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");
}

正如评论中提到的，这段代码仍然无法工作，因为逻辑有缺陷。您应该在每个内部 if 中有一个 else 子句，其中您应该打印“youlos”:

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");
}

或者您可以消除内部 if 并使用 && 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");
}