java lambda 函数是否唯一（不同的 hashCode 且不等于）？

Question

我想知道 java lambda 函数是否总是唯一的？如果是，是什么让它与众不同？

在这个伪代码中，我有两个 Consumer 和一些代码但不相等，hashCodes 也不同。

    Consumer<String> c1 = s -> {
        System.out.println(s);
    };
    Consumer<String> c2 = s -> {
        System.out.println(s);
    };

    System.out.println(c1.hashCode());  
    System.out.println(c2.hashCode());
    System.out.println(c1.equals(c2)); // false:  is it always false?

我想在一个 Set 中存储一个 lambda 列表，我不确定如果我不小心得到了两个具有相同 hashCode 的 lambda 函数，我是否会丢失一些元素。

Answer 1

根据JLS 15.27.4（强调我的）：

The value of a lambda expression is a reference to an instance of a class with the following properties:

[...]

The class overrides no other methods of the targeted functional interface type or other interface types mentioned above, although it may override methods of the Object class.

因为它说“可以”，所以 lambda 的 class 可能有 equals 和 hashCode 的自定义实现，也可能没有，具体取决于实现。

另请注意：

These rules are meant to offer flexibility to implementations of the Java programming language, in that:

A new object need not be allocated on every evaluation.

Objects produced by different lambda expressions need not belong to different classes (if the bodies are identical, for example).

Every object produced by evaluation need not belong to the same class (captured local variables might be inlined, for example).

If an "existing instance" is available, it need not have been created at a previous lambda evaluation (it might have been allocated during the enclosing class's initialization, for example).

一个实现可能会看到您的两个 lambda 具有相同的主体，并且只为您的 lambda 生成一个 class。 class 的 equals 方法可以被重写为 return true，对于任何也是 class 实例的对象。它甚至可以为您的两个 lambda 使用相同的对象！在任何一种情况下，如果您将两个 lambda 都添加到您的集合中，您的集合将只有一个元素。

java lambda 函数是否唯一（不同的 hashCode 且不等于）？

Are java lambda functions unique (different hashCode and not equals)?

java

lambda

java-11