jdk新特性（二）stream流

素颜马尾好姑娘i 2022-12-13 01:38 307阅读 0赞

## stream流 ##

为什么需要stream流，  
1、Stream流的引入可以使编程更加优雅，去除冗余代码，增加代码运行效率。  
2、Stream流把真正的函数式编程风格引入到Java中。

### 案例 ###

public class Actor {
        private String name;
        private String sex;
        private int age;
    
        public Actor() {
        }
    
        public Actor(String name, String sex, int age) {
            this.name = name;
            this.sex = sex;
            this.age = age;
        }
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public String getSex() {
            return sex;
        }
    
        public void setSex(String sex) {
            this.sex = sex;
        }
    
        public int getAge() {
            return age;
        }
    
        public void setAge(int age) {
            this.age = age;
        }
    
    
        public void setFeatures(String name, String sex, int age){
            this.name = name;
            this.sex = sex;
            this.age = age;
        }
    
        @Override
        public String toString() {
            return "StreamTest{" +
                    "name='" + name + '\'' +
                    ", sex='" + sex + '\'' +
                    ", age=" + age +
                    '}';
        }
    }

测试类

public class StreamTest {
        public static void main(String[] args) {
            ArrayList<Actor> actors = new ArrayList<>();
            Actor[] act = new Actor[12];
            for (int i = 0; i < act.length; i++) {
                act[i]=new Actor();
            }
            act[0].setFeatures("赵丽颖","女",34);
            act[1].setFeatures("杨颖","女",39);
            act[2].setFeatures("李易峰","男",36);
            act[3].setFeatures("郭德纲","男",61);
            act[4].setFeatures("杨幂","女",38);
            act[5].setFeatures("李沁","女",35);
            act[6].setFeatures("张子健","男",47);
            act[7].setFeatures("何家劲","男",52);
            act[8].setFeatures("金超群","男",56);
            act[9].setFeatures("萨顶顶","女",44);
            act[10].setFeatures("杨紫","女",28);
            act[11].setFeatures("陈乔恩","女",39);
    
            System.out.println("--------------处理前--------------");
            for (Actor actor : act) {
                actors.add(actor);
                System.out.println(actor);
            }
    
            System.out.println("---------------处理后----------");
            Stream<Actor> womanStream = actors.stream()
                    .filter((s) -> "女".equals(s.getSex()))
                    .filter(s -> s.getName().startsWith("杨"))
                    .filter(s -> s.getAge() > 35);
    
            Stream<Actor> manStream = actors.stream().filter((s) -> s.getName().length() > 2)
                    .filter(s->"男".equals(s.getSex()))
                    .filter(s->s.getAge()>35)
                    .skip(1)
                    .limit(3);
    
            Stream<Actor> concat = Stream.concat(manStream, womanStream);
            System.out.println("-----------------------------");
            //用集合来收集
            Map<String, Integer> collect = concat.collect(Collectors.toMap(s -> s.getName(), s -> s.getAge()));
            Set<Map.Entry<String, Integer>> entries = collect.entrySet();
            for (Map.Entry<String, Integer> entry :
                    entries) {
                System.out.println(entry.getKey()+":"+entry.getValue());
            }
            /*System.out.println("-----------------------");
            Set<String> strings = collect.keySet();
            for (String string : strings) {
                System.out.println(string+":"+collect.get(string));
            }*/
            //List<Actor> collect = concat.collect(Collectors.toList());
            //System.out.println(collect);
            // concat.map(Actor::getName).forEach(System.out::println);
        }
    }

测试结果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1ZXNoYW5mZWl0aWFu_size_16_color_FFFFFF_t_70_pic_center]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3h1ZXNoYW5mZWl0aWFu_size_16_color_FFFFFF_t_70_pic_center]: /images/20221123/ae4b3d5ebda548098fdb8924fac161bb.png