Java Functional Interface

请看如下的 Java 代码：

class MyClass {
public setCalback(Runnable doneCallback) {
		if (something is done) {
			doneCallback();
		}
	}
};
MyClass mc = new MyClass();
mc.setCallback(() -> {
	// do other things
})

为什么 lambda 可以实现Runnable 接口？

Runnable 的代码如下， 可以看到他是一个函数式接口 FunctionalInterface，类似的函数是接口，在 Java中还有很多，比如 ActionLisener 和 Comparator

package java.lang;

@FunctionalInterface
public interface Runnable {
    void run();
}

什么是函数是接口？

函数式接口是一种只有一种方法的接口。具有相同签名的 lambda 函数可以转化为这种接口。

A functional interface is an interface that contains only one abstract method. They can have only one functionality to exhibit. From Java 8 onwards, lambda expressions can be used to represent the instance of a functional interface. A functional interface can have any number of default methods. Runnable, ActionListener, Comparable are some of the examples of functional interfaces.