java – 如何为Runnable分配方法引用值

发布时间：2020-12-14 05:30:17 所属栏目：Java 来源：网络整理

导读：我讨论了 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(St

我讨论了 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;
}

正如代码所示,我理解r1是正确的,r3是错误的,但我不明白为什么r2也是对的.有人可以帮我理解吗

解决方法

由于 section 15.13.2 of the JLS,r2是罚款,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.

基本上写t2()有效;并且只是忽略返回值,因此创建一个调用该方法并忽略返回值的方法引用是有效的.

t3是无效的,因为你必须提供一个参数,而Runnable没有参数,所以没有什么可以“传递”给方法.

（编辑：李大同）

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