What does synchronized()/wait()/notifyAll() do in Java?

Possible Duplicate:
Java Synchronization

I'm reading the book Beginning Android Games.

It uses synchronized() a lot but I don't really understand what it does. I haven't used Java in a long time and I'm not sure if I ever used multithreading.

In the Canvas examples it uses synchronized(this). However in the OpenGL ES example, it creates an Object called stateChanged and then uses synchronized(stateChanged). When the game state changes it calls stateChanged.wait() and then stateChanged.notifyAll();

Some code:

    Object stateChanged = new Object();

    //The onPause() looks like this:
    public void onPause()
        {
            synchronized(stateChanged)
            {
                if(isFinishing())
                    state = GLGameState.Finished;
                else
                    state = GLGameState.Paused;

                while(true)
                {
                    try
                    {
                        stateChanged.wait();
                        break;
                    } catch(InterruptedException e)
                    {
                    }
                }
            }
        }
//The onDrawSurface looks like this:
public void onDrawFrame(GL10 gl)
    {
        GLGameState state = null;
        synchronized(stateChanged)
        {
            state = this.state;
        }

        if(state == GLGameState.Running)
        {

        }

        if(state == GLGameState.Paused)
        {
            synchronized(stateChanged)
            {
                this.state = GLGameState.Idle;
                stateChanged.notifyAll();
            }
        }

        if(state == GLGameState.Finished)
        {
            synchronized(stateChanged)
            {