问题描述
根据 Groovy 文档，== 只是一个聪明的"equals() 因为它还负责避免 NullPointerException:
According to the Groovy docs, the == is just a "clever" equals() as it also takes care of avoiding NullPointerException:
Java的==其实就是Groovy的is()方法，而Groovy的==是一个巧妙的equals()代码>!
[...]
但是要进行通常的 equals() 比较，您应该更喜欢 Groovy 的 ==，因为它还可以避免 NullPointerException，与左侧或右侧是否 null 无关.
But to do the usual equals() comparison, you should prefer Groovy’s ==, as it also takes care of avoiding NullPointerException, independently of whether the left or right is null or not.
因此，如果对象不为空，== 和 equals() 应该返回相同的值.但是，我在执行以下脚本时得到了意想不到的结果:
So, the == and equals() should return the same value if the objects are not null. However, I'm getting unexpected results on executing the following script:
println "${'test'}" == 'test'
println "${'test'}".equals('test')
我得到的输出是:
true
false
这是一个与 GStringImpl 相关的已知错误还是我遗漏的东西?
Is this a known bug related to GStringImpl or something that I'm missing?
推荐答案
好问题，上面代码令人惊讶的地方是
Nice question, the surprising thing about the code above is that
println "${'test'}".equals('test')
返回 false.另一行代码返回预期结果，所以让我们忘记这一点.
returns false. The other line of code returns the expected result, so let's forget about that.
"${'test'}".equals('test')
equals 被调用的对象是 GStringImpl 类型，而 'test' 是 String 类型，因此它们不被视为相等.
The object that equals is called on is of type GStringImpl whereas 'test' is of type String, so they are not considered equal.
显然，equals 的 GStringImpl 实现可以这样编写，这样当它传递一个 String 时，它包含与 this，它返回真.表面上看，这似乎是一个合理的做法.
Obviously the GStringImpl implementation of equals could have been written such that when it is passed a String that contain the same characters as this, it returns true. Prima facie, this seems like a reasonable thing to do.
我猜它不是这样写的原因是因为它违反了 equals 约定，其中规定:
I'm guessing that the reason it wasn't written this way is because it would violate the equals contract, which states that:
它是对称的:对于任何非空引用值 x 和 y，当且仅当 y.equals(x) 返回 true 时，x.equals(y) 才应返回 true.
String.equals(Object other)的实现在传递一个GSStringImpl时总是会返回false，所以如果GStringImpl.equals(Object other)code>在传递任何String时返回true，这将违反对称要求.
The implementation of String.equals(Object other) will always return false when passed a GSStringImpl, so if GStringImpl.equals(Object other) returns true when passed any String, it would be in violation of the symmetric requirement.
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