InputWH.java

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.GridLayout;

import javax.swing.JComponent;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.UIManager.LookAndFeelInfo;
import javax.swing.event.AncestorEvent;
import javax.swing.event.AncestorListener;

public class InputWH {
	public int width;
	public int height;
	Draw draw = new Draw();

	InputWH() {
		showInput();
	}

	private void showInput() {
		for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
	        if ("Nimbus".equals(info.getName())) {
	            try {
					UIManager.setLookAndFeel(info.getClassName());
				} catch (ClassNotFoundException | InstantiationException
						| IllegalAccessException
						| UnsupportedLookAndFeelException e) {
					
					e.printStackTrace();
				}
	            break;
	        }
	    }
		JPanel p = new JPanel(new BorderLayout(5, 5));
		JPanel labels = new JPanel(new GridLayout(0,1,2,2));
		JPanel labels1 = new JPanel(new FlowLayout());
		labels.add(new JLabel("Width", SwingConstants.RIGHT));
		labels.add(new JLabel("Height", SwingConstants.RIGHT));
		labels1.add(new JLabel("Minimum Width:900, Height: 800"));
		p.add(labels, BorderLayout.WEST);
		p.add(labels1, BorderLayout.SOUTH);

		JPanel controls = new JPanel(new GridLayout(0, 1, 2, 2));
		JTextField widthField = new JTextField();
		controls.add(widthField);
		JTextField heightField = new JTextField();
		heightField.addAncestorListener(new RequestFocusListener(false));
		controls.add(heightField);
		p.add(controls, BorderLayout.CENTER);
		JOptionPane.showMessageDialog(null, p, "Enter Canvas Width and Height",
				JOptionPane.QUESTION_MESSAGE);
		try {
			width = Integer.parseInt(widthField.getText());
			height = Integer.parseInt(heightField.getText());
			if(width<900 || height <800){
				JOptionPane.showMessageDialog(null, p,
						"W:900,H:800 Minimum required", JOptionPane.ERROR_MESSAGE);
			}
			draw.setWH(width, height);
			draw.openPaint();
		} catch (IllegalArgumentException e) {
			JOptionPane.showMessageDialog(null, p,
					"Please enter valid number!", JOptionPane.ERROR_MESSAGE);
		}
	}

	/**
	 * @param args
	 *            none
	 */
	public static void main(String[] args) {
		SwingUtilities.invokeLater(new Runnable() {
			@Override
			public void run() {
				new InputWH();
			}
		});
	}

}

class RequestFocusListener implements AncestorListener {
	private boolean removeListener;

	public RequestFocusListener() {
		this(true);
	}


	public RequestFocusListener(boolean removeListener) {
		this.removeListener = removeListener;
	}

	@Override
	public void ancestorAdded(AncestorEvent e) {
		JComponent component = e.getComponent();
		component.requestFocusInWindow();

		if (removeListener)
			component.removeAncestorListener(this);
	}

	@Override
	public void ancestorMoved(AncestorEvent e) {
	}

	@Override
	public void ancestorRemoved(AncestorEvent e) {
	}
}