package awtDemo;
import java.awt.Dimension;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
public class setBoundsDemo {
  public static void main(String[] args) {
    // TODO Auto-generated method stub
    //设置panel的layout以及sieze
    JPanel jpanel = new JPanel();
    System.out.println("default PreferredSize is " + jpanel.getPreferredSize());
    System.out.println("default Size is " + jpanel.getSize());
    jpanel.setLayout(null);
    System.out.println("In null layout, the PreferredSize is " + jpanel.getPreferredSize());
    System.out.println("In null layout, the Size is " + jpanel.getSize());
    jpanel.setPreferredSize(new Dimension(400, 400));
    //添加按钮
    JButton button11 = new JButton("setBounds");
    JButton button12 = new JButton("setLocationAndSetSize");
    button11.setBounds(20, 20, 100, 100);
    button12.setLocation(250, 250);
    button12.setSize(100, 100);
    jpanel.add(button11);
    jpanel.add(button12);
    // 设置窗体属性
    JFrame frame = new JFrame("setBoundsDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.add(jpanel);
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

default PreferredSize is java.awt.Dimension[width=10,height=10]
default Size is java.awt.Dimension[width=0,height=0]
In null layout, the PreferredSize is java.awt.Dimension[width=0,height=0]
In null layout, the Size is java.awt.Dimension[width=0,height=0]