java - Java While Loops Issue

Question

I am using a while loop and an if loop to determine a response and action. For some odd reason it continues to ignore my if statements.

            Boolean _exit = false;
        while (_exit == false){
            System.out.println("\nWould you like another meal?\tYes or No?");
            String answer = scan.next().toLowerCase();
            if (answer == "yes"){
                System.out.println("Reached1");
                _exit = true;
            }
            if (answer == "no"){
                System.out.println("Reached1");
                exit = _exit = true;
            }

Could someone explain what is happening and why it is failing to check the if statements. I've tried scan.nextLine as well. This problem even persisted when I removed of the toLowerCase as it was brought to my attention that it can have an affect on string values, though I did try Locale.English.

Any suggestions?

Answer 1

Compare Strings with .equals() not == in your if statements:

if (answer.equals("yes")){
            System.out.println("Reached1");
            _exit = true;
        }
        if (answer.equals("no")){
            System.out.println("Reached1");
            exit = _exit = true;
        }

Answer 2

从另一个线程：

==测试参考相等。

.equals()测试值相等。

因此，如果您真的想测试两个字符串是否具有相同的值，您应该使用.equals()（除了在少数情况下，您可以保证具有相同值的两个字符串将由相同的对象表示，例如：String interning）。

==用于测试两个字符串是否是同一个对象。

// These two have the same value
new String("test").equals("test") ==> true 

// ... but they are not the same object
new String("test") == "test" ==> false 

// ... neither are these
new String("test") == new String("test") ==> false 

// ... but these are because literals are interned by 
// the compiler and thus refer to the same object
"test" == "test" ==> true 

// concatenation of string literals happens at compile time resulting in same objects
"test" == "te" + "st"  ==> true

// but .substring() is invoked at runtime, generating distinct objects
"test" == "!test".substring(1) ==> false

重要的是要注意它==比equals()（单个指针比较而不是循环）便宜得多，因此，在它适用的情况下（即您可以保证您只处理内部字符串）它可以带来重要的性能改进. 但是，这些情况很少见。

资料来源：如何比较 Java 中的字符串？