java GridBagLayout anchor

问题:

Learing GridBagLayout, The issue here is, the name label and combox don't show up on the top of the panel, but I have set its anchor to NORTH. Why ?

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();
    }
}

回答1:

You have to change

gridBagConstraints.weighty = 0.0;

to

gridBagConstraints.weighty = 1.0;

otherwise the area reserved for the component is slimmed to the size of the component, and it doesn't matter in which direction you "anchor" the component.

The result after changing the weighty is the following: