declare and initialize variables in java

Question

this code is for craps game (Deitel java how to program)

why myPoint variable needs to be initialize and if not a compilation error will occur???

i mean if there is win or loss in first roll there is no need to initialize mypoint (because it is not being use anymore)

and if there is no win or loss in first roll, myPoint gets value in switch default label

import java.util.Random;

public class Craps 
{
   // create random number generator for use in method rollDice
   private static final Random randomNumbers = new Random(); 

   // enumeration with constants that represent the game status
   private enum Status { CONTINUE, WON, LOST };

   // constants that represent common rolls of the dice
   private static final int SNAKE_EYES = 2;
   private static final int TREY = 3;
   private static final int SEVEN = 7;
   private static final int YO_LEVEN = 11;
   private static final int BOX_CARS = 12;

   // plays one game of craps
   public static void main( String[] args )
   {
      int myPoint = 0; // point if no win or loss on first roll
      Status gameStatus; // can contain CONTINUE, WON or LOST

      int sumOfDice = rollDice(); // first roll of the dice

      // determine game status and point based on first roll 
      switch ( sumOfDice ) 
      {
         case SEVEN: // win with 7 on first roll
         case YO_LEVEN: // win with 11 on first roll           
            gameStatus = Status.WON;
            break;
         case SNAKE_EYES: // lose with 2 on first roll
         case TREY: // lose with 3 on first roll
         case BOX_CARS: // lose with 12 on first roll
            gameStatus = Status.LOST;
            break;
         default: // did not win or lose, so remember point         
            gameStatus = Status.CONTINUE; // game is not over
            myPoint = sumOfDice; // remember the point
            System.out.printf( "Point is %d\n", myPoint );
            break; // optional at end of switch
      } // end switch 

      // while game is not complete
      while ( gameStatus == Status.CONTINUE ) // not WON or LOST
      { 
         sumOfDice = rollDice(); // roll dice again

         // determine game status
         if ( sumOfDice == myPoint ) // win by making point
            gameStatus = Status.WON;
         else 
            if ( sumOfDice == SEVEN ) // lose by rolling 7 before point
               gameStatus = Status.LOST;
      } // end while 

      // display won or lost message
      if ( gameStatus == Status.WON )
         System.out.println( "Player wins" );
      else
         System.out.println( "Player loses" );
   } // end main

   // roll dice, calculate sum and display results
   public static int rollDice()
   {
      // pick random die values
      int die1 = 1 + randomNumbers.nextInt( 6 ); // first die roll
      int die2 = 1 + randomNumbers.nextInt( 6 ); // second die roll

      int sum = die1 + die2; // sum of die values

      // display results of this roll
      System.out.printf( "Player rolled %d + %d = %d\n", 
         die1, die2, sum );

      return sum; // return sum of dice
   } // end method rollDice
} // end class Craps

Answer 1

You need to initialize myPoint because not all paths through the code that lead to the first use of the variable (i.e. the sumOfDice == myPoint inside an if) make an assignment to myPoint.

Specifically, this would happen if sumOfDice is equal to any value that falls outside the default case of the switch statement.

Unlike member variables that are default-initialized, local variables need to be initialized explicitly. If the compiler finds a path where an unassigned variable is used, it produces an error.