";
        } else if (action.equals("/")) {
            num1 = Double.parseDouble(inputField.getText());
            inputField.setText("");
            operator = "/";
        } else if (action.equals("=")) {
            num2 = Double.parseDouble(inputField.getText());
            double result = 0;
            switch (operator) {
                case "+":
                    result = num1 + num2;
                    break;
                case "-":
                    result = num1 - num2;
                    break;
                case "*":
                    result = num1 * num2;
                    break;
                case "/":
                    result = num1 / num2;
                    break;
            }
            resultLabel.setText(String.valueOf(result));
            inputField.setText("");
            num1 = 0;
            num2 = 0;
            operator = "";
        } else {
            inputField.setText(inputField.getText() + action);
        }
    }

    public static void main(String[] args) {
        CalculatorGUI calculator = new CalculatorGUI();
        calculator.setVisible(true);
    }
}

运行以上代码后，便可以看到一个简单的计算器界面。

import javax.swing.*; import javax.swing.border.EmptyBorder; import java.awt.*; import java.text.DecimalFormat; import java.util.regex.*; public class WeightIndex extends JFrame { private static final long serialVersionUID = 1L; private JPanel contentPane; private JLabel titleLabel; private JPanel contentPanel; private JButton submitButton; private ButtonGroup bg; private JPanel sexPanel; private JRadioButton ChinaRadio; private JRadioButton AsiaRadio; private JRadioButton WHORadio; private JPanel whPanel; private JLabel heightLabel; private JLabel weightLabel; private JTextField heightText; private JTextField weightText; private JPanel consolePanel; private JLabel consoleLabel; private JTextField consoleText; 分析一下这段代码

这段代码定义了一个名为`WeightIndex`的类，继承自`JFrame`，表示一个窗口应用程序。其中，`serialVersionUID`是一个用于序列化的静态变量。

类中包含了一系列组件，如`contentPane`、`titleLabel`、`contentPanel`、`submitButton`、`bg`、`sexPanel`、`ChinaRadio`、`AsiaRadio`、`WHORadio`、`whPanel`、`heightLabel`、`weightLabel`、`heightText`、`weightText`、`consolePanel`、`consoleLabel`、`consoleText`，它们用于创建布局和显示UI界面。

在类中使用了Java的AWT和Swing库，其中包括了`JFrame`、`JPanel`、`JLabel`、`JButton`、`ButtonGroup`、`JRadioButton`、`JTextField`等组件，用于构建UI界面。

对于代码中的`JRadioButton`，通过将它们添加到同一个`ButtonGroup`中，可以实现单选按钮的互斥。

整个类的作用是实现一个体重指数计算器的UI界面，用户可以在界面上输入身高和体重数据，选择计算方法，然后通过点击提交按钮计算体重指数并显示结果。