两个字符串应该相等？ [英] Both strings should be equal?

问题描述

String s1 = "learn";
String s1 = s1+"Java";

现在s1指向learnJava字符串对吗？

now s1 is pointing to "learnJava" string right ?

String s2 = "learnJava";

if（s1 == s2）是假。为什么？

s2 应指向相同的learnJava因为它已经存在于StringConstantPool（s1）中。

s2 should point to same "learnJava" as its already present in StringConstantPool(s1).

推荐答案

s2应指向相同的learnJava 因为它已经存在于StringConstantPool中。

s2 should point to same "learnJava" as its already present in StringConstantPool.

Nope - 字符串池仅用于常量字符串，除非你打电话给实习生。

Nope - the string pool is only used for constant strings unless you call intern.

所以字符串池包含learn，Java和learnJava ...但是 s1 引用字符串池中的字符串而不是，因为连接是在执行时执行的。

So the string pool contains "learn", "Java" and "learnJava"... but s1 refers to a string not in the string pool, because the concatenation is performed at execution time.

如果你有编译时常量表达式，它会有所不同：

If you had a compile-time constant expression, it would be different:

String s1 = "learn" + "Java"; // Constant expression
String s2 = "learnJava";
System.out.println(s1 == s2); // true, guaranteed

或者如果你想保持执行时间连接：

Or if you want to keep your execution-time concatenation:

String s1 = "learn";
s1 += "Java";
s1 = s1.intern();
String s2 = "learnJava";
System.out.println(s1 == s2); // true

一般来说，只是不要将字符串与 =进行比较= = ......这几乎总是一个坏主意。

In general though, just don't compare strings with ==... it's almost always a bad idea.

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