第十五节：事件实验

import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.*;


public class CaculateDemo extends JFrame implements ItemListener{
//在类中添加窗口组件作为类的成员变量
//JLabel文本
    JLabel j11,j12,j13;
//JTextField为输入框
    JTextField jtf1,jtf2,jtf3;
//JPanel为容器
    JPanel jp1,jp2,jp3,jp4;
//JRadioButton为单选按钮
    JRadioButton j1,j2,j3,j4;
//ButtonGroup 为单选组按钮
    ButtonGroup gd;

    CaculateDemo(){
//在构造方法为每个组件及容器申请内存空间
        super("计算器");
        j11=new JLabel("操作数1");
        j12=new JLabel("操作数2");
        j13=new JLabel("计算结果是：");
            
        jtf1=new JTextField(10);
        jtf2=new JTextField(10);
        jtf3=new JTextField(10);    
        
        jp1=new JPanel();
        jp2=new JPanel();
        jp3=new JPanel();
        jp4=new JPanel();
        
        j1=new JRadioButton("+");
        j2=new JRadioButton("-");
        j3=new JRadioButton("*");
        j4=new JRadioButton("/");
        
        gd=new ButtonGroup();
        
    }
    public void init(){
        this.setSize(300,300);
        this.setLocation(100,100);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
        this.setLayout(new GridLayout(4,1));
        
        jp1.setLayout(new FlowLayout(FlowLayout.LEFT));
        jp2.setLayout(new FlowLayout(FlowLayout.LEFT));
        jp3.setLayout(new FlowLayout(FlowLayout.LEFT));
        jp4.setLayout(new FlowLayout(FlowLayout.LEFT));
        
        //在容器1中加文本，输入框
        jp1.add(j11);
        jp1.add(jtf1);
        //在容器2中加文本，输入框
        jp2.add(j12);
        jp2.add(jtf2);
        
        jp3.add(j1);
        jp3.add(j2);
        jp3.add(j3);
        jp3.add(j4);
        
        gd.add(j1);
        gd.add(j2);
        gd.add(j3);
        gd.add(j4);
        
        //在容器4中加文本，输入框
        jp4.add(j13);
        jp4.add(jtf3);
        
        
        this.add(jp1);
        this.add(jp2);
        this.add(jp3);
        this.add(jp4);
        
        //添加给事件源添加监听
        j1.addItemListener(this);
        j2.addItemListener(this);
        j3.addItemListener(this);
        j4.addItemListener(this);
    }
    
    public static void main(String[] args) {
        new CaculateDemo().init();
    
    }
    //实现itemStateChanged方法
    @Override
    public void itemStateChanged(ItemEvent e) {
        
        
            try{
            double num1=Double.parseDouble(jtf1.getText());
            double num2=Double.parseDouble(jtf2.getText());
            double res=0;
            
            if(e.getSource()==j1){
                res=num1+num2;
            }else if(e.getSource()==j2){
                res=num1-num2;
            }else if(e.getSource()==j3){
                res=num1*num2;
            }else if(e.getSource()==j4){
                res=num1/num2;
            }
            jtf3.setText(res+"");
            }
            //捕获输入错误时的异常NumberFormatException，并给出错误提示到输入框中
        catch(NumberFormatException eee){
            jtf3.setText("请输入数字");
        }
    }
}