This is the solution to the Target problem from Assignment 2 of the Stanford CS106A Introduction to Programming Methodology Class

Target

/*
 * File: Target.java
 * Name: 
 * Section Leader: 
 * -----------------
 * This file is the starter file for the Target problem.
 */

import acm.graphics.*;
import acm.program.*;
import java.awt.*;

public class Target extends GraphicsProgram {	
	public void run() {
		putOuterCircle();
		putMiddleCircle();
		putInnerCircle();
	}
	private void putOuterCircle() {
		int radius = 72;
		int x = getWidth()/2 - radius/2;
		int y = getHeight()/2 - radius/2;
		GOval OuterCircle = new GOval (x, y, radius, radius);
		OuterCircle.setColor(Color.RED);
		OuterCircle.setFilled(true);
		OuterCircle.setFillColor(Color.RED);
		add(OuterCircle);
	}
	private void putMiddleCircle() {
		double radius = 72*64/100;
		double x = getWidth()/2 - radius/2;
		double y = getHeight()/2 - radius/2;
		GOval MiddleCircle = new GOval (x, y, radius, radius);
		MiddleCircle.setColor(Color.WHITE);
		MiddleCircle.setFilled(true);
		MiddleCircle.setFillColor(Color.WHITE);
		add(MiddleCircle);
	}
	private void putInnerCircle() {
		double radius = 72*3/10;
		double x = getWidth()/2 - radius/2;
		double y = getHeight()/2 - radius/2;
		GOval InnerCircle = new GOval (x, y, radius, radius);
		InnerCircle.setColor(Color.RED);
		InnerCircle.setFilled(true);
		InnerCircle.setFillColor(Color.RED);
		add(InnerCircle);
	}
}

Here's my code. By setting a max_circles constant, this program can be possibly extended to draw more circles with just a minor change on adding a calculation to determine each circle's radius which could be radius-=(radius/MAX_CIRCLES).

import acm.graphics.;
import acm.program.;
import java.awt.*;

public class Target2 extends GraphicsProgram {
private static final int MAX_CIRCLES=3;
private static final int PIXELS_PER_INCH=72;
public void run() {
/* Set Initial Radius */
double radius=1;
drawTarget(radius);

}
private void drawTarget(double radius){
    radius*=PIXELS_PER_INCH;

    for(int i=0; i<MAX_CIRCLES; i++){

        double x=(getWidth()/2)-radius;
        double y=(getHeight()/2)-radius;
        GOval circle=new GOval(x, y, 2*radius, 2*radius);
        circle.setFilled(true);
        if (i%2==0){
        circle.setColor(Color.RED);
        }
        else{
            circle.setColor(Color.WHITE);   
        }
        add(circle);
        radius-=0.35*PIXELS_PER_INCH;



    }
}

I am taking cs101 at staford. Need Need help with coding "image expressions excercises" -week 3