Java jLabel on top of another listener

Question

I want to read if one jLabel is on top of another. I drag jLabel1 on top of jLabel2 and drop it there and do something if it is on top. Code:

package javaapplication5;

import java.awt.Component;
import java.awt.Point;

public class NewJFrame extends javax.swing.JFrame {
    boolean OptionsDrag = false, OptionsDrop = false;
    private Point initialLoc;
    private Point initialLocOnScreen;
    /**
     * Creates new form NewJFrame
     */
    public NewJFrame() {
        initComponents();
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        jLabel1 = new javax.swing.JLabel();
        jLabel2 = new javax.swing.JLabel();
        jLabel3 = new javax.swing.JLabel();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setMaximumSize(new java.awt.Dimension(400, 300));
        setMinimumSize(new java.awt.Dimension(400, 300));
        getContentPane().setLayout(null);

        jLabel1.setBackground(new java.awt.Color(0, 0, 255));
        jLabel1.setOpaque(true);
        jLabel1.addMouseListener(new java.awt.event.MouseAdapter() {
        public void mousePressed(java.awt.event.MouseEvent evt) {
            jLabel1MousePressed(evt);
        }
        public void mouseReleased(java.awt.event.MouseEvent evt) {
            jLabel1MouseReleased(evt);
        }
    });
    jLabel1.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
        public void mouseDragged(java.awt.event.MouseEvent evt) {
            jLabel1MouseDragged(evt);
        }
    });
    getContentPane().add(jLabel1);
    jLabel1.setBounds(90, 130, 48, 48);

    jLabel2.setBackground(new java.awt.Color(0, 255, 255));
    jLabel2.setOpaque(true);
    jLabel2.addMouseListener(new java.awt.event.MouseAdapter() {
        public void mouseEntered(java.awt.event.MouseEvent evt) {
            jLabel2MouseEntered(evt);
        }
    });
    getContentPane().add(jLabel2);
    jLabel2.setBounds(230, 80, 48, 48);

    jLabel3.setText("showed");
    jLabel3.setVisible(false);
    getContentPane().add(jLabel3);
    jLabel3.setBounds(40, 30, 37, 20);

    pack();
}// </editor-fold>                        

private void jLabel1MousePressed(java.awt.event.MouseEvent evt) {                                     
    Component comp = (Component)evt.getSource();
    initialLoc = comp.getLocation();
    initialLocOnScreen = evt.getLocationOnScreen();
}                                    

private void jLabel1MouseReleased(java.awt.event.MouseEvent evt) {                                      
    Component comp = (Component)evt.getSource();
    Point locOnScreen = evt.getLocationOnScreen();

    int x = locOnScreen.x - initialLocOnScreen.x + initialLoc.x;
    int y = locOnScreen.y - initialLocOnScreen.y + initialLoc.y;
    comp.setLocation(x, y);
    OptionsDrop = true;
}                                     

private void jLabel1MouseDragged(java.awt.event.MouseEvent evt) {                                     
    Component comp = (Component)evt.getSource();
    Point locOnScreen = evt.getLocationOnScreen();

    int x = locOnScreen.x - initialLocOnScreen.x + initialLoc.x;
    int y = locOnScreen.y - initialLocOnScreen.y + initialLoc.y;
    comp.setLocation(x, y);
    OptionsDrag = true;
}                                    

private void jLabel2MouseEntered(java.awt.event.MouseEvent evt) {                                     
    if(OptionsDrag == true && OptionsDrop == true){
        jLabel3.setVisible(true);
    }
}                                    

/**
 * @param args the command line arguments
 */
public static void main(String args[]) {

    try {
        for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
                javax.swing.UIManager.setLookAndFeel(info.getClassName());
                break;
            }
        }
    } catch (ClassNotFoundException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (InstantiationException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (IllegalAccessException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    } catch (javax.swing.UnsupportedLookAndFeelException ex) {
        java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
    }
    //</editor-fold>

    /* Create and display the form */
    java.awt.EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            new NewJFrame().setVisible(true);
        }
    });
}
    // Variables declaration - do not modify                     
    private javax.swing.JLabel jLabel1;
    private javax.swing.JLabel jLabel2;
    private javax.swing.JLabel jLabel3;
    // End of variables declaration                   
}

I can move jLabel1 but when it's dropped on other label named Preview_1 it does nothing. I saw that when i drag and drop it's fine but it works only when i enter with the mouse on cyan block. Is it possible to do it when blue box goes on top of cyan instead mouse?

Answer 1

• I would first off rename variables so that they make the code self commenting. Yes this is a simple example program, but this little change can make all the difference.

For instance:

private javax.swing.JLabel mobileLabel;
private javax.swing.JLabel fixedLabel;
private javax.swing.JLabel notificationLabel;

• I would not add a MouseListener to the fixedLabel since you don't really care if the mouse is over it, but rather if the dragged component is.
• Rather the intersection test should be in the mobileLabel's MouseListener.
• One way to test for intersection is to extract the Rectangles of the two components (or use a for loop if you must loop through several components, extracting Rectangles as you go), and then testing if one Rectangle intersects another.
• I'm not sure if you want to center the mobileLabel on the fixedLabel if there is overlap. If so, you can get the position of the fixed one and use that to set the position of the mobile one.
• Another possible solution is to use Java's drag and drop functionality.

For example:

import java.awt.Color;
import java.awt.Component;
import java.awt.Point;
import java.awt.Rectangle;

@SuppressWarnings("serial")
public class NewJFrame2 extends javax.swing.JFrame {
   private static final String OVERLAID = "Overlaid!";
   boolean OptionsDrag = false, OptionsDrop = false;
   private Point initialLoc;
   private Point initialLocOnScreen;

   public NewJFrame2() {
      initComponents();
   }

   private void initComponents() {
      mobileLabel = new javax.swing.JLabel("Mobile");
      mobileLabel.setForeground(Color.white);
      fixedLabel = new javax.swing.JLabel("Fixed");
      notificationLabel = new javax.swing.JLabel();

      setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
      setMaximumSize(new java.awt.Dimension(400, 300));
      setMinimumSize(new java.awt.Dimension(400, 300));
      getContentPane().setLayout(null);

      mobileLabel.setBackground(new java.awt.Color(0, 0, 255));
      mobileLabel.setOpaque(true);
      mobileLabel.addMouseListener(new java.awt.event.MouseAdapter() {
         public void mousePressed(java.awt.event.MouseEvent evt) {
            jLabel1MousePressed(evt);
         }

         public void mouseReleased(java.awt.event.MouseEvent evt) {
            jLabel1MouseReleased(evt);
         }
      });
      mobileLabel.addMouseMotionListener(new java.awt.event.MouseMotionAdapter() {
         public void mouseDragged(java.awt.event.MouseEvent evt) {
            jLabel1MouseDragged(evt);
         }
      });
      getContentPane().add(mobileLabel);
      mobileLabel.setBounds(90, 130, 48, 48);

      fixedLabel.setBackground(new java.awt.Color(0, 255, 255));
      fixedLabel.setOpaque(true);
// !!     fixedLabel.addMouseListener(new java.awt.event.MouseAdapter() {
//         public void mouseEntered(java.awt.event.MouseEvent evt) {
//            jLabel2MouseEntered(evt);
//         }
//      });
      getContentPane().add(fixedLabel);
      fixedLabel.setBounds(230, 80, 48, 48);

      //!! notificationLabel.setText("showed");
      // !! notificationLabel.setVisible(false);
      getContentPane().add(notificationLabel);
      // notificationLabel.setBounds(40, 30, 37, 20); //!!
      notificationLabel.setLocation(40, 30);  //!! 
      notificationLabel.setSize(notificationLabel.getPreferredSize()); //!! 

      pack();
   }

   private void jLabel1MousePressed(java.awt.event.MouseEvent evt) {
      Component comp = (Component) evt.getSource();
      initialLoc = comp.getLocation();
      initialLocOnScreen = evt.getLocationOnScreen();
   }

   private void jLabel1MouseReleased(java.awt.event.MouseEvent evt) {
      Component comp = (Component) evt.getSource();
      Point locOnScreen = evt.getLocationOnScreen();

      int x = locOnScreen.x - initialLocOnScreen.x + initialLoc.x;
      int y = locOnScreen.y - initialLocOnScreen.y + initialLoc.y;
      comp.setLocation(x, y);
      OptionsDrop = true;

      if (compIntersectsFixed(comp)) {

         // if you want to place the mobileLabel directly on top
         // of the fixedLabel
         comp.setLocation(fixedLabel.getLocation());
         repaint();
         notificationLabel.setText(OVERLAID);
         notificationLabel.setSize(notificationLabel.getPreferredSize());
      } else {
         notificationLabel.setText("");
      }
      revalidate();
      repaint();
   }

   private boolean compIntersectsFixed(Component comp) {
      Rectangle compRect = comp.getBounds();
      Rectangle fixedRect = fixedLabel.getBounds();
      if (compRect.intersects(fixedRect)) {
         return true;
      }
      return false;
   }

   private void jLabel1MouseDragged(java.awt.event.MouseEvent evt) {
      Component comp = (Component) evt.getSource();
      Point locOnScreen = evt.getLocationOnScreen();

      int x = locOnScreen.x - initialLocOnScreen.x + initialLoc.x;
      int y = locOnScreen.y - initialLocOnScreen.y + initialLoc.y;
      comp.setLocation(x, y);
      OptionsDrag = true;
   }

// !!  private void jLabel2MouseEntered(java.awt.event.MouseEvent evt) {
//      if (OptionsDrag == true && OptionsDrop == true) {
//         notificationLabel.setVisible(true);
//      }
//   }

   public static void main(String args[]) {

      try {
         for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager
               .getInstalledLookAndFeels()) {
            if ("Nimbus".equals(info.getName())) {
               javax.swing.UIManager.setLookAndFeel(info.getClassName());
               break;
            }
         }
      } catch (ClassNotFoundException ex) {
         java.util.logging.Logger.getLogger(NewJFrame2.class.getName()).log(
               java.util.logging.Level.SEVERE, null, ex);
      } catch (InstantiationException ex) {
         java.util.logging.Logger.getLogger(NewJFrame2.class.getName()).log(
               java.util.logging.Level.SEVERE, null, ex);
      } catch (IllegalAccessException ex) {
         java.util.logging.Logger.getLogger(NewJFrame2.class.getName()).log(
               java.util.logging.Level.SEVERE, null, ex);
      } catch (javax.swing.UnsupportedLookAndFeelException ex) {
         java.util.logging.Logger.getLogger(NewJFrame2.class.getName()).log(
               java.util.logging.Level.SEVERE, null, ex);
      }

      java.awt.EventQueue.invokeLater(new Runnable() {
         @Override
         public void run() {
            new NewJFrame2().setVisible(true);
         }
      });
   }

   // !! name changes
   private javax.swing.JLabel mobileLabel;
   private javax.swing.JLabel fixedLabel;
   private javax.swing.JLabel notificationLabel;
}