一、前言

在上一篇文章中已经完成了Lambda表达式语法和使用。
lambda表达式高级应用

二、lambda表达式高级使用

• 静态方法的使用
• 实例方法的使用
• 抽象方法的使用,绑定函数式接口

public class Test {
    /**
     * 1.静态方法引用
     * 类型名称：：方法名称
     */
    public static void main(String[] args) {
        List<Person> peopleList = new ArrayList<>();
        peopleList.add(new Person("tom","男",15));
        peopleList.add(new Person("jarry","女",16));
        peopleList.add(new Person("mina","男",32));
        peopleList.add(new Person("lilei","女",26));
        peopleList.add(new Person("hanmeimei","男",32));

        //1.匿名内部类
        Collections.sort(peopleList, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                return o1.getAge() - o2.getAge();
            }
        });
        //System.out.println(peopleList);

        //2.lamda表达式
        Collections.sort(peopleList,(p1,p2)->p1.getAge()-p2.getAge());
        //System.out.println(peopleList);

        //3.静态方发的引用
        Collections.sort(peopleList,Person::compareByAge);
        //System.out.println(peopleList);

        //4.实例方法的使用
        PersonUtil personUtil = new PersonUtil();
        Collections.sort(peopleList,personUtil::compareByName);
        System.out.println(peopleList);

        //5.抽象方法的使用,绑定函数式接口
        Iperson iperson = Person::new;
        Person person = iperson.initPerson("hm", "nan", 13);
        System.out.println(person);

    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
class Person{
    private String name;
    private String gender;
    private int age;

    public static int compareByAge(Person p1,Person p2){
        return p1.getAge() - p2.getAge();
    }
}

class PersonUtil{
    //实例方法
    public int compareByName(Person p1,Person p2){
        return p1.getName().hashCode() - p2.getName().hashCode();
    }
}

interface Iperson{
    Person initPerson(String name,String gender,int age);
}

三 Stream操作List对象demo

我们以前操作list对象多使用for或者迭代器模式，现在加上java8 stream处理

public class Test {
    public static void main(String[] args) {
        //1. 数据
        List<String> accounts = new ArrayList<>();
        accounts.add("tom");
        accounts.add("jerry");
        accounts.add("beita");
        accounts.add("shuke");
        accounts.add("damu");

        //1.1 业务要求：长度大于等于5的为有效账号
        for(String account : accounts){
            if(account.length()>=5){
                System.out.println("有效账号为： " + account);
            }
        }
        //1.2 迭代器方式
        Iterator<String> iterator = accounts.iterator();
        while (iterator.hasNext()){
            if(iterator.next().length()>=5){
                System.out.println("it 有效账号为： " + iterator.next());
            }
        }
        //1.3 stream结合lambda表达式
        List<String> list = accounts.stream().filter(s -> s.length() >= 5).collect(Collectors.toList());
        System.out.println(list.toString());
    }
}

四 stream API使用

4.1 各种对象转成stream对象

stream使用第一步就是把list,array,set,map等对象转成stream对象

//1. 批量数据 -> stream对象
        //多个数据
        Stream<String> stream = Stream.of("1", "2", "3");
        //数组
        String [] array = new String[]{"xueqi","biyao"};
        Stream stream2 = Arrays.stream(array);

        //列表
        List<String> list = new ArrayList<>();
        list.add("1");
        list.add("2");
        list.add("3");
        list.add("4");
        Stream<String> stream3 = list.stream();

        //集合
        Set<String> set = new HashSet<>();
        set.add("1");
        set.add("2");
        set.add("3");
        Stream<String> stream1 = set.stream();

        //map
        Map<String,Integer> map =  new HashMap<>();
        map.put("tom",1000);
        map.put("jerry",1200);
        map.put("lilie",1000);
        Stream<Map.Entry<String, Integer>> stream4 = map.entrySet().stream();

        //stream对象对基本类型数据功能封装
        IntStream.of(new int[]{10,20,30}).forEach(System.out::println);
        IntStream.range(1,5).forEach(System.out::println);
        IntStream.rangeClosed(1,5).forEach(System.out::println);

4.2 stream对象转操作类型