public class Singleton
{
	private static Singleton theInstance = null;
	private Singleton() {}
	
	public static Singleton Instance()
	{
		if (theInstance == null)
			theInstance = new Singleton();
		return theInstance;	
	}
}

import junit.framework.*;
import java.lang.reflect.Constructor;

public class TestSimpleSingleton extends TestCase
{
	public TestSimpleSingleton(String name)
	{
		super(name);
	}
	
	public void testCreateSingleton()
	{
		Singleton s = Singleton.Instance();
		Singleton s2 = Singleton.Instance();
		assertSame(s, s2);
	}
	
	public void testNoPublicConstructors() throws Exception
	{
		Class singleton = Class.forName("Singleton");
		Constructor[] constructors = singleton.getConstructors();
		assertEquals("Singleton has public constructors.", 0, constructors.length);
	}
}

public class Monostate
{
	private static int itsX = 0;
	public Monostate() {}
	
	public void setX(int x)
	{
		itsX = x;
	}
	
	public int getX()
	{
		return itsX;
	}
}

import junit.framework.*;

public class TestMonostate extends TestCase
{
	public TestMonostate(String name)
	{
		super(name);
	}
	
	public void testInstance()
	{
		Monostate m = new Monostate();
		for (int x = 0; x<10; x++)
		{
			m.setX(x);
			assertEquals(x, m.getX());
		}
	}
	
	public void testInstancesBehaveAsOne()
	{
		Monostate m1 = new Monostate();
		Monostate m2 = new Monostate();

		for (int x = 0; x<10; x++)
		{
			m1.setX(x);
			assertEquals(x, m2.getX());
		}
	}
}