Java做while循环使字符串测试行为不同 [英] Java do while loop making string testing act differently

问题描述

我对使用||的行为感到非常困惑.equals函数的运算符。有没有理由我不能在字符串或其他东西上使用它？

I am very confused at the behavior of using the || operator on the .equals function. Is there a reason I can not use it on strings or something?

这是有效的：

do{
  System.out.println("Play again? [Y/N]");
  //input: Y      
  play = in.nextLine();
  play = play.toUpperCase();

}
while(!"Y".equals(input) ); //breaks out of loop (as it should)

为什么这不起作用？！

do{
  System.out.println("Play again? [Y/N]");
  //input: Y      
  play = in.nextLine();
  play = play.toUpperCase();

}
while( !"Y".equals(input) || !"N".equals(input) ); //infinite loop

推荐答案

让我们把它说成文字。

吃掉所有这些水果，只要它不是苹果或它不是橙子。

"Eat all of this fruit as long as it's not an apple OR it's not an orange."

• 草莓：不是苹果，继续。


• 香蕉：不是苹果，继续。


• 橙色：不是苹果，所以......继续。


• Apple：是苹果;但实际上不是橙色，所以...继续...... :(

• Strawberry: not an apple, continue.
• Banana: not an apple, continue.
• Orange: not an apple, so... continue.
• Apple: is apple; but is actually not an orange, so... continue...... :(

如果它是苹果，不是一个橙色将是真的;如果它是一个橙色，不是一个苹果将是真的;如果它是一个奇异果，两者都将是真的。没有办法停止进食（除非你爆炸或陷入昏迷）。

If it's an apple, "not an orange" will be true; if it's an orange, "not an apple" will be true; if it's a kiwi, both will be true. There is no way to stop eating (unless you explode or crash into a coma).

错误的逻辑会导致人们死于水果。

Bad logic leads people to death by fruit.

你想要吃掉所有这些水果，只要它是不是苹果，也不是橙子。

You want "eat all of this fruit as long as it's not an apple AND ALSO not an orange".

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