JAVA四大内置函数

/**
 * Consumer<T> : 消费型接口
 * void accept(T t);
 *
 * Supplier<T> : 供给型接口
 * T get();
 *
 * Function<T, R> : 函数型接口
 * R apply(T t);
 *
 * Predicate<T> : 断言型接口
 * boolean test(T t);
 *
 *
 */

    @Test
    public void test1() {
        happy(10000,x -> System.out.println("喜欢大保健,每次消费"+ x));
        happy(10000,x -> {
            double a = x*100;
        });
    }

    public void happy(double money, Consumer<Double> con) {
        con.accept(money);
    }

test1结果：

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//Supplier<T> 供给型接口：
    @Test
    public void test2(){
        List<Integer> numList = getNumList(10,() -> (int)(Math.random()*100));
        for(Integer num : numList) {
            System.out.println(num);
        }
    }

    //需求：产生指定个数的整数，并放入集合中
    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;
    }

 test2结果：

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//Function<T, R> 函数式接口
    @Test
    public void test3() {
        Integer num = strHandler("123",(x) -> Integer.valueOf(x) +10000);
        System.out.println(num);
    }

    //用于处理字符串
    public Integer strHandler(String str, Function<String,Integer> fun) {
        return fun.apply(str);
    }

 test3结果：

---

//Predicate<T> 断言型接口
    @Test
    public void test4() {
        List<String> list = Arrays.asList("helloww","www","abcdefg","ss","youyiku");
        List<String> strings = filterStr(list, (x) -> x.length() > 3);
        for(String s: strings) {
            System.out.println(s);
        }

    }

    //需求，将满足条件的字符串，放入集合中
    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 4结果：