Question on calling a method in an child class

[Toshiro Hitsuguya]

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;

public abstract class BouncingDevice {
int x;
int y;
Color color;
int xDirection = 0;
int yDirection = 0;
final int SIZE = 20;

public BouncingDevice(int startX, int startY, Color startColor) {
        x = startX;
        y = startY;
        color = startColor;
    }
public void animate() {

	 // Move the center of the object each time we draw it
        x += xDirection;
        y += yDirection;

        // If we have hit the edge, reverse direction
        if (x - SIZE/2 <= 0 || x + SIZE/2 >= SimpleDraw.WIDTH) {
            xDirection = -xDirection;
        }
        if (y - SIZE/2 <= 0 || y + SIZE/2 >= SimpleDraw.HEIGHT) {
            yDirection = -yDirection;
        } 
}
	public void moveInDirection(int xIncrement, int yIncrement) {//This is the method I am trying to call
        	xDirection = xIncrement;
        	yDirection = yIncrement;
    		}
	
	
}

I am trying to call the moveInDirection method in this other class:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;

public class BouncingBall extends BouncingDevice {

public BouncingBall(int startX, int startY, Color startColor) {
	super(startX, startY, startColor);
	}
public void draw(Graphics2D surface) {
 // Draw the object
        surface.setColor(color);
        surface.fillOval(x - SIZE/2, y - SIZE/2, SIZE, SIZE);
        surface.setColor(Color.BLACK);
        surface.setStroke(new BasicStroke(3.0f));
        surface.drawOval(x - SIZE/2, y - SIZE/2, SIZE, SIZE);
	
	animate(); //This one works just fine for some reason
	}
	moveInDirection(xIncrement, yIncrement); //Trying to call the method here
	
}
        

Whenever, I try to call the method in my bouncing ball class, the constructor says "invalid method declaration; return type required". How can I fix it?

Thank You

[Ernest Friedman-Hill]

That call to moveInDirection() appears just after the closing brace of the draw() method, meaning it's not inside any method. A normal line of code, like a method call, can only appear inside a method in Java. Swap it with the line before it, and all will be well.

[Christophe Verré]

This is caused by a bad indentation. See my comments in the code.

public class BouncingBall extends BouncingDevice {

	public BouncingBall(int startX, int startY, Color startColor) {
		super(startX, startY, startColor);
	}
	public void draw(Graphics2D surface) {
	 // Draw the object
	        surface.setColor(color);
	        surface.fillOval(x - SIZE/2, y - SIZE/2, SIZE, SIZE);
	        surface.setColor(Color.BLACK);
	        surface.setStroke(new BasicStroke(3.0f));
	        surface.drawOval(x - SIZE/2, y - SIZE/2, SIZE, SIZE);
		
		animate();
		// }  // <-- extra bracket
		moveInDirection(xIncrement, yIncrement);  // <-- where do xIncrement, yIncrement come from ?
		
	}
} // <-- missing bracket

[Fred Hamilton]

two points...

1.perhaps I'm just stating the obvious, but this is a compile problem right? To state "Whenever I try to call" makes it sound like runtime.

2. Correct me if I'm wrong, but BouncingBall is a child of abstract class BouncingDevice. Isn't the child supposed to inherit the method from the parent, not call a method in the parent? And doesn't that make the "fixes" wrong? We should be fixing a bad declaration, not putting a call in the correct location.


Ok I have mistated point 2. The compiler sees this as an attempt to ovverride the method in the parent, and the programmer may not want to ovveride the method. But it still feels wrong to call a method in an abstract class, and doubly wrong to call a method in a parent from a child. It seems we should be referencing the method as being in BouncingBall, not from Bouncing ball. e.g. from some other class we would have...

BouncingBall bb = new BouncingBall().

...

bb.moveInDirection( dx, dy)

with no reference at all to moveInDirection with the class BouncingBall.