How can I remove just the Maximize button from a JFrame?

You can't remove the button from a JFrame. Use a JDialog instead. It doesn't have a maximize button.

In JFrame properties -> maximumSize = minimumSize. And resizable = false. Done! The button is disabled.

Make it not resizable:

frame.setResizable(false);

You will still have the minimize and close buttons.

import java.awt.event.WindowAdapter; 
import java.awt.event.WindowEvent;    
import javax.swing.JDialog; import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test extends JDialog {
    public Test(JFrame frame, String str) {
        super(frame, str);
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent evt) {
                System.exit(0);
            }
        });
    }

    public static void main(String[] args) {
        try {
            Test myFrame = new Test(new JFrame(), "Removing maximize button");
            JPanel panel = new JPanel();
            panel.setSize(100, 100);
            myFrame.add(panel);
            myFrame.setSize(100, 100);
            myFrame.setVisible(true);
        } catch (IllegalArgumentException e) {
            System.exit(0);
        }
    } }