Java 要比较 UUID，我可以使用 == 还是必须使用 UUID.equals(UUID)？
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To compare UUID, can I use == or have to use UUID.equals(UUID)?
提问by Newyacht Zhang
Just start using java.util.UUID. My question is if I have two UUID variables, say u1 and u2, and I would like to check if they are equal, can I safely use expression u1 == u2or have to write u1.equals(u2)? assuming both are not null.
刚开始使用java.util.UUID。我的问题是，如果我有两个 UUID 变量，比如 u1 和 u2，我想检查它们是否相等，我可以安全地使用表达式u1 == u2还是必须写u1.equals(u2)？假设两者都不为空。
BTW, I am using its randomUUIDmethod to create new UUID values, but I think this should not be matter.
I wonder as UUID is unique, each value could be a singleton, then it is safe to use u1 == u2.
顺便说一句，我正在使用它的randomUUID方法来创建新的 UUID 值，但我认为这应该无关紧要。我想知道 UUID 是唯一的，每个值都可以是一个单例，那么使用u1 == u2.
void method1(UUID u1, UUID u2) {
// I know it is always safe to use equal method
if (u1.equals(u2)){
// do something
}
// is it safe to use ==
if (u1 == u2) {
// do something
}
}
采纳答案by user253751
It depends: which type of equality do you want?
这取决于：您想要哪种类型的平等？
UUID a = new UUID(12345678, 87654321);
UUID b = new UUID(12345678, 87654321);
UUID c = new UUID(11111111, 22222222);
System.out.println(a == a); // returns true
System.out.println(a.equals(a)); // returns true
System.out.println(a == b); // returns false
System.out.println(a.equals(b)); // returns true
System.out.println(a == c); // returns false
System.out.println(a.equals(c)); // returns false
a == bis true only if aand bare the same object. If they are two identical objects, it will still be false.
a == b仅当a和b是同一个对象时才为真。如果它们是两个相同的对象，它仍然是假的。
a.equals(b)is true if aand bare the same UUID value - if their two parts are the same.
a.equals(b)如果a和b是相同的 UUID 值 - 如果它们的两个部分相同，则为真。
回答by Makoto
Well...no.
嗯……不。
==against an object checks for reference equality. That is, it checks to see if these two objects are literally the same spot in memory.
==针对对象检查引用相等性。也就是说，它会检查这两个对象是否在内存中实际上是同一个位置。
.equals()will check for actual object equivalence. And, the Javadoc for UUIDgoes into great detail to explain when two UUIDinstances are equivalent.
.equals()将检查实际的对象等效性。并且，Javadoc forUUID非常详细地解释了何时两个UUID实例是等效的。
