addMouseListener and identifier expected

Question

Me and my partner tried to make exit button for the lab, but we cannot figure it out why it has identifier expected error.

import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import java.awt.event.ActionListener;

public class EnterExitListener extends JFrame
{
    public static void main(String [] args)
{
  JFrame frame=new JFrame();
  final int FRAME_WIDTH=500;
  final int FRAME_HEIGHT=600;
  frame.setSize(FRAME_WIDTH,FRAME_HEIGHT);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setVisible(true);   

  class MouseEnterExitListener implements MouseListener
  {
      public void mouseEntered(MouseEvent event)
      {
          System.out.println("ENTER");
          frame.setBackground(Color.BLUE);
      }
      public void MouseExited(MouseEvent event)
      {
          System.out.println("EXIT");
          frame.setBackground(Color.RED);
      }  
      public void mouseReleased(MouseEvent event) {}
      public void mouseClicked(MouseEvent event) {}
      public void mousePressed(MouseEvent event) {} 

      MouseListener listener=new MouseListener();
      frame.addMouseListener(listener);   
   }
   }
}

If I try to compile this code, it will make this error

EnterExitListener.java:34: error: <identifier> expected
EnterExitListener.addMouseListener(listener);   
                                  ^
EnterExitListener.java:34: error: <identifier> expected
EnterExitListener.addMouseListener(listener);   
                                           ^

Answer 1

Line 34 frame.addMouseListener(listener); is currently part of your inner class definition. You cannot have a method call at that point.

import java.awt.Color; // added import
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import java.awt.event.ActionListener;

public class EnterExitListener extends JFrame
{
  public static void main(String [] args)
  {
    JFrame frame=new JFrame();
    final int FRAME_WIDTH=500;
    final int FRAME_HEIGHT=600;
    frame.setSize(FRAME_WIDTH,FRAME_HEIGHT);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);   

    class MouseEnterExitListener implements MouseListener
    {
        public void mouseEntered(MouseEvent event)
        {
            System.out.println("ENTER");
            frame.setBackground(Color.BLUE);
        }
        public void mouseExited(MouseEvent event) // lowercase 'm'
        {
            System.out.println("EXIT");
            frame.setBackground(Color.RED);
        }  
        public void mouseReleased(MouseEvent event) {}
        public void mouseClicked(MouseEvent event) {}
        public void mousePressed(MouseEvent event) {} 
    } // moved closing bracket

    MouseListener listener = new MouseEnterExitListener(); // instantiate class, not interface
    frame.addMouseListener(listener);   
  }
}