import org.jbox2d.dynamics.joints.ConstantVolumeJointDef; //导入依赖的package包/类
@Override
public void init(RunConfig config) throws InvalidTestFormatException {
	super.init(config);

	Vec2 gravity = new Vec2(0.0f, -10.0f);
	world = new World(gravity);

	ConstantVolumeJointDef constantVolumeJointDef = new ConstantVolumeJointDef();

	float cx = 0.0f;
	float cy = 10.0f;
	float rx = 5.0f;
	float ry = 5.0f;
	int n = 20;
	float circleRadius = 0.5f;
	for (int i = 0; i < n; ++i) {
		float angle = MathUtils.map(i, 0, n, 0, 2 * (float) Math.PI);
		BodyDef circleBodyDef = new BodyDef();
		circleBodyDef.fixedRotation = true;

		float x = cx + rx * (float) Math.sin(angle);
		float y = cy + ry * (float) Math.cos(angle);
		circleBodyDef.position.set(new Vec2(x, y));
		circleBodyDef.type = BodyType.DYNAMIC;
		Body circle = world.createBody(circleBodyDef);

		FixtureDef circleFixtureDef = new FixtureDef();
		CircleShape cd = new CircleShape();
		cd.m_radius = circleRadius;
		circleFixtureDef.shape = cd;
		circleFixtureDef.density = 1.0f;
		circle.createFixture(circleFixtureDef);
		constantVolumeJointDef.addBody(circle);
	}

	constantVolumeJointDef.frequencyHz = 10.0f;
	constantVolumeJointDef.dampingRatio = 1.0f;
	constantVolumeJointDef.collideConnected = false;
	world.createJoint(constantVolumeJointDef);

	BodyDef bodyDef2 = new BodyDef();
	bodyDef2.type = BodyType.DYNAMIC;
	PolygonShape psd = new PolygonShape();
	psd.setAsBox(3.0f, 1.5f, new Vec2(cx, cy + 15.0f), 0.0f);
	bodyDef2.position = new Vec2(cx, cy + 15.0f);
	fallingBox = world.createBody(bodyDef2);
	fallingBox.createFixture(psd, 1.0f);

	Body ground = null;
	PolygonShape sd = new PolygonShape();
	sd.setAsBox(50.0f, 0.4f);

	BodyDef bodyDef = new BodyDef();
	bodyDef.position.set(0.0f, 0.0f);
	ground = world.createBody(bodyDef);
	ground.createFixture(sd, 0f);

	sd.setAsBox(0.4f, 50.0f, new Vec2(-10.0f, 0.0f), 0.0f);
	ground.createFixture(sd, 0f);
	sd.setAsBox(0.4f, 50.0f, new Vec2(10.0f, 0.0f), 0.0f);
	ground.createFixture(sd, 0f);
}