cant find the error , please help.

im getting this error:

Code:

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java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException
        at Map.<init>(Map.java:21)

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and i cant find the errors origen.
heres the code:

Code:

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import java.util.List;


public class Map {
        public
                Entity GLOBAL_ENTITY = new Entity();
                List<Entity> ents;
                char[][] map = new char[10][10];
        private
                int x,y,i;
       
        public Map()
        {
                for(x = 0; x < 10; x++)
                {
                        for(y = 0; y < 10; y++)
                        {
                                map[x][y] = '*';
                        }
                }
                ents.add(GLOBAL_ENTITY.add());
        }
        public void DrawMap(List<Entity> el)
        {
                for(i = 0; i < el.size();i++)
                {
                        for(x = 0; x < 10; x++)
                        {
                                for(y = 0; y < 10; y++)
                                {
                                        map[x][y] = el.get(i).draw_char;
                                }
                        }
                }
        }
}

---

Code:

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//import java.util.*;

public class Entity {
        public
                Vector vector = new Vector();
                static int count;
                int id;
                final char draw_char = 'e';
        public void Entitty()
        {
                count++;
                id = count;
        }
        public void MoveDir(int ar)
        {
                switch(ar)
                {
                        case 0:
                                vector.x -=1;
                                break;
                               
                        case 1:
                                vector.y -=1;
                                break;
                       
                        case 2:
                                vector.x +=1;
                                break;
                       
                        case 3:
                                vector.y +=1;
                                break;
                       
                        default:
                                System.out.printf("Illigal argument. use 0 , 1, 2 , 3");
                                break;
                }
        }
       
        public Entity add()
        {
                Entity re = new Entity();
                return(re);
        }
}

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Which line is throwing the error? (line 21 in your Map class) That's the first place to start. And where's the code where you create a Map object and call its methods such as DrawMap(...)?

edit other recommendations: Please learn the Java naming conventions. To keep things consistent and thus easier to understand, you'll want to start method names with a lower case letter and classes with an upper case letter. Also, you may wish to rename your Map class to another name, something that isn't already part of the standard Java library.

Luck!

See my comments in your code:

Code:

---

import java.util.List;


public class Map {
        public
                Entity GLOBAL_ENTITY = new Entity();
                List<Entity> ents; // <--- not initialized so its null
                char[][] map = new char[10][10];
        private
                int x,y,i;
       
        public Map()
        {
                for(x = 0; x < 10; x++)
                {
                        for(y = 0; y < 10; y++)
                        {
                                map[x][y] = '*';
                        }
                }
                          // you can't add anything to ents (it's null)
                ents.add(GLOBAL_ENTITY.add());
        }

---

kind regards,

Jos

Code:

---

public class Mother {
       
        public
                static int[][] draw_map = new int[10][10];
                static int i , j;
                static final int LEFT = 0;
                static final int UP = 1;
                static final int RIGHT = 2;
                static final int DOWN = 3;
                static Entity ent1 = new Entity();
                static Map map1 = new Map();
       
        public static void main(String[] args) {
                InitMap();
                map1.DrawMap(map1.ents);
        }
       
        public static void InitMap()
        {
                for(i = 0; i <10; i++)
                {
                        for(j = 0; j <10; j++)
                        {
                                draw_map[i][j] = 0;
                        }
                }
        }

}

---

please note that Map is a name for an Interface in Java and it's not a good idea to name your class Map. inside the class Entity you are instantiating a class with new Vector(). even if you make an import with java.util.Vector the code produces errors because the variables x and y used in the code are not fields of the class Vector.

Quote:

---

Originally Posted by JosAH

See my comments in your code:

Code:

---

import java.util.List;


public class Map {
        public
                Entity GLOBAL_ENTITY = new Entity();
                List<Entity> ents; // <--- not initialized so its null
                char[][] map = new char[10][10];
        private
                int x,y,i;
       
        public Map()
        {
                for(x = 0; x < 10; x++)
                {
                        for(y = 0; y < 10; y++)
                        {
                                map[x][y] = '*';
                        }
                }
                          // you can't add anything to ents (it's null)
                ents.add(GLOBAL_ENTITY.add());
        }

---

kind regards,

Jos

---

then how do i initialize it?

Quote:

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Originally Posted by TheBreadCat

then how do i initialize it?

---

assign it an object using new XXXXX(). In this case since List is an interface not a class, you can't do = new List<Entity>();, but you can use new ArrayList<Entity>() or LinkedList whichever you feel is best. I do find it strange that you are using a second class and directly accessing your Map's fields to pass into a Map method. If Map is going to be calling code on its own field, why the need for an outside class to pass the field back in? Again it seems strange.

Quote:

---

Originally Posted by JosAH

See my comments in your code:

Code:

---

import java.util.List;


public class Map {
        public
                Entity GLOBAL_ENTITY = new Entity();
                List<Entity> ents; // <--- not initialized so its null
                char[][] map = new char[10][10];
        private
                int x,y,i;
       
        public Map()
        {
                for(x = 0; x < 10; x++)
                {
                        for(y = 0; y < 10; y++)
                        {
                                map[x][y] = '*';
                        }
                }
                          // you can't add anything to ents (it's null)
                ents.add(GLOBAL_ENTITY.add());
        }

---

kind regards,

Jos

---

Quote:

---

Originally Posted by j2me64

please note that Map is a name for an Interface in Java and it's not a good idea to name your class Map. inside the class Entity you are instantiating a class with new Vector(). even if you make an import with java.util.Vector the code produces errors because the variables x and y used in the code are not fields of the class Vector.

---

renamed Vector to Vector2d and Map to Wolrd.

Quote:

---

Originally Posted by TheBreadCat

then how do i initialize it?

---

Pick your choice:

Code:

---

List<Entity> ents= new ArrayList<Entity>();

---

or:

Code:

---

List<Entity> ents= new LinkedList<Entity>();

---

b.t.w. you posted another piece of code without any comments; what do these two pieces of code have to do with eachother?

kind regards,

Jos

For instance you have the code below (please see comments):

Code:

---

public class Mother {

  //....

  static Map map1 = new Map();  // create a new Map object

  //....

  public static void main(String[] args) {
      InitMap();
      map1.DrawMap(map1.ents); // you call Map's DrawMap method passing it's own field, ents back into it.
  }

  //....
}

---

Code:

---

class Map {
  //...
    List<Entity> ents;
  //...

  //...

  public void DrawMap(List<Entity> el) {
      for (i = 0; i < el.size(); i++) {
        for (x = 0; x < 10; x++) {
            for (y = 0; y < 10; y++) {
              map[x][y] = el.get(i).draw_char;
            }
        }
      }
  }
}

---

Rather, wouldn't it make more sense to just have Map make its method call with its own field:

Code:

---

public class Mother {

  //....

  static Map map1 = new Map(); 

  //....

  public static void main(String[] args) {
      InitMap();
      map1.DrawMap(); // call DrawMap without parameter
  }

  //....
}

---

Code:

---

class Map {
  //...
    List<Entity> ents;
  //...

  //...

  public void DrawMap() {
      for (i = 0; i < ents.size(); i++) { // *** call code here with the internal field itself
        for (x = 0; x < 10; x++) {
            for (y = 0; y < 10; y++) {
              map[x][y] = ents.get(i).draw_char;
            }
        }
      }
  }
}

---

Quote:

---

Originally Posted by Fubarable

For instance you have the code below (please see comments):

Code:

---

public class Mother {

  //....

  static Map map1 = new Map();  // create a new Map object

  //....

  public static void main(String[] args) {
      InitMap();
      map1.DrawMap(map1.ents); // you call Map's DrawMap method passing it's own field, ents back into it.
  }

  //....
}

---

Code:

---

class Map {
  //...
    List<Entity> ents;
  //...

  //...

  public void DrawMap(List<Entity> el) {
      for (i = 0; i < el.size(); i++) {
        for (x = 0; x < 10; x++) {
            for (y = 0; y < 10; y++) {
              map[x][y] = el.get(i).draw_char;
            }
        }
      }
  }
}

---

Rather, wouldn't it make more sense to just have Map make its method call with its own field:

Code:

---

public class Mother {

  //....

  static Map map1 = new Map(); 

  //....

  public static void main(String[] args) {
      InitMap();
      map1.DrawMap(); // call DrawMap without parameter
  }

  //....
}

---

Code:

---

class Map {
  //...
    List<Entity> ents;
  //...

  //...

  public void DrawMap() {
      for (i = 0; i < ents.size(); i++) { // *** call code here with the internal field itself
        for (x = 0; x < 10; x++) {
            for (y = 0; y < 10; y++) {
              map[x][y] = ents.get(i).draw_char;
            }
        }
      }
  }
}

---

---

YAY the problem is solved!
or..

Code:

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java.lang.NoClassDefFoundError: Mother
Caused by: java.lang.ClassNotFoundException: Mother
        at java.net.URLClassLoader$1.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
Exception in thread "main"

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O.o

so what to do?

Quote:

---

Originally Posted by TheBreadCat

so what to do?

---

Compile your Mother class and make the classpath point to the correct directory. (even better for now: recompile all your Java files)

kind regards,

Jos

Quote:

---

Originally Posted by JosAH

make the classpath point to the correct directory.

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how?(im using eclipse)