JUC并发编程——四大函数式接口（基于狂神说的学习笔记）

四大函数式接口

函数式接口：只有一个方法的接口 ，例如：Runnable接口

Function

函数型接口，有一个输入参数，有一个输出

源码：

/**
 * Represents a function that accepts one argument and produces a result.
 *
 * This is a functional interface
 * whose functional method is apply(Object).
 *
 * @param  the type of the input to the function
 * @param  the type of the result of the function
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Function<T, R> {

    /**
     * Applies this function to the given argument.
     *
     * @param t the function argument
     * @return the function result
     */
    R apply(T t);

示例：

package function;

import java.util.function.Function;

/**
 *
 * Function 函数型接口，有一个输入参数，有一个输出
 * 只要是函数式接口，就可以用lambda表达式
 */
public class Demo01 {
    public static void main(String[] args) {

        // 匿名内部类，工具类，输出输入的结果
//        Function function = new Function() {
//            @Override
//            public String apply(String s) {
//
//                return null;
//            }
//        };
        // 使用lambda表达式
        Function function = (str)->{
            return str;
        };
        System.out.println(function.apply("abc"));

    }
}

Predicate

断定型接口：只有一个输入参数，返回值为boolean

源码：

/**
 * Represents a predicate (boolean-valued function) of one argument.
 *
 * This is a functional interface
 * whose functional method is test(Object).
 *
 * @param  the type of the input to the predicate
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Predicate<T> {

    /**
     * Evaluates this predicate on the given argument.
     *
     * @param t the input argument
     * @return {@code true} if the input argument matches the predicate,
     * otherwise {@code false}
     */
    boolean test(T t);

示例

package function;

import java.util.function.Predicate;

/**
 *
 * 断定型接口：有一个输入参数，返回值为boolean
 */
public class Demo02 {

    public static void main(String[] args) {

        // 判断字符串是否为空
//        Predicate predicate = new Predicate() {
//            @Override
//            public boolean test(String s) {
//                return s.isEmpty();
//            }
//        };
        // 函数型接口+lambda表达式，使代码看起来更加简洁
        Predicate<String> predicate = (s)->{return s.isEmpty();};
        System.out.println(predicate.test(""));
    }
}

Consumer

消费型接口，有一个参数，没有返回值

源码：

/**
 * Represents an operation that accepts a single input argument and returns no
 * result. Unlike most other functional interfaces, {@code Consumer} is expected
 * to operate via side-effects.
 *
 * 
This is afunctional interface
 * whose functional method is accept(Object).
 *
 * @param  the type of the input to the operation
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Consumer<T> {

    /**
     * Performs this operation on the given argument.
     *
     * @param t the input argument
     */
    void accept(T t);

示例

package function;

import javax.lang.model.element.NestingKind;
import java.util.function.Consumer;

/**
 *
 * Consumer 消费型接口：只有输入，没有返回值
 */
public class Demo03 {

    public static void main(String[] args) {
//        Consumer consumer = new Consumer() {
//            @Override
//            public void accept(String s) {
//                System.out.println(s);
//            }
//        };

        Consumer<String> consumer = (s)->{
            System.out.println(s);
        };
        consumer.accept("asd");
    }
}

Supplier

供给型接口：没有参数，只有返回值

源码：

/**
 * Represents a supplier of results.
 *
 * There is no requirement that a new or distinct result be returned each
 * time the supplier is invoked.
 *
 *  the type of results supplied by this supplier
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Supplier<T> {

    /**
     * Gets a result.
     *
     * @return a result
     */
    T get();
}

示例

package function;

import java.util.function.Supplier;

/**
 *
 * 供给型接口：没有参数，只有返回值
 */
public class Demo04 {

    public static void main(String[] args) {
//        Supplier supplier = new Supplier() {
//
//            @Override
//            public Integer get() {
//                return 1024;
//            }
//        };

        Supplier<Integer> supplier  = ()->{
            return 1024;
        };
        System.out.println(supplier.get());


    }
}

为什么要学习函数式接口？

• 简化编程模型，使代码更加可读易懂

• 在新版本的框架底层中，函数式接口有大量的应用