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instantiating array objects

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Join Date: Jan 2009

Posts: 43

Reputation: scias23 is an unknown quantity at this point

Solved Threads: 0

scias23

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Light Poster

instantiating array objects

Sep 5th, 2009

i have this code.

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
      numberPlayers = 2;
      players = new Player[numberPlayers];
      setName();
      setHand();
 
    private static void setName() {
        for(int i=0;i<numberPlayers;i++) {
            out.print("Player "+ i + " name: ");
            players[i].setName(in.nextLine());
            out.println();
        }
    }
 
    private static void setHand() {
        for(int i=0;i<numberPlayers;i++) {
            out.print("Player "+ i+1 + " hand: ");
            players[i].setName(in.nextLine());
            out.println();
        }
    }
      numberPlayers = 2;
      players = new Player[numberPlayers];
      setName();
      setHand();

    private static void setName() {
        for(int i=0;i<numberPlayers;i++) {
            out.print("Player "+ i + " name: ");
            players[i].setName(in.nextLine());
            out.println();
        }
    }

    private static void setHand() {
        for(int i=0;i<numberPlayers;i++) {
            out.print("Player "+ i+1 + " hand: ");
            players[i].setName(in.nextLine());
            out.println();
        }
    }

but this gives me error:

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ROCK-PAPER-SCISSORS GAME
NOTE: hand input will loop until user(s) input(s) valid hand values
VALID HANDS: R-Rock, P-Paper, S-Scissors

Select your option below:

[1] Player vs Player
[2] Player vs Computer 1
Exception in thread "main" java.lang.NullPointerException
at RPS2.Game.setName(Game.java:61)
at RPS2.Game.main(Game.java:37)
Player 0 name: Java Result: 1

what's wrong? i want to instantiate an array object named Player with two elements.

a joke.

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Join Date: Feb 2006

Posts: 2,402

Reputation: masijade has much to be proud of

Solved Threads: 256

masijade

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Nearly a Posting Maven

Re: instantiating array objects

Sep 5th, 2009

Initiating an array simply creates "holding spaces" for the elements. Each of those elements is, however, currently "null". If you expect to have a "Player" predefined at every element, then you need to loop over the array and create one in each spot. i.e.

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
String[] array = new String[5];
for (int i = 0; i < array.length; i++) {
  array[i] = "";
}
String[] array = new String[5];
for (int i = 0; i < array.length; i++) {
  array[i] = "";
}

Edit: The default values for the array elements are as follows:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
boolean[] --> false
int[], short[], float[], double[], long[], char[], byte[] --> 0
Object[] --> null
boolean[] --> false
int[], short[], float[], double[], long[], char[], byte[] --> 0
Object[] --> null

Last edited by masijade; Sep 5th, 2009 at 4:15 am.

Java Programmer and Sun Systems Administrator

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