如何将方法引用值分配给 Runnable

Question

我有一个关于 Java 8 Runnable 的问题。

 public static void main(String[] args) {
    Runnable r1 = Test::t1;
    Runnable r2 = Test::t2;
    Runnable r3 = Test::t3;
}

public static void t1() {

}

public static String t2() {
    return "abc";
}

public static String t3(String t) {
    return t;
}

如代码所示，我明白r1是对的，r3是错的，但我不明白为什么r2也是对的。谁能帮我理解一下？

Answer 1

r2 可以，因为 section 15.13.2 of the JLS，其中包括：

A method reference expression is congruent with a function type if both of the following are true:

The function type identifies a single compile-time declaration corresponding to the reference.

One of the following is true:

The result of the function type is void.

The result of the function type is R, and the result of applying capture conversion (§5.1.10) to the return type of the invocation type (§15.12.2.6) of the chosen compile-time declaration is R' (where R is the target type that may be used to infer R'), and neither R nor R' is void, and R' is compatible with R in an assignment context.

基本上，编写 t2(); 并忽略 return 值是有效的，因此创建调用该方法并忽略 return 值的方法引用是有效的.

t3 不有效，因为你必须提供一个参数，而Runnable 不[=24] =] 接受一个参数，所以没有什么可以“传递”给方法。

如何将方法引用值分配给 Runnable

How assign a method reference value to Runnable

java

runnable