Question

Swing组件为什么无法显示出来？

import javax.swing.*;

public class BookFrame extends JFrame {

public JButton Add, Modify;
public JComboBox Delete, Find, Sort;

public BookFrame() {

super(" ");
Find = new JComboBox();
Find.setModel(new DefaultComboBoxModel(new String[] { "按作者查找", "按价格查找",
"按分类查找", "按出版社查找", "按书籍名查找" }));

Sort = new JComboBox();
Sort.setModel(new DefaultComboBoxModel(new String[] { "按价格排序", "按作者排序",
"按分类排序", "按购进日期排序", "按书籍名排序", "按出版社" }));

Delete = new JComboBox();
Delete.setModel(new DefaultComboBoxModel(new String[] { "按价格排序",
"按作者排序", "按分类排序", "按购进日期排序", "按书籍名排序", "按出版社" }));

Add = new JButton("添加");
Modify = new JButton("修改");

JPanel jp = new JPanel();

//jp.setLayout(new FlowLayout());
jp.setLayout(null);

jp.add(Modify);
jp.add(Find);
jp.add(Sort);
jp.add(Add);
JLabel test = new JLabel("aaaaaaaaaaaaaaaaaaaaa");
jp.add(test);

//Add.setBounds(50, 20, 10, 0);
//Modify.setBounds(50, 20, 50, 0);
//Sort.setBounds(50, 20, 90, 0);
//Delete.setBounds(50, 20, 140, 0);
//jp.setVisible(true);
this.add(jp);

this.setSize(500,500);
//jp.setVisible(true);
// jp.validate();
this.setVisible(true);
this.validate();

//BookName.setBounds(50, 10, 75, 25);
}

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

}

Answer 1

frame.setVisible(true);
frame.setSize(400,200);
这两句放在main方法的最后面。就是放在 frame.setLayout(null);这句后面。
原因：你的组件都没有初始化完成，你就已经将frame显示出来，那肯定不会有组件显示出来，除非你动一下窗口，或者点下最大化，他才会刷新出来~~
呵呵，你试试吧，我这边测试通过
请参考

Answer 2

没有设置布局方式，将this.add(jp);
改为：this.setLayout(new BorderLayout());
this.add(jp,BorderLayout.CENTER);