Libgdx null Pointer - nullpointerexception

Question

I´m working on a Box2D Jump and run game and want the player to be teleported to the start when he hits a spike, but when he hits the spike, I get a null pointer exception.
Heres my Contact class:
public class WorldContactListener implements ContactListener {
Player player;
#Override
public void beginContact(Contact contact) {
Fixture fixA = contact.getFixtureA();
Fixture fixB = contact.getFixtureB();
player = new Player();
int cDef = fixA.getFilterData().categoryBits | fixB.getFilterData().categoryBits;
switch (cDef) {
case HardwareRunner.PLAYER_BIT | HardwareRunner.BRICK_BIT:
case HardwareRunner.PLAYER_BIT | HardwareRunner.SPIKE_BIT:
player.die();
}
}
And heres the part of my player class:
public void definePlayer(){
bdef.position.set(32 / runner.PPM, (6 * 32) / runner.PPM);
bdef.type = BodyDef.BodyType.DynamicBody;
b2body = world.createBody(bdef);
FixtureDef fdef = new FixtureDef();
PolygonShape shape = new PolygonShape();
Vector2[] vertice = new Vector2[4];
vertice[0] = new Vector2(-13, 13).scl(1 / runner.PPM);
vertice[1] = new Vector2(13, 13).scl(1 / runner.PPM);
vertice[2] = new Vector2(13, -13).scl(1 / runner.PPM);
vertice[3] = new Vector2(-13, -13).scl(1 / runner.PPM);
shape.set(vertice);
shape.getRadius();
fdef.filter.categoryBits = HardwareRunner.PLAYER_BIT;
fdef.filter.maskBits =
HardwareRunner.GROUND_BIT |
HardwareRunner.COIN_BIT |
HardwareRunner.BRICK_BIT |
HardwareRunner.ENEMY_BIT |
HardwareRunner.SPIKE_BIT |
HardwareRunner.ENEMY_HEAD_BIT |
HardwareRunner.ITEM_BIT;
fdef.shape = shape;
fdef.friction = .1f;
b2body.createFixture(fdef).setUserData(this);
fdef.isSensor = true;
b2body.createFixture(fdef).setUserData(this);
}
public void die() {
world.destroyBody(b2body);
bdef.position.set(32 / runner.PPM, (6 * 32) / runner.PPM);
bdef.type = BodyDef.BodyType.DynamicBody;
b2body = world.createBody(bdef);
FixtureDef fdef = new FixtureDef();
PolygonShape shape = new PolygonShape();
Vector2[] vertice = new Vector2[4];
vertice[0] = new Vector2(-13, 13).scl(1 / runner.PPM);
vertice[1] = new Vector2(13, 13).scl(1 / runner.PPM);
vertice[2] = new Vector2(13, -13).scl(1 / runner.PPM);
vertice[3] = new Vector2(-13, -13).scl(1 / runner.PPM);
shape.set(vertice);
shape.getRadius();
fdef.filter.categoryBits = HardwareRunner.PLAYER_BIT;
fdef.filter.maskBits =
HardwareRunner.GROUND_BIT |
HardwareRunner.COIN_BIT |
HardwareRunner.BRICK_BIT |
HardwareRunner.ENEMY_BIT |
HardwareRunner.SPIKE_BIT |
HardwareRunner.ENEMY_HEAD_BIT |
HardwareRunner.ITEM_BIT;
fdef.shape = shape;
fdef.friction = .1f;
b2body.createFixture(fdef).setUserData(this);
fdef.isSensor = true;
b2body.createFixture(fdef).setUserData(this);
}
And the error is:
Exception in thread "LWJGL Application" java.lang.NullPointerException
at de.tobls.hardwarerunner.Sprites.Player.die(Player.java:223)
at de.tobls.hardwarerunner.Tools.WorldContactListener.beginContact(WorldContactListener.java:27)
at com.badlogic.gdx.physics.box2d.World.beginContact(World.java:982)
at com.badlogic.gdx.physics.box2d.World.jniStep(Native Method)
at com.badlogic.gdx.physics.box2d.World.step(World.java:686)
at de.tobls.hardwarerunner.Screens.PlayScreen.update(PlayScreen.java:112)
at de.tobls.hardwarerunner.Screens.PlayScreen.render(PlayScreen.java:127)
at com.badlogic.gdx.Game.render(Game.java:46)
at de.tobls.hardwarerunner.HardwareRunner.render(HardwareRunner.java:71)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:215)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:120)
Can anyone help me?

Answer 1

First of all you should not destroy the worlds items in asynchronous methods - notice that contact listeners's methods are asynchronous.
The proper way to destroy the body od to mark it and then destroy right before world.update()
//in asynchronous method
body.setUserData("DESTROY");
//when rendering
for(Body body : world.getBodies())
if(body.getUserData().equals("DESTROY")) world.destroyBody(body);
But on the top of this - I see that you are doing nothing but moving the body when die so why not to use setTransform method then
body.setTransform(new Vector2(newX, newY), body.getAngle() );
Instead of removing body and creating it again in a new position