JavaAwtSwing的JFrame的pack()方法,容器适配子组件大小,笔记231220

pack()是extends自Window类的方法

使此窗口的大小适合其子组件的首选大小和布局。如果其中一个尺寸小于上一次调用setMinimumSize方法指定的最小尺寸，则会自动放大窗口的宽度和高度。

如果窗口和/或其所有者还不可显示，则在计算首选大小之前，将使它们都可显示。在计算窗口的大小后对其进行验证。

@SuppressWarnings("deprecation")
    public void pack() {
        Container parent = this.parent;
        if (parent != null && parent.peer == null) {
            parent.addNotify();
        }
        if (peer == null) {
            addNotify();
        }
        Dimension newSize = getPreferredSize();
        if (peer != null) {
            setClientSize(newSize.width, newSize.height);
        }

        if(beforeFirstShow) {
            isPacked = true;
        }

        validateUnconditionally();
    }

例1 , 外容器会变成子组件的大小

import javax.swing.*;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

public class Pack测试231219 {
	public static JFrame frame = new JFrame(Thread.currentThread().getStackTrace()[1].getClassName());
    static{
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
                System.exit(0);
            }
        });
        frame.setBounds(100,100,1024,768);
    }

   
    
    static void init() {
    	
    }
    static void step1() {
    	int sleep = 3000;
    	JLabel jlb = new JLabel("""
                
                    
                    

                """
    			+
                ""+sleep+"毫秒后"
                +
                ""+"调用frame.pack()"+""
    			+
                """
    				

""");
jlb.setOpaque(true);
jlb.setBackground(Color.DARK_GRAY);
jlb.setHorizontalAlignment(JLabel.CENTER);
jlb.setVerticalAlignment(JLabel.CENTER);
frame.add(jlb, BorderLayout.CENTER);
try {
frame.setVisible(true);
Thread.sleep(sleep);
frame.pack();
}catch(Exception ex) {
ex.printStackTrace();
}
}
static void step2() {
}
public static void main(String[] arguments)throws Exception {
init(); step1(); step2 ();
}
}

效果

例2 , 如果子组件设置了 setPreferredSize() , 外容器会变成子组件setPreferredSize()的大小

这个例子中jlb.setPreferredSize(new Dimension(600,600));
jlb.setSize()无效

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

public class Pack测试231220 {
	public static JFrame frame = new JFrame(Thread.currentThread().getStackTrace()[1].getClassName());
    static{
        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                super.windowClosing(e);
                System.exit(0);
            }
        });
        frame.setBounds(100,100,1024,768);
    }

   
    
    static void init() {
    	
    }
    static void step1() {
    	int sleep = 3000;
    	JLabel jlb = new JLabel("""
                
                    
                    

                """
    			+
                ""+sleep+"毫秒后"
                +
                ""+"调用frame.pack()"+""
    			+
                """
    				
                		
    			""");
        jlb.setOpaque(true);
        jlb.setBackground(Color.DARK_GRAY);
        jlb.setHorizontalAlignment(JLabel.CENTER);
        jlb.setVerticalAlignment(JLabel.CENTER);
        frame.add(jlb, BorderLayout.CENTER);
        try {
        	frame.setVisible(true);
        	Thread.sleep(sleep);
        	jlb.setPreferredSize(new Dimension(600,600));
        	frame.pack();
        }catch(Exception ex) {
        	ex.printStackTrace();
        }
    }
    static void step2() {
    	
    }
    
    
    public static void main(String[] arguments)throws Exception {
    	
    	init(); step1(); step2 ();
    	
        
    }
    
}