Circle.java

package examples.git;

public class Circle {
	private int x;
	private int y;
	
	public Circle (int x, int y) {
		this.x = x;
		this.y = y;
	}
    	
	public void printCoordinates() {
		System.out.println("coordinates: x = " + this.x + " y = " + this.y);
	}
	
	public int getX() {
		return x;
	}
	
	public void setX(int x) {
		this.x = x;
	}

	public int getY() {
		return y;
	}

	public void setY(int y) {
		this.y = y;
	}
	
}

CircleMover.java

package examples.git;

public class CircleMover {
	
	//the reference to the object circle is passed by value and cannot be changed!!
	/* moves the circle to x + deltaX, y + deltaY */
	public void moveCircle(Circle circle, int deltaX, int deltaY) {
        circle.setX(circle.getX() + deltaX);
        circle.setY(circle.getY() + deltaY);
    	
        //code that tries to assign a new reference to circle
        circle = new Circle(0, 0);
        circle = null;
    }

}

ReferenceValueTest.java

package examples.git.tests;

import examples.git.*;
import junit.framework.TestCase;

public class ReferenceValueTest extends TestCase {

	public void testModifiedString() {
		String originalString = "first string";
		int originalNumber = 10;
		StringModifier test = new StringModifier(originalString, originalNumber);
		String beforeMethodOne = test.string + " " + test.number;
		System.out.println(beforeMethodOne);
		StringModifier.methodOne(test.string, test.number);
		String afterMethodOne = test.string + " " + test.number;
		System.out.println(afterMethodOne);

		assertEquals(afterMethodOne, beforeMethodOne);
		
	}
	
	
	public void testMoveCircle() {
		int origin = 0;
		Circle myCircle = new Circle(origin, origin);
		int delta = 10;
		myCircle.printCoordinates();
		CircleMover circleMover = new CircleMover();
		circleMover.moveCircle(myCircle, delta, delta);
		myCircle.printCoordinates();
		
		assertEquals(origin + delta, myCircle.getX());
		assertEquals(origin + delta, myCircle.getY());
	}

	
	

}

StringModifier.java

package examples.git;

public class StringModifier {
	
	public String string;
	public int number;
	
	public StringModifier(String string, int number) {
		this.string = string;
		this.number = number;
	}
	
	public static void methodOne(String s, int number) {
		s = "string modified by methodOne";
		number = 0;
	}

}