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Thread: NullPointerException?

  1. #1
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    Default NullPointerException?

    I've got a lot of code, and I'm not entirely sure what I've done wrong. My IDE isn't showing any errors, but I've got NullPointerExceptions in three of my classes.

    What should I do?

    Exception in thread "main" java.lang.NullPointerException
    at rpgtxt.Player.getBlock(Player.java:71)
    at rpgtxt.Battle.mAttack(Battle.java:59)
    at rpgtxt.Battle.bMain(Battle.java:14)
    at rpgtxt.Main.main(Main.java:83)
    Player Class :

    package rpgtxt;
    import java.util.*;
     
    public class Player {
     
    	public int hp;
    	public int hptotal;
    	public int dmg;
    	public int str;
    	public int intlg;
    	public int will;
    	public int xp;
    	public int lvl;
    	public int block;
    	public String pCls;
    	public boolean isAlive;
     
    	public String pName()
    	{
    		Scanner scn = new Scanner(System.in);
    		String ans = scn.nextLine();
    		ans = pCls;
    		return ans;
    	}
     
    	public String pClass()
    	{
    		Scanner scn = new Scanner(System.in);
    		String ans = scn.nextLine();
    		return ans;
    	}
     
    	public int getHP()
    	{
    		hp = getLVL() * 25;
    		return hp;
    	}
     
    	public int getLVL()
    	{
    		int xp_total = xp;
    		if (xp_total >= 110000)
    		{
    			lvl = 5;
    			return lvl;
    		}
    		else if (xp_total >= 75000)
    		{
    			lvl = 4;
    			return lvl;
    		}
    		else if (xp_total >= 45000)
    		{
    			lvl = 3;
    			return lvl;
    		}
    		else if (xp_total >= 20000)
    		{
    			lvl = 2;
    			return lvl;
    		}
    		else
    		{
    			lvl = 1;
    			return lvl;
    		}
     
    	}
     
    	public int getBlock()
    	{
    		if (pCls.equalsIgnoreCase("Warrior"))
    		{
    			block = str - 10;
    		}
    		else if (pCls.equalsIgnoreCase("Rogue"))
    		{
    			block = will - 10;
    		}
    		else if (pCls.equalsIgnoreCase("Wizard"))
    		{
    			block = intlg - 10;
    		}
     
    		return block;
    	}
     
     
     
    }

    Main Class:

    package rpgtxt;
    import java.util.*;
     
    public class Main {
     
    	public static void main(String[] args)
    	{
    		Scanner in = new Scanner(System.in);
    		Player player = new Player();
    		int lvldsp = player.getLVL();
    		System.out.println("Hello. What's your name?");
    		String Name;
    		Name = player.pName();
    		System.out.println("Ah... " +Name+ ". Are you a rogue, warrior, or wizard?");
    		String Class = player.pClass();
    		int clsslct = 1;
    		while (clsslct == 1)
    		{
    			if (Class.equalsIgnoreCase("Rogue"))
    			{
    				player.str = 5;
    				player.intlg = 10;
    				player.will = 15;
    				clsslct--;
    			}
    			else if (Class.equalsIgnoreCase("Wizard"))
    			{
    				player.str = 5;
    				player.intlg = 15;
    				player.will = 10;
    				clsslct--;
    			}
    			else if (Class.equalsIgnoreCase("Warrior"))
    			{
    				player.str = 15;
    				player.intlg = 5;
    				player.will = 10;
    				clsslct--;
    			}
     
    		}
    		System.out.println("The path of the " +Class+ " is a noble one.");
     
    		if (Class.equalsIgnoreCase("Warrior"))
    		{
    			System.out.println("Here's a sword.");
    			System.out.println("You received: Wooden Sword! Str + 1");
    			Item wsword = new Item();
    			wsword.iStr = 1;
    			player.dmg = 1 + wsword.iStr + player.str;
    			wsword.iName = "Wooden Sword";
    			System.out.println("Your damage is now "+player.dmg);
    		}
    		else if (Class.equalsIgnoreCase("Rogue"))
    		{
    			System.out.println("Here are two daggers.");
    			System.out.println("You received: Wooden Daggers! Will + 1");
    			Item wdags = new Item();
    			wdags.iWil = 1;
    			player.dmg = 1 + wdags.iWil + player.will;
    			wdags.iName = "Wooden Daggers";
    			System.out.println("Your damage is now "+player.dmg);
    		}
    		else if (Class.equalsIgnoreCase("Wizard"))
    		{
    			System.out.println("Here's a staff.");
    			System.out.println("You received: Wooden Staff! Int + 1");
    			Item wstaff = new Item();
    			wstaff.iInt = 1;
    			player.dmg =  1 + wstaff.iInt + player.intlg;
    			wstaff.iName = "Wooden Staff";
    			System.out.println("Your damage is now "+player.dmg);
    		}
     
    		System.out.println("Now that you have a weapon, are you prepared for your first battle?");
    		String fBattle;
    		fBattle = in.nextLine();
    		if (fBattle.equalsIgnoreCase("yes"))
    		{
    			Monster fMon = new Monster();
    			fMon.mName = "Zombie";
    			Battle rBattle = new Battle();
    			rBattle.bMain(player, fMon);
    		}
     
     
    		if (player.isAlive = false)
    		{
    			System.out.println("Game over!");
    		}
    	}
     
    }

    Battle Class:

    package rpgtxt;
    import java.util.*;
     
    public class Battle {
     
    	public void bMain(Player player, Monster monster)
    	{
    		Scanner keyIn = new Scanner(System.in);
    		System.out.println("A " +monster.mName+ " has attacked!");	
    		do
    		{
    			wrAttack(player, monster);
    			keyIn.nextLine();
    			mAttack(player, monster);
     
    		} while(player.hp > 0 && monster.hp > 0);
     
    	}
     
    	public void wrAttack(Player player, Monster monster)
    	{
    		Scanner keyIn = new Scanner(System.in);
    		System.out.println("You attack!");
    		Random roll = new Random();
    		int rvalue = roll.nextInt( 21 );
    		int mBlock = monster.getBlock(player);
    		System.out.println(monster.mName+" has "+monster.hp+" hp.");
    		keyIn.nextLine();
    		if (rvalue == 20)
    		{
    			System.out.println("Critical hit!");
    			monster.hp = monster.hp - (player.dmg * 2);
    			System.out.println(monster.mName+" has "+monster.hp+" hp.");
    			player.xp = player.xp + 1000;
    			keyIn.nextLine();
    		}
    		else if (rvalue > mBlock)
    		{
    			System.out.println("You strike!");
    			monster.hp = monster.hp - player.dmg;
    			System.out.println(monster.mName+" has "+monster.hp+" hp.");
    			player.xp = player.xp + 500;
    			keyIn.nextLine();
    		}
    		else if (rvalue < mBlock)
    		{
    			System.out.println("You miss!");
    			keyIn.nextLine();
    		}
     
    	}
     
    	public void mAttack(Player player, Monster monster)
    	{
    		Scanner keyIn = new Scanner(System.in);
    		System.out.println(monster.mName+" attacks!");
    		Random roll = new Random();
    		int rvalue = roll.nextInt( 21 );
    		int block = player.getBlock();
    		System.out.println("You have "+player.hp+" hp.");
    		keyIn.nextLine();
    		if (rvalue == 20)
    		{
    			System.out.println("Critical hit!");
    			player.hp = player.hp - (monster.dmg * 2);
    			System.out.println("You have "+player.hp+" hp.");
    			keyIn.nextLine();
    		}
    		else if (rvalue > block)
    		{
    			System.out.println(monster.mName+" strikes!");
    			player.hp = player.hp - monster.dmg;
    			System.out.println("You have "+player.hp+" hp.");
    			keyIn.nextLine();
    		}
    		else if (rvalue < block)
    		{
    			System.out.println(monster.mName+" misses!");
    			keyIn.nextLine();
    		}
    	}
    }

    Any help is appreciated!


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: NullPointerException?

    Exception in thread "main" java.lang.NullPointerException
    at rpgtxt.Player.getBlock(Player.java:71)
    at rpgtxt.Battle.mAttack(Battle.java:59)
    at rpgtxt.Battle.bMain(Battle.java:14)
    at rpgtxt.Main.main(Main.java:83)
    You read the stack trace in the error message starting at the bottom:
    code at line 83 called the bMain() method
    code at line 14 called the mAttack() method
    code at line 59 called the getBlock() method
    At line 71 there was a variable with a null value.

    To fix the problem, look at line 71, find the variable that had the null value and backtrack in the code to see why that variable did not have a valid value.
    If you don't understand my answer, don't ignore it, ask a question.

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