java中Lambda表达式相关的四大内置核心函数式接口

知识点：java8中四大内置核心函数式接口

/**
 * 1. Consumer<T>:消费型接口
 *      void accept(T t);
 *
 * 2. Supplier<T> :供给型接口
 *       T  get();
 *
 * 3. Function<T,R>: 函数型接口
 *     R  apply(T t);
 *
 * 4. Predicate<T>: 断言型接口
 *    boolean test(T t)
 * **/
public class TestLambda {

    //1.Consumer<T>:消费型接口  void accept(T t);
    @Test
    public void test(){
        shopping(1000,(x)-> System.out.println("今天购物发了"+x+"元"));
    }
    public  void shopping(double money, Consumer<Double> con){
        con.accept(money);
    }
    
    //2.Supplier<T> :供给型接口  T  get();
    @Test
    public void test2(){
        List<Integer> numList=getNumList(3,()->(int)(Math.random()*10));
        for (Integer n:numList
             ) {
            System.out.println(n);
        }
    }
    //产生指定个数的整数，放到集合中并返回
    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;
    }


    //3.Function<T,R>: 函数型接口  R  apply(T t);
    @Test
    public void test3(){
      String newStr= handlerStr("helloworld",(str)->str.substring(3,6));
      System.out.println(newStr);
    }
    //处理字符串
    public String handlerStr(String str, Function<String,String> fun){
        return fun.apply(str);
    }

    //4.Predicate<T>: 断言型接口 boolean test(T t)
    @Test
    public void test4(){
        List<String> list= Arrays.asList("idea","eclipse","predicate","function");
        List<String> returnList= filterStr(list,(str)->str.length()>4);
        for (String str:returnList
             ) {
            System.out.println(str);
        }
    }
    //将满足条件的字符串，放到集合中
    public List<String> filterStr(List<String> list, Predicate<String> pre){
        List<String> newList=new ArrayList<>();
        for (String str:list
             ) {
            if(pre.test(str)){
               newList.add(str);
            }
        }
        return newList;
    }
}