java8：四大函数式接口（Consumer、Supplier、Function、Predicate）

1、 消费型接口：Consumer

（1）函数式接口

@FunctionalInterface
public interface Consumer<T> {

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

测试类

   public void happy(String string, Consumer<String> con) {
        con.accept(string);
    }

    @Test
    public void test1() {
        happy("zhai", (m) -> System.out.println("你好" + m ));
    }

你好zhai

消费型接口特点：有输入但是无返回值

2、供给型接口：Supplier

（1）函数式接口

@FunctionalInterface
public interface Supplier<T> {

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

（2）测试

 public List<Integer> getNumList(int num, Supplier<Integer> sup) {
        List<Integer> list = new ArrayList<>();

        for (int i = 0; i < num; i++) {
            Integer n = sup.get();
            list.add(n);
        }

        return list;
    }

    @Test
    public void test2() {
        List<Integer> numList = getNumList(10, () -> (int) (Math.random() * 100));

        for (Integer num : numList) {
            System.out.println(num);
        }
    }

75
1
61
85
97
25
94
41
24
90

无输入参数，有输出

3、函数型接口：Function

（1）函数式接口

@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);

（2）测试

    public String strHandler(String str, Function<String, String> fun){
        return fun.apply(str);
    }

    @Test
    public void test(){
        String newStr = strHandler("   你好   ", (str) -> str.trim());
        System.out.println(newStr);
        
        String subStr = strHandler("hello", (str) -> str.substring(2, 5));
        System.out.println(subStr);
    }

有输入参数，有返回值

4、断言型接口：Predicate

（1）函数式接口

@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);

（2）测试

   public List<String> filterStr(List<String> list, Predicate<String> pre) {
        List<String> strList = new ArrayList<>();

        for (String str : list) {
            if (pre.test(str)) {
                strList.add(str);
            }
        }

        return strList;
    }

    @Test
    public void test4() {
        List<String> list = Arrays.asList("Hello", "nihaoyyyy", "Lambda", "www", "ok");
        List<String> strList = filterStr(list, (s) -> s.length() > 3);

        for (String str : strList) {
            System.out.println(str);
        }
    }

有输入，返回值是Boolean类型的

5、其他接口

（1）其他接口