JAVA8新特性---函数式接口

Posted 2021-02-19 keepsummer

一、什么是函数式接口？

1. 只包含一个抽象方法的接口，称为函数式接口

2. 可以使用@Functionallinterface注解，这样可以检验它是否是一个函数式接口。同时javadoc 也会包含一条声明

3. 在java.util.function包下定义了java8的丰富的函数式接口

　　 

二、函数式接口举例

1、函数式接口

@FunctionalInterface
public interface Runnable {
    /**
     * When an object implementing interface <code>Runnable</code> is used
     * to create a thread, starting the thread causes the object\'s
     * <code>run</code> method to be called in that separately executing
     * thread.
     * <p>
     * The general contract of the method <code>run</code> is that it may
     * take any action whatsoever.
     *
     * @see     java.lang.Thread#run()
     */
    public abstract void run();
}

@FunctionalInterface
public interface Comparator<T> {
    /**
     *
     * @param o1 the first object to be compared.
     * @param o2 the second object to be compared.
     * @return a negative integer, zero, or a positive integer as the
     *         first argument is less than, equal to, or greater than the
     *         second.
     * @throws NullPointerException if an argument is null and this
     *         comparator does not permit null arguments
     * @throws ClassCastException if the arguments\' types prevent them from
     *         being compared by this comparator.
     */
    int compare(T o1, T o2);

2、自定义函数式接口

@FunctionalInterface
public interface MyNumber<T> {

public boolean compare(Integer a,Integer b);   
}

@Test
public void test2(){

   MyNumber<Integer> myNumber = (Integer a,Integer b) -> a>b;

   System.out.println(myNumber.compare(1,2));
}

三、JAVA内置的四大核心函数式接口

 

 　1、例子1

@Test
    public void test() {
        System.out.println(studytime(()->"studyTime"));

    }
    //供给型函数，无参有返回值
    public String studytime(Supplier<String> supplier){
       return supplier.get();
    }

2、例子2

 @Test
    public void test2(){
        String goodOneDay = goodDay("goodOneDay", (s -> s));
        System.out.println(goodOneDay);

    }
    public String goodDay(String s, Function<String,String> function){

        return function.apply(s);
    }

3、例子3

@Test
    public void test3(){
        List<String> list = Arrays.asList("杏鲍菇","金针菇","大枣","平菇");
        List<String> filterList = new ArrayList<>();
        list.forEach((s)-> {
           if(s.contains("菇")) {
               filterList.add(s);
           }
        });
        System.out.println("filterList:"+filterList);

    }

四、其他接口