How to left align JPanel in JTabbedPane?

How to left align JPanel in JTabbedPane?

Problem Description:

I want to Left align the tab labeled "Unwanted Centered Panel" here is my SSCE:

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

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

public class Issue {
    
    public Issue() {
        
    }
    public JPanel buildIssuePanel() {
        GridBagLayout layout1 = new GridBagLayout();
        GridBagConstraints gbc1 = new GridBagConstraints();
        gbc1.anchor = GridBagConstraints.LINE_START;
        JPanel unWantedCenteredPanel = new JPanel(layout1);
        
        
        unWantedCenteredPanel.add(new JLabel("SHORT"),gbc1);
        return unWantedCenteredPanel;
    }
    
    public JPanel buildWiderPanel() {
        GridBagLayout layout2 = new GridBagLayout();
        GridBagConstraints gbc2 = new GridBagConstraints();
        gbc2.anchor = GridBagConstraints.LINE_START;        
        JPanel widerPanel = new JPanel(layout2);    
        widerPanel.add(new JLabel("LOOOOOOOOOOOONNNNNNNNGGGGGGGGGG"),gbc2);
        return widerPanel;
    }
    
    public void createAndShow() {
        JFrame f = new JFrame();
        JTabbedPane tp = new JTabbedPane();
        tp.addTab("Unwanted Centered Panel", buildIssuePanel());
        tp.addTab("Wider Panel",buildWiderPanel());
        f.add(tp);
        f.validate();
        f.pack();
        f.setVisible(true);
    }
    
    public static void main(String[] args) {
        Issue issue = new Issue();
        issue.createAndShow();
    }
    
}

Unwanted Centering

Wider Panel

The issue appears to be that JTabbedPane defaults to the larger JPanel child width and centers the smaller one.

I’ve tried setting:

GridBagConstraints.anchor = GridBagConstraints.LINE_START;

But that seems to get overridden. So, how do I get the JLabel with text "SHORT" to be left aligned?

Solution – 1

As @camickr suggested, adding weightx=1 made the achor=LINE_START apply itself.

import java.awt.GridBagLayout;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

public class IssueResolved {
    
    public IssueResolved() {
        
    }
    public JPanel buildIssueResolvedPanel() {
        GridBagLayout layout1 = new GridBagLayout();
        GridBagConstraints gbc1 = new GridBagConstraints();
        gbc1.anchor = GridBagConstraints.LINE_START;
        
        //adding weightx = 1 applies the anchor = LINE_START and gives a left align
        gbc1.weightx = 1;
        
        JPanel unWantedCenteredPanelNowLeftAligned = new JPanel(layout1);       
        unWantedCenteredPanelNowLeftAligned.add(new JLabel("SHORT"),gbc1);
        return unWantedCenteredPanelNowLeftAligned;
    }
    
    public JPanel buildWiderPanel() {
        GridBagLayout layout2 = new GridBagLayout();
        GridBagConstraints gbc2 = new GridBagConstraints();
        gbc2.anchor = GridBagConstraints.LINE_START;
        
        //adding weightx = 1 applies the anchor = LINE_START and gives a left align
        gbc2.weightx = 1;       
        
        JPanel widerPanel = new JPanel(layout2);    
        widerPanel.add(new JLabel("LOOOOOOOOOOOOOOOOOOONNNNNNNNNNNNNNNNNNGGGGGGGGGGGGGG"),gbc2);
        return widerPanel;
    }
    
    public void createAndShow() {
        JFrame f = new JFrame();
        JTabbedPane tp = new JTabbedPane();
        tp.setTabLayoutPolicy(JTabbedPane.WRAP_TAB_LAYOUT);
        tp.addTab("Unwanted Centered Panel Now Left Aligned", buildIssueResolvedPanel());
        tp.addTab("Wider Panel",buildWiderPanel());
        f.add(tp);
        f.validate();
        f.pack();
        f.setVisible(true);
    }
    
    public static void main(String[] args) {
        IssueResolved issueResolved = new IssueResolved();
        issueResolved.createAndShow();
    }
    
}

Left Aligned