work with Box2D in libGDX with box2D manual
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i'm new in box2d and i want to work with it in libgdx. so i read manual of box2d and write it. but i get error. i don't know where is my problem. if someone know it plz help.

    public class Main implements ApplicationListener{
	/*** Creating a World ***/
	Vector2 gravity;
	boolean doSleep = true; 
	World world;
	BodyDef groundBodyDef;
	Body groundBody;
	PolygonShape groundBox;
	/*** Creating a World ***/
	
	/*** Creating a Dynamic Body ***/
	BodyDef bodyDef;
	Body body;
	PolygonShape dynamicBox;
	FixtureDef fixtureDef;
	/*** Creating a Dynamic Body ***/
	
	/*** Simulating the World (of Box2D) ***/
	float timeStep = 1 / 60;
	int velocityIterations = 6;
	int positionIterations = 2; 
	Vector2 position;
	float angle;
	/*** Simulating the World (of Box2D) ***/
	
	@Override
	public void create() {
		/*** Creating a World ***/
		gravity = new Vector2(0, -10);
		world = new World(gravity, doSleep);
		groundBodyDef = new BodyDef();
		groundBodyDef.position.set(0, -10);
		groundBody = world.createBody(groundBodyDef);
		groundBox.setAsBox(50, 10);
		groundBody.createFixture(groundBox, 0);
		/*** Creating a World ***/
		
		/*** Creating a Dynamic Body ***/
		bodyDef.type = BodyType.DynamicBody;
		bodyDef.position.set(240, 160);
		body = world.createBody(bodyDef);
		dynamicBox.setAsBox(1, 1);
		fixtureDef = new FixtureDef();
		fixtureDef.shape = dynamicBox;
		fixtureDef.density = 1;
		fixtureDef.friction = 0.3f;
		body.createFixture(fixtureDef);
		/*** Creating a Dynamic Body ***/
	}

	@Override
	public void render() {
		Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
		Gdx.gl.glClearColor(1, 1, 1, 1);
		
		/*** Simulating the World (of Box2D) ***/
		for (int i = 0; i < 60; i++) {
			world.step(timeStep, velocityIterations, positionIterations);
			position = body.getPosition();
			angle = body.getAngle();
			System.out.print("Output" + position.x + ", " + position.y + ", " + angle);
		}
		/*** Simulating the World (of Box2D) ***/
	}
}

i just read manual and write it. i think , i must add something else for libgdx, like camera or... . really i don't know.