Question

java 方法声明无效，需要返回值

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class HelloJava
extends JComponent implements MouseMotionListner{

int messageX=125,messageY=95;
String theMessage;

public HelloJava2(String message){
theMessage=message;
addMouseMotionListener(this); 这里出错。
}

public void paintComponent(Graphics g){
g.drawString(theMessage,messageX,messageY);
}

public void mouseDragged(MouseEvent e){
messageX=e.getX();
messageY=e.getY();
repaint();
}

public void mouseMoved(MouseEvent e){}

public static void main(String[] args){
JFrame f=new JFrame("HelloJava2");
f.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent we){System.exit(0);}
});
f.setSize(300,300);
f.getContentPane().add(new HelloJava2("Hello,java!"));
f.setvisible(true);
}
}

Answer 1

把返回值设成void