java嵌套if语句else不起作用

Question

当其他语句都不为true时，语句的else部分不会执行。

if (personPlay.equals(computerPlay)) 
     System.out.println("It's a tie!"); 
    else if (personPlay.equals("R")) 
     if (computerPlay.equals("S")) 
     System.out.println("Rock crushes scissors. You win!!"); 
    else if (personPlay.equals("P")) 
     if (computerPlay.equals("R")) 
     System.out.println("Paper raps around rock. You win!"); 
    else if (personPlay.equals("S")) 
     if (computerPlay.equals("P")) 
     System.out.println("Scissors cut paper. You win!"); 
    else 
     System.out.println("you lose"); 

Answer 1

使用括号：

if (personPlay.equals(computerPlay)) { 
    System.out.println("It's a tie!"); 
} else if (personPlay.equals("R")) { 
    if (computerPlay.equals("S")) 
     System.out.println("Rock crushes scissors. You win!!"); 
} else if (personPlay.equals("P")) { 
    if (computerPlay.equals("R")) 
     System.out.println("Paper wraps around rock. You win!"); 
} else if (personPlay.equals("S")) { 
    if (computerPlay.equals("P")) 
     System.out.println("Scissors cut paper. You win!"); 
} else { 
    System.out.println("you lose"); 
} 

正如评论所说，该代码仍然不能工作，因为逻辑是有缺陷的。您应该在每个内部if else子句，其中应打印“你输”：

if (personPlay.equals(computerPlay)) { 
    System.out.println("It's a tie!"); 
} else if (personPlay.equals("R")) { 
    if (computerPlay.equals("S")) 
     System.out.println("Rock crushes scissors. You win!!"); 
    else 
     System.out.println("you lose"); 
} else if (personPlay.equals("P")) { 
    if (computerPlay.equals("R")) 
     System.out.println("Paper wraps around rock. You win!"); 
    else 
     System.out.println("you lose"); 
} else if (personPlay.equals("S")) { 
    if (computerPlay.equals("P")) 
     System.out.println("Scissors cut paper. You win!"); 
    else 
     System.out.println("you lose"); 
} else { 
    System.out.println("invalid input"); 
} 

或者你也可以消除内部if S和使用&&代替：

if (personPlay.equals(computerPlay)) { 
    System.out.println("It's a tie!"); 
} else if (personPlay.equals("R") && computerPlay.equals("S")) { 
     System.out.println("Rock crushes scissors. You win!!"); 
} else if (personPlay.equals("P") && computerPlay.equals("R")) { 
     System.out.println("Paper wraps around rock. You win!"); 
} else if (personPlay.equals("S") && computerPlay.equals("P")) { 
     System.out.println("Scissors cut paper. You win!"); 
} else { 
    System.out.println("you lose"); 
}