Question

为什么编写的java界面，组件显示不出来，然后改变下窗口大小就显示出来了

import javax.swing.*;
import java.awt.event.*;import java.awt.*;
public class D extends JFrame implements WindowListener,ActionListener{
public D()
{
JButton b1=new JButton("开始游戏");
setTitle("欢迎来到黑白棋游戏！");
Container c=getContentPane();
c.setLayout(new BorderLayout());
JPanel j1=new JPanel();
JLabel a=new JLabel("用户名");
JLabel b=new JLabel("密码");
JTextField f=new JTextField(4);
JTextField f1=new JTextField(6);

addWindowListener(this);
JButton b2=new JButton("注册");
b2.addActionListener(this);

j1.setBackground(Color.blue);
JPanel j2=new JPanel();
JPanel j3=new JPanel();j3.setBackground(Color.blue);
j2.add(a);j2.add(f);j1.add(b2);
j3.add(b);j3.add(f1);
c.add(j2,BorderLayout.CENTER);
c.add(j3,BorderLayout.NORTH);
j1.add(b1);
b1.addActionListener(this);
c.add(j1,BorderLayout.SOUTH);
setSize(600,400);
}
public void windowClosing(WindowEvent e)
{System.exit(0);
}
public void windowClosed(WindowEvent e){}
public void windowActivated(WindowEvent e){}
public void windowDeactivated(WindowEvent e){}
public void windowOpened(WindowEvent e){}
public void windowIconified(WindowEvent e){}
public void windowDeiconified(WindowEvent e){}
public void actionPerformed(ActionEvent e)
{SD d=new SD();
d.setVisible(true);
dispose();}
public void paint(Graphics g)
{}
public static void main(String[] args) {
D d1=new D();
d1.setVisible(true);

// TODO Auto-generated method stub

}

}

Answer 1

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

class Test extends JFrame {
JCheckBox checkbox;// 复选框
JComboBox combobox;// 下拉菜单

public Test() {

setSize(500, 500);
this.setLocation(300, 300);
setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

checkbox = new JCheckBox("控制地区显示", true);

Container c = this.getContentPane();
c.setLayout(null);
c.add(checkbox);
checkbox.setLocation(100, 0);
checkbox.setSize(120, 20);
checkbox.addActionListener(new monitor());
combobox = new JComboBox();
c.add(combobox);

combobox.addItem("北京");
combobox.addItem("上海");
combobox.addItem("深圳");
combobox.addItem("平顶山");
combobox.setLocation(300, 0);
combobox.setSize(100, 20);

}

class monitor implements ActionListener {

public void actionPerformed(ActionEvent e) {
combobox.setEnabled(checkbox.isSelected());
}
}

public static void main(String args[]) {
Test e = new Test();

}

}

参考下我刚写的吧，，，

这是我写的玩，

Answer 2

public void paint (Graphics g)
{}
这段删掉。

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另：变量名最好不要用单个字符表示，最好写完整名称，第一个单词首字母小写，其余每个单词首字母大写，这是 Java 命名规范。你那样写很忌的，看不清楚，错了又找不出来，自己都会忘记什么是什么。