java - Swing 中 "Container c=getContentPane();"的用途是什么？

Question

import java.awt.*;
import javax.swing.*;
public class 
import javax.swing.*;
import java.awt.*;
import javax.swing.tree.*;
import javax.swing.event.*;
/*<applet code="JT.class" width=200 height=300>
</applet>*/

public class JT extends JApplet {
    JTree tree;
    JTextField box;
    Object nodeInfo;
    String node1;
    public void init() {
        Container c=getContentPane();
        c.setLayout(new BorderLayout());
        DefaultMutableTreeNode topNode=new DefaultMutableTreeNode("qiscet");
        DefaultMutableTreeNode cou=new DefaultMutableTreeNode("Courses");
        DefaultMutableTreeNode mca=new DefaultMutableTreeNode("MCA");
        DefaultMutableTreeNode mba=new DefaultMutableTreeNode("MBA");
        DefaultMutableTreeNode tech=new DefaultMutableTreeNode("B.tech");
        topNode.add(cou);
        cou.add(mca);   
        cou.add(mba);
        cou.add(tech);
        DefaultMutableTreeNode manage=new DefaultMutableTreeNode("Management");
        DefaultMutableTreeNode ac=new DefaultMutableTreeNode("Accounts");
        DefaultMutableTreeNode sp=new DefaultMutableTreeNode("Sports");
        DefaultMutableTreeNode lib=new DefaultMutableTreeNode("Library");
        topNode.add(manage);
        manage.add(ac); 
        manage.add(sp);
        manage.add(lib);
        tree=new JTree(topNode);
        c.add(tree,BorderLayout.NORTH);
        box=new JTextField("",80);
        c.add(box,BorderLayout.SOUTH);
    }
}

我的问题是不使用“Container c=getContentPane();”我得到正确的输出。这怎么可能？这是什么原因？

Answer 1

首先，Swing 让您对 add() 和 setLayout() 之类的东西使用 getContentPane()，让您意识到存在不同的层。过了一会儿，我猜他们承认这很痛苦，所以他们在内部调用了 getContentPane()，这样您就不必再这样做了。

This was changed in JDK 1.5 :

Lastly, after seven years, we've made jFrame.add equivalent to jFrame.getContentPane().add()

And here is a link to the rationale behind the original reason.