java.lang.NullPointerException

 at Slime1.checkKeyPress(Slime1.java:75)

 at Slime1.act(Slime1.java:41)

 at greenfoot.core.Simulation.actActor(Simulation.java:604)

 at greenfoot.core.Simulation.runOneLoop(Simulation.java:562)

 at greenfoot.core.Simulation.runContent(Simulation.java:221)

 at greenfoot.core.Simulation.run(Simulation.java:211)

public void checkKeyPress()

 {

 if(!isAttacking && Greenfoot.isKeyDown("x"))

 {

 setImage(attack1);

 attackTimer++;

 }

 if(!isAttacking && getImage().equals(attack1) && attackTimer == 1)

 {

 setImage(attack2);

 isAttacking = true;

 }

 if(isAttacking && !Greenfoot.isKeyDown("x"))

 {

 setImage(idle1);

 isAttacking = false;

 attackTimer = 0;

 } 

 }

}

import greenfoot.*; // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

public class Slime1 extends Player

{

 private GreenfootImage idle1;

 private GreenfootImage idle2;

 private GreenfootImage idle3;

 private GreenfootImage attack1;

 private GreenfootImage attack2;

 private GreenfootImage attack3; 

 private boolean isAttacking;

 private int attackTimer;



 public Slime1()

 {

 GreenfootImage idle1 = new GreenfootImage("stand1.png");

 GreenfootImage idle2 = new GreenfootImage("stand2.png");

 GreenfootImage idle3 = new GreenfootImage("stand3.png");

 GreenfootImage attack1 = new GreenfootImage("attack1.png");

 GreenfootImage attack2 = new GreenfootImage("attack2.png");

 GreenfootImage attack3 = new GreenfootImage("attack3.png");

 boolean isAttacking = false;

 int attackTimer = 0;

 } 

 public void act() 

 {

 checkKeyPress();

 }

 public void idleAnim()

 {

 try 

 {

 if (getImage().equals(idle1)) { 

 setImage (idle2);

 Thread.sleep(200);

 }

 if (getImage().equals(idle2)) { 

 setImage (idle3);

 Thread.sleep(200);

 }

 else { 

 setImage (idle1);

 Thread.sleep(200);

 }

 } catch (InterruptedException e) {

 // Handle here

 } 

 } 

 public void checkKeyPress()

 {

 if(!isAttacking && Greenfoot.isKeyDown("x"))

 {

 setImage(attack1);

 attackTimer++;

 }

 if(!isAttacking && getImage().equals(attack1) && attackTimer == 1)

 {

 setImage(attack2);

 isAttacking = true;

 }

 if(isAttacking && !Greenfoot.isKeyDown("x"))

 {

 setImage(idle1);

 isAttacking = false;

 attackTimer = 0;

 } 

 }

}