java - How to differenciate instanciated variables from others? -

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this question has answer here:

here code:

        piece grille[][] = new piece[9][9];         grille[0][0] = new piece(1,joueur1,0);         grille[8][0] = new piece(1,joueur2,0);         grille[0][8] = new piece(1,joueur2,0);         grille[8][8] = new piece(1,joueur1,0);         grille[0][1] = new piece(3,joueur2,1);         grille[1][0] = new piece(3,joueur2,1);         grille[1][1] = new piece(3,joueur2,1);         grille[7][0] = new piece(3,joueur1,2);         grille[7][1] = new piece(3,joueur1,2);         grille[8][1] = new piece(3,joueur1,2);         grille[7][7] = new piece(3,joueur2,3);         grille[7][8] = new piece(3,joueur2,3);         grille[8][7] = new piece(3,joueur2,3);         grille[0][7] = new piece(3,joueur1,4);         grille[1][7] = new piece(3,joueur1,4);         grille[1][8] = new piece(3,joueur1,4);         grille[3][4] = new piece(2,joueur1,0);         grille[5][4] = new piece(2,joueur2,0);          for(int i=0; i<9; i++){             for(int j=0;j<9;j++){                 if(grille[i][j].joueur == null)                     grille[i][j] = new piece(0, null,0); //0 correspond case vide             }         }

my instance variables in piece :

public int type;     public joueur joueur; public int param;

it seems error comes this: grille[i][j].joueur == null

i error:

exception in thread "main" java.lang.nullpointerexception @ citadella.(citadella.java:35) @ partie.main(partie.java:8)

i think want if grille[i][j] == null instead of dereferencing joueur on it.


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