Java Stream流API

Java Stream流API package com.zuke.zukeliving.commodity; import java.util.Arrays; import java.util.List; import java.util.stream.Collectors; public class LearnStreamAPI { public static void main(String[] args) { // 创建Person实例 Person person1 = new Person(1, "a", 22); Person person2 = new Person(2, "b", 34); Person person3 = new Person(3, "c", 10); Person person4 = new Person(4, "d", 110); Person person5 = new Person(5, "e", 9); // 放入到list集合 List<Person> list = Arrays.asList(person1, person2, person3, person4, person5); //System.out.println(list); //分割线条，测试上面代码时请注释下面这段代码 // 需求：从list中过滤出person.id % 2 != 0 的对象 // 1. 把list转成流对象，目的是为了使用流的各个方法 // 2. filter() 传入的是Predicate，返回boolean值 // 3. collect() 传入Collector，将数据收集到集合 // 4. map操作：希望给过滤得到的person对象加入cat对象，原list中的数据也会改变 // 5. sorted() 传入Comparator（object1, object2） List<Person> list2 = list.stream().filter(person -> { return person.getId() % 2 != 0; }).map(person -> { Cat cat = new Cat(person.getId() + 100, "小花猫", "橘色"); person.setCat(cat); return person; }).sorted((p1, p2) -> { return p1.getId() - p2.getId(); // 按照id升序排列 //return p2.getId() - p1.getId(); // 按照id降序排列 //return p2.getAge() - p1.getAge(); // 按照年龄从大到小排列 }).collect(Collectors.toList()); System.out.println("list2==>" + list2); System.out.println("list==>" + list); //分割线条，测试上面代码时请注释上面这段代码 // 其他常用的stream API // limit使用 // 需求：要显示list集合的前两个数据 list.stream().limit(2).forEach(person -> { System.out.println(person); }); // count使用 long count = list.stream().count(); System.out.println(count); // 先过滤再counter long count1 = list.stream().filter(person -> { return person.getAge() > 10; }).count(); System.out.println(count1); } } // Person类 class Person { private Integer id; private String name; private Integer age; private Cat cat; public Person(Integer id, String name, Integer age) { this.id = id; this.name = name; this.age = age; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Cat getCat() { return cat; } public void setCat(Cat cat) { this.cat = cat; } @Override public String toString() { return "Person{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + ", cat=" + cat + '}'; } } // Cat类 class Cat { private Integer id; private String name; private String color; public Cat(Integer id, String name, String color) { this.id = id; this.name = name; this.color = color; } @Override public String toString() { return "Cat{" + "id=" + id + ", name='" + name + '\'' + ", color='" + color + '\'' + '}'; } } package com.zuke.zukeliving.commodity.learnTest; import java.util.ArrayList; import java.util.List; import java.util.Map; import java.util.stream.Collectors; //流式计算：将集合转成map public class T2 { public static void main(String[] args) { //先构建一个集合 ArrayList<stu> stus = new ArrayList<>(); stus.add(new stu(100, "zk1", "中国1", "game1")); stus.add(new stu(200, "zk2", "中国2", "game2")); stus.add(new stu(300, "zk3", "中国3", "game3")); stus.add(new stu(400, "zk4", "中国4", "game4")); //需求 //将stu -> map k-string v-List<stu2> //stu(100,"zk1","中国1","game1") -> 100 -> 两个stu2【("zk1","game1"),("zk1-克隆","game1")】 Map<String, List<stu2>> maps = stus.stream().collect(Collectors.toMap(k -> { return k.getId().toString(); }, v -> { ArrayList<stu2> list = new ArrayList<>(); list.add(new stu2(v.getName(), v.getHobby())); list.add(new stu2(v.getName() + "-克隆", v.getHobby())); return list; })); System.out.println(maps); } } class stu { private Integer id; private String name; private String address; private String hobby; @Override public String toString() { return "stu{" + "id=" + id + ", name='" + name + '\'' + ", address='" + address + '\'' + ", hobby='" + hobby + '\'' + '}'; } public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public String getHobby() { return hobby; } public void setHobby(String hobby) { this.hobby = hobby; } public stu(Integer id, String name, String address, String hobby) { this.id = id; this.name = name; this.address = address; this.hobby = hobby; } public stu() { } } class stu2 { private String name; private String hobby; @Override public String toString() { return "stu2{" + "name='" + name + '\'' + ", hobby='" + hobby + '\'' + '}'; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getHobby() { return hobby; } public void setHobby(String hobby) { this.hobby = hobby; } public stu2(String name, String hobby) { this.name = name; this.hobby = hobby; } public stu2() { } }