java8之方法锦集

一、遍历map集合的4种方式

    public static void show(Map<String,Integer> map){
        //第一种：获取map键值
        for(String in : map.keySet()){
            Integer z = map.get(in);
            System.out.println(in+"=="+z);
        }

        //第二种：获取map键值【推荐使用这种】
        for(Map.Entry<String,Integer> m : map.entrySet()){
            System.out.println(m.getKey()+"=="+m.getValue());
        }

        //第三种：获取map值
        for(Integer i : map.values()){
            System.out.println(i+"==");
        }
        
        //第四种：获取map键值 
Iterator<Map.Entry<Integer, String>> it1 = map.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<Integer, String> entry = it1.next();
            System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
        }
        //【拓展】
        Iterator<Employee> it = es.iterator();
        while (it.hasNext()){
            System.out.println(it.next());
        }
    }

二、比较大小

    public void test2(){
        Collections.sort(es,(q1,q2)->{
            if(q1.getAge()==q2.getAge()){
                return q2.getName().compareTo(q1.getName());//小.compareTo(大)；
            }else {
                return Integer.compare(q1.getAge(),q2.getAge());
            }
        });
        es.forEach(System.out::println);
    }

三、四大核心函数式接口

    @Test
    public void test2(){
        System.out.println(filter("\t\t\t你好",(s)->s.length()>2));
        
        System.out.println(show("asdf",(z)->z.toUpperCase()));
        
        System.out.println(getNum(5,()->(int)(Math.random()*100)));
        
        consume(125,(z)-> System.out.println(z));
    }
    public static List<Integer> getNum(Integer num, Supplier<Integer> s){
        List<Integer> ls = new ArrayList<>();
        for (Integer i = 0; i < num; i++) {
            ls.add(s.get());
        }
        return ls;
    }
    public static String show(String s , Function<String,String> m){
        return m.apply(s);
    }
    public static void consume(Integer s , Consumer<Integer> m){
        m.accept(s);
    }
    public static List<String> filter(String s, Predicate<String> p){

        List<String> ls = new ArrayList<>();
        if(p.test(s)){
            ls.add(s);
        }

        return ls;
    }

四、方法引用

    @Test
    public void test1(){
        Consumer<String> z=  System.out::println;
        z.accept("zzzz");

        Employee e=  new Employee(1,"2",212);
        Supplier<String> s = ()->e.getName();
        System.out.println(s.get());

        Supplier<Integer> z0 = e::getAge;
        System.out.println(z0.get());

        Comparator<Integer> con = Integer::compare;
        System.out.println(con.compare(1,2));

//        lamda体的参数列表和返回值类型，与函数式接口中的返回值，保持一致。

        Supplier<Employee> s1 = ()->new Employee(1,"1",1);
        System.out.println(s1.get());

        Supplier<Employee> z1 = Employee::new;
        System.out.println(z1.get());

        Function<Integer,Employee> c=  Employee::new;
        Employee x= c.apply(1);
        System.out.println(x);

        BiFunction<Integer,String,Employee> b = Employee::new;
        Employee a = b.apply(1,"1");
        System.out.println(a);

        Function<Integer,String[]> f = String[]::new;
        String[] a1 = f.apply(20);
        System.out.println(a1.length);
    }