sayhello对话框练习

package sayHello;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Main extends JFrame {
JButton bt1 =new JButton("说你好");

JLabel lb =new JLabel();
public Main() {
setLayout(new FlowLayout());
add(bt1);

add(lb);
this.setSize(300,200);
this.setLocationRelativeTo(null);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setVisible(true);

bt1.addActionListener(new BtListener());

}

class BtListener implements ActionListener{
public void actionPerformed(ActionEvent e) {
Child dlg =new Child(Main.this);
dlg.setSize(200,100);
dlg.setTitle("模态对话框");
dlg.setLocationRelativeTo(null);//定位在显示器正中间
dlg.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
dlg.setModal(true);//设置模态对话框
dlg.lb.setText("你好");//向对话框传值
dlg.setVisible(true);
}
}

public static void main(String[] args) {
new Main();
}

}

package sayHello;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Child  extends JDialog {

Main main =null;//表示探出此对话框的主窗口，由主窗口创建对话框时传递过来
JLabel lb =new JLabel();

public Child(Main main) {
this.main=main;//主窗口传来后，即可对主窗口及其组件进行操作
setLayout(new FlowLayout());
add(lb);
}

}