Why do i need to declate methods two times for this program work

Question

Hi,
why should i have to declare 2 times the methods
public void mouseClicked(MouseEvent e) {    }
public void mousePressed(MouseEvent e) {    }
public void mouseReleased(MouseEvent e) {    }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) {  }
to make this program work? why when i declate 1 time this program doesn't work good?
import java.awt.*;*
import javax.swing.;
import java.awt.datatransfer.*;
import java.io.FileReader;
import java.io.IOException;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
public class Main extends JPanel implements MouseListener {
public Main() {
super(new GridLayout(2,2));
final JTextArea jt= new JTextArea("dear test :) ",5,20);
FileReader reader = null;
System.err.println("Error closing reader");
exception.printStackTrace();
JButton bu = new JButton("copiar");
final Clipboard clipboard = getToolkit().getSystemClipboard();
//new add
add(nn);
add(tt);
bu.addMouseListener(new MouseListener() {
public void mouseEntered(MouseEvent e) {
StringSelection data = new StringSelection(jt.getText());
clipboard.setContents(data, data);
public void mouseClicked(MouseEvent e) {
public void mousePressed(MouseEvent e) {
public void mouseReleased(MouseEvent e) {
public void mouseExited(MouseEvent e) {
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("TextDemo");
public static void main(String[] args) {
//Schedule a job for the event dispatch thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
public void mouseClicked(MouseEvent e) {    }
public void mousePressed(MouseEvent e) {    }
public void mouseReleased(MouseEvent e) {    }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) {  }
}

Answer 1

import java.awt.;
import javax.swing.;
import java.awt.datatransfer.*;
import java.io.FileReader;
import java.io.IOException;
import java.awt.event.MouseListener;
import java.awt.event.MouseEvent;
public class Main extends JPanel implements MouseListener {
public Main() {
super(new GridLayout(2,2));
final JTextArea jt= new JTextArea("dear test :) ",5,20);
FileReader reader = null;
System.err.println("Error closing reader");
exception.printStackTrace();
JButton bu = new JButton("copiar");
final Clipboard clipboard = getToolkit().getSystemClipboard();
//new add
add(nn);
add(tt);
bu.addMouseListener(new MouseListener() {
public void mouseEntered(MouseEvent e) {
StringSelection data = new StringSelection(jt.getText());
clipboard.setContents(data, data);
public void mouseClicked(MouseEvent e) { }
public void mousePressed(MouseEvent e) { }
public void mouseReleased(MouseEvent e) {}
public void mouseExited(MouseEvent e) { }
private static void createAndShowGUI() {
//Create and set up the window.
JFrame frame = new JFrame("TextDemo");
public static void main(String[] args) {
//Schedule a job for the event dispatch thread:
//creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
public void mouseClicked(MouseEvent e) { }
public void mousePressed(MouseEvent e) { }
public void mouseReleased(MouseEvent e) { }
public void mouseEntered(MouseEvent e) { }
public void mouseExited(MouseEvent e) { }
} the problem is this line bu.addMouseListener(new MouseListener() {
if i change this to bu.addMouseListener(this() {
it gives error saying expected ')'
and then doesn't compile.
i just don't know why , although the program runs when i declare the methods two times,
but i think it's better java code , if i learn it why is this error and correct it