java GridBagLayout锚点

学习GridBagLayout,这里的问题是,名称标签和combox没有显示在面板的顶部,但我已将其锚点设置为NORTH.为什么？

import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.GridLayout;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

public class Test2 {    
    public Test2() {
        JFrame frame = new JFrame();
        frame.setTitle("test");
        frame.getContentPane().setLayout(new GridLayout(1,2));
        frame.setSize(800,600);

        JPanel panel1 = new JPanel();
        panel1.setLayout(new GridBagLayout());

        JLabel label = new JLabel("name");
        GridBagConstraints gridBagConstraints = new GridBagConstraints();   
        gridBagConstraints.anchor = GridBagConstraints.NORTH;
        gridBagConstraints.weightx = 0.0;
        gridBagConstraints.weighty = 0.0;
        gridBagConstraints.gridx = 0;
        gridBagConstraints.gridy = 0;
        panel1.add(label,gridBagConstraints);

        String[] petStrings = { "Bird","Cat","Dog","Rabbit","Pig" };
        JComboBox petList = new JComboBox(petStrings);
        gridBagConstraints = new GridBagConstraints();
        gridBagConstraints.anchor = GridBagConstraints.NORTH;
        gridBagConstraints.fill = GridBagConstraints.HORIZONTAL;
        gridBagConstraints.weightx = 1.0;
        gridBagConstraints.weighty = 0.0;
        gridBagConstraints.gridx = 1;
        gridBagConstraints.gridy = 0;
        panel1.add(petList,gridBagConstraints);    

        frame.getContentPane().add(panel1);
        frame.getContentPane().add(new JPanel());       

        frame.setVisible(true);
        frame.setDefaultCloSEOperation(WindowConstants.EXIT_ON_CLOSE);      
    }

    public static void main(String[] args) {
        new Test2();
    }
}

解决方法

gridBagConstraints.weighty = 0.0;

至

gridBagConstraints.weighty = 1.0;

否则为组件保留的区域会缩小到组件的大小,并且无论您在哪个方向“锚定”组件.

改变重量后的结果如下：

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