java8特性之函数式接口

Z时代
2024-01-10
分类：综合

java.util.function中 Function, Supplier, Consumer, Predicate和其他函数式接口广泛用在支持lambda表达式的API中。这些接口有一个抽象方法，会被lambda表达式的定义所覆盖。注解都是@FunctionalInterface

Consumer消费


  List<Person> lisiList = new ArrayList<>();
        Consumer <Person> consumer  =  x -> {
            if (x.name.equals("lisi")){
                lisiList.add(x);
            }
        };
        Stream.of(
                new Person(21,"zhangsan"),
                new Person(22,"lisi"),
                new Person(23,"wangwu"),
                new Person(24,"wangwu"),
                new Person(23,"lisi"),
                new Person(26,"lisi"),
                new Person(26,"zhangsan")
        ).forEach(consumer);
        System.out.println(JSON.toJSONString(lisiList));
// 结果[{"age":22,"name":"lisi"},{"age":23,"name":"lisi"},{"age":26,"name":"lisi"}]
 List<Person> lisiList = new ArrayList<>();
        Consumer <Person> consumer  =  x -> {
            if (x.name.equals("lisi")){
                lisiList.add(x);
            }
        };
        consumer = consumer.andThen(
           x -> lisiList.removeIf(y -> y.age < 23)
        );
        Stream.of(
                new Person(21,"zhangsan"),
                new Person(22,"lisi"),
                new Person(23,"wangwu"),
                new Person(24,"wangwu"),
                new Person(23,"lisi"),
                new Person(26,"lisi"),
                new Person(26,"zhangsan")
        ).forEach(consumer);
        System.out.println(JSON.toJSONString(lisiList));
// 结果 [{"age":23,"name":"lisi"},{"age":26,"name":"lisi"}]

Supplier供给


     public List<Integer> getNumList(int num, Supplier<Integer> sup){
      List<Integer> list = new ArrayList<>();
      for(int i=0;i<num;i++){
          Integer a = sup.get();
          list.add(a);
      }
      return list;
    }
    @Test
    public void test2(){
        List<Integer> list = getNumList(5,() -> (int)(Math.random()*100));
        for(Integer i:list){
            System.out.println(i);
        }
    }

Function函数


    public String strHander(String str, Function<String,String> fun){
        return fun.apply(str.toLowerCase());
    } 
    @Test
    public void test3(){
       String str = strHander("Hello world",(t) -> t.replace("o","a"));
        System.out.println(str);
    }

Predicate策略


     public List<String> filterStr(List<String> strs, Predicate<String> pre){
        List<String> list = new ArrayList<>();
        for(String str:strs){
            if(pre.test(str)){
                list.add(str);
            }
        }
        return list;
    }
    @Test
    public void test4(){
        List<String> list = Arrays.asList("abc","dedff","dde","ccdee","fde");
        list = filterStr(list,(x)->x.length()==3);
        for(String str:list){
            System.out.println(str);
        }
    }