Question

Java Swing中setLayout（null）不能显示按钮

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

public class LoginFace extends JFrame {
public LoginFace() {
this.setLayout(null);
this.setTitle("运动会管理系统");
this.setResizable(false);
this.setVisible(true);
this.setSize(700, 500);
IDLabel.setLocation(40, 40);
this.add(IDLabel);
}

public static void main(String args[]) {
LoginFace login = new LoginFace();
}

private JLabel IDLabel=new JLabel("账号:");
private JLabel PsdLabel=new JLabel("密码:");
private JLabel RemindLabel=new JLabel();
private JTextField IDField=new JTextField();
private JPasswordField PsdField=new JPasswordField();
private JButton LoginButton=new JButton("登录");

}

Answer 1

你对setLayout方法不太了解,我从java_api给你copy出了setLayout的用法如下:
setLayout(LayoutManager mgr)
Sets the layout manager for this container.
以为着你才必须传布局对象进去,布局对象可以不写,但不可传空值啊.
其他的控件你自己加咯.
import java.awt.*;
import javax.swing.*;

public class LoginFace extends JFrame {
public LoginFace() {
//this.setLayout(null);
this.setTitle("运动会管理系统");
this.setResizable(false);
this.setVisible(true);
this.setSize(700, 500);
IDLabel.setLocation(40, 40);
this.add(IDLabel);
}

public static void main(String args[]) {
LoginFace login = new LoginFace();
}

private JLabel IDLabel=new JLabel("账号:");
private JLabel PsdLabel=new JLabel("密码:");
private JLabel RemindLabel=new JLabel();
private JTextField IDField=new JTextField();
private JPasswordField PsdField=new JPasswordField();
private JButton LoginButton=new JButton("登录");

}
或者可以:
import java.awt.*;
import javax.swing.*;

public class LoginFace extends JFrame {
public LoginFace() {
this.setLayout(new FlowLayout());
this.setTitle("运动会管理系统");
this.setResizable(false);
this.setVisible(true);
this.setSize(700, 500);
IDLabel.setLocation(40, 40);
this.add(IDLabel);
}

public static void main(String args[]) {
LoginFace login = new LoginFace();
}

private JLabel IDLabel=new JLabel("账号:");
private JLabel PsdLabel=new JLabel("密码:");
private JLabel RemindLabel=new JLabel();
private JTextField IDField=new JTextField();
private JPasswordField PsdField=new JPasswordField();
private JButton LoginButton=new JButton("登录");

}

Answer 2

在主框架中你没有添加按钮这个组件，你只添加了IDLabel这个组件了，所以看不到按钮。。。

Answer 3

this.setLayout(new FlowLayout());
别设置null，不设置还有默认展示的