import static javax.swing.SpringLayout.EAST;
import static javax.swing.SpringLayout.SOUTH;
import static javax.swing.SpringLayout.WIDTH;
import java.awt.Color;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.Spring;
import javax.swing.SpringLayout;
import javax.swing.SwingConstants;
import javax.swing.WindowConstants;
public class Main {
public static void main(String[] args) {
SpringLayout layout = new SpringLayout();
JPanel p = new JPanel(layout);
p.setBorder(BorderFactory.createLineBorder(Color.GREEN, 10));
JLabel l1 = new JLabel("label: width=90%", SwingConstants.CENTER);
l1.setBorder(BorderFactory.createLineBorder(Color.RED, 1));
JButton l2 = new JButton("button: width=50%");
Spring panelw = layout.getConstraint(WIDTH, p);
SpringLayout.Constraints c1 = layout.getConstraints(l1);
c1.setX(Spring.constant(0));
c1.setY(Spring.constant(20));
c1.setWidth(Spring.scale(panelw, 0.9f));
p.add(l1);
SpringLayout.Constraints c2 = layout.getConstraints(l2);
c2.setWidth(Spring.scale(panelw, 0.5f));
layout.putConstraint(SOUTH, l2, -20, SOUTH, p);
layout.putConstraint(EAST, l2, -20, EAST, p);
p.add(l2);
JFrame f = new JFrame();
f.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
f.getContentPane().add(p);
f.setSize(320, 240);
f.setVisible(true);
}
}