声明和初始化在java中
变量这段代码是胡扯游戏(java的Deitel公司如何编程)声明和初始化在java中
为什么myPoint变量需要初始化,如果没有会发生编译错误???
我的意思是如果有赢或第一卷损失有没有需要初始化mypoint(因为它没有被使用了)
而且如果在第一卷没有输赢,myPoint得值在开关默认标签
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
需要初始化myPoint
因为不是通过代码,导致第一次使用的变量(即sumOfDice == myPoint
的if
内)的所有路径进行分配,以myPoint
。
特别是,如果sumOfDice
等于落在外的default
情况下,switch
声明的任何值会发生这种事。
与默认初始化的成员变量不同,局部变量需要显式初始化。如果编译器找到使用未分配变量的路径,则会产生错误。
你的意思是即使是没有被使用的局部变量,它们也必须初始化? –
@hamid_c如果你不使用局部变量,你不必初始化它。但是如果你可以在某些情况下使用你的局部变量,它必须被初始化。 – dasblinkenlight
Java中的局部变量是在堆栈上创建的。在运行时,它不知道该内存位置是什么,所以这被认为是“垃圾”。编译器/运行时不初始化局部变量,只有实例(和静态)。
这就是为什么你总是在需要初始化你的Java本地变量。如果不是这样,编译器会发出抱怨
这在任何Java教程中都有介绍。 –