如何在Java中将函数作为参数传递? [英] How to pass a function as a parameter in Java?

问题描述

在Java中，如何将一个函数作为另一个函数的参数传递?

In Java, how can one pass a function as an argument of another function?

推荐答案

Java 8 及更高版本

使用 Java 8+ lambda 表达式，如果您的类或接口只有一个抽象方法(有时称为 SAM 类型)，例如:

public interface MyInterface {
    String doSomething(int param1, String param2);
}

然后在使用 MyInterface 的任何地方，您都可以替换 lambda 表达式:

then anywhere where MyInterface is used, you can substitute a lambda expression:

class MyClass {
    public MyInterface myInterface = (p1, p2) -> { return p2 + p1; };
}

例如，您可以非常快速地创建一个新线程:

For example, you can create a new thread very quickly:

new Thread(() -> someMethod()).start();

并使用方法参考语法使其均匀清洁工:

And use the method reference syntax to make it even cleaner:

new Thread(this::someMethod).start();

如果没有 lambda 表达式，最后两个示例将如下所示:

Without lambda expressions, these last two examples would look like:

new Thread(new Runnable() { someMethod(); }).start();

Java 8 之前

一个常见的模式是将它包装"在一个接口中，例如Callable，然后你传入一个Callable:

Before Java 8

A common pattern would be to 'wrap' it within an interface, like Callable, for example, then you pass in a Callable:

public T myMethod(Callable<T> func) {
    return func.call();
}

这种模式被称为命令模式.

请记住，最好为您的特定用途创建一个界面.如果您选择使用 callable，那么您可以将上面的 T 替换为您期望的任何类型的返回值，例如 String.

Keep in mind you would be best off creating an interface for your particular usage. If you chose to go with callable, then you'd replace T above with whatever type of return value you expect, such as String.

针对您在下面的评论，您可以说:

In response to your comment below you could say:

public int methodToPass() { 
        // do something
}

public void dansMethod(int i, Callable<Integer> myFunc) {
       // do something
}

然后调用它，也许使用匿名内部类:

then call it, perhaps using an anonymous inner class:

dansMethod(100, new Callable<Integer>() {
   public Integer call() {
        return methodToPass();
   }
});

请记住，这不是技巧".它只是 Java 中与函数指针等价的基本概念.

Keep in mind this is not a 'trick'. It's just java's basic conceptual equivalent to function pointers.

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