java笔记 ItemListener

下拉菜单 和 选择框 触发ItemListener事件

//Inner class 事件处理例一
import java.awt.*;
import java.awt.event.*;
import java.net.PortUnreachableException;
import javax.swing.*;

class WindowOperator extends JFrame
{
     
    JTextField inputNumber1, inputNumber2;  // 输入框
    JComboBox choiceFuhao;                  // 下拉菜单
    JTextArea textshow;         // 输出框
    JButton button;             // 确认按钮
    OperatorListener operator;  // 监视 下拉菜单的监视器
    ComputerListener computer;  // 监视 ActionEvent 的监视器，也就是按钮

    public WindowOperator(String s)
    {
     
        init(s);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
    }

    public void init(String s)
    {
     
        setLayout(new FlowLayout());
        setTitle(s);
        setBounds(100, 100, 390, 360);

        // 实例化组件
        inputNumber1 = new JTextField(5);
        inputNumber2 = new JTextField(5);
        choiceFuhao = new JComboBox();
        button = new JButton("计算");
        choiceFuhao.addItem("选择计算符号：");
        String [] a = {
     "+", "-", "*", "/"};
        for(int i = 0; i < a.length; i++)
            choiceFuhao.addItem(a[i]);

        textshow = new JTextArea(9, 30);
        operator = new OperatorListener();
        computer = new ComputerListener();

        // 输入文本监视器
        operator.setJComBox(choiceFuhao);  // 设置下拉菜单内容
        operator.setWorkTogether(computer); // 设置监听器

        // 按钮和输出文本监视器
        computer.setJTexFiled1(inputNumber1); // 设置数字文本内容
        computer.setJTexFiled2(inputNumber2);
        computer.setJTextArea(textshow);

        // 注册符号的监听器
        choiceFuhao.addItemListener(operator);

        // 注册计算按钮的监视器
        button.addActionListener(computer);

        // 添加组件
        add(inputNumber1);
        add(choiceFuhao);
        add(inputNumber2);
        add(button);
        add(textshow);
    }

    // 实例化OperatorListener,下拉菜单的监视器
    public class OperatorListener implements ItemListener
    {
     
        JComboBox choice;
        ComputerListener workTogether;

        public void setJComBox(JComboBox box) {
      choice = box;}  // 设置下拉菜单内容
        public void setWorkTogether(ComputerListener computer) {
     workTogether = computer;}  // 设置监听器
        public void itemStateChanged(ItemEvent e)
        {
     
            String fuhao = choice.getSelectedItem().toString();  // getSelectedItem返回的是对象
            workTogether.setFuhao(fuhao);
        }

    }

    // 实例化ComputerListener，按钮的监视器
    private  class ComputerListener implements ActionListener
    {
     
        JTextField inpterNumber1, inpterNumber2;
        JTextArea textshow;
        String fuhao ;

        public void setJTexFiled1(JTextField t) {
     inputNumber1 = t;}
        public void setJTexFiled2(JTextField t) {
     inputNumber2 = t;}
        public void setJTextArea(JTextArea t)   {
     textshow = t; }
        public void setFuhao(String s) {
     fuhao = s;}

        public void actionPerformed(ActionEvent e)
        {
     
                 //将文本中的字符串转为double
                double num1 = Double.valueOf(inputNumber1.getText());
                double num2 = Double.valueOf(inputNumber2.getText());
                double sum = 0;

                // 计算
                if     (fuhao.equals("+")) {
     sum = num1 + num2;}
                else if(fuhao.equals("-")) {
     sum = num1 - num2;}
                else if(fuhao.equals("*")) {
     sum = num1 * num2;}
                else if(fuhao.equals("/")) {
     sum = num1 / num2;}
                String res = String.format("%.3f", sum);

                // 将结果转为字符串输出
                textshow.append(num1 + " " + fuhao + " " + num2 + " = " + res + "\n");

        }
    }
}


//主类
public class test
{
     
    public static void main(String args[])
    {
     
        WindowOperator win = new WindowOperator("简单计算器");
    }
}

实现ItemListener接口，覆盖函数itemStateChanged，传入参ItemEvent