stream结合lambda使用demo

Stream流

Java 8 API添加了一个新的抽象称为流Stream，可以让你以一种声明的方式处理数据。
Stream 使用一种类似用 SQL 语句从数据库查询数据的直观方式来提供一种对 Java 集合运算和表达的高阶抽象。
==只能用于Collection的集合==

使用的几个场景

Person类

public class Person {
    int age;
    String name;

    public Person(int age, String name) {
        this.age = age;
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "age=" + age +
                ", name='" + name + '\'' +
                '}';
    }
}

对list去重

 List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 6);
    Stream stream = list.stream().distinct();
    stream.forEach(p -> System.out.println(p));

去重并替代元素map(把person替换为里面的名字)

List<Person> list = new ArrayList<>();
        list.add(new Person(1, "A"));
        list.add(new Person(2, "B"));
        list.add(new Person(3, "C"));
        list.add(new Person(4, "D"));
        list.add(new Person(5, "E"));
        list.add(new Person(5, "E"));
        list.stream().
                distinct()
                .map(p -> p.getName())
                .forEach(c -> System.out.println("名字为：" + c));

filter过滤元素

 List<Person> list = new ArrayList<>();
        list.add(new Person(1, "A"));
        list.add(new Person(2, "B"));
        list.add(new Person(3, "C"));
        list.add(new Person(4, "D"));
        list.add(new Person(5, "E"));
        list.add(new Person(5, "E"));
        //Function<? super T, ? extends R> function = ;
        list.stream()
                .filter(person -> person.getAge() >= 3)
                .distinct()
                .map(person -> person.getName()).forEach(name -> System.out.println(name));

取集合前面三个值，用name代替person，并且排序

 List<Person> list = new ArrayList<>();
        list.add(new Person(1, "A"));
        list.add(new Person(2, "B"));
        list.add(new Person(3, "C"));
        list.add(new Person(4, "D"));
        list.add(new Person(5, "E"));
        list.add(new Person(5, "E"));
        //Function<? super T, ? extends R> function = ;
        list.stream()
                .filter(person -> person.getAge() >= 3)
                .distinct()
                .limit(3)
                .map(person -> person.getName())
                .sorted()
                .forEach(name -> System.out.println(name));