Stream流之Collectors.toMap

public class Demo {

    public static void main(String[] args) {
    
        List<Pair<String, Double>> pairArrayList = new ArrayList<>(3);
        pairArrayList.add(new Pair<>("version", 12.10));
        pairArrayList.add(new Pair<>("version", 12.09));
        pairArrayList.add(new Pair<>("demo", 6.28));
        pairArrayList.add(new Pair<>("demo", 12.19));
        
        //根据key相同,把value进行处理,key相同的键值对只存储一个
        Map<String, Double> map = pairArrayList.stream()
                .collect(Collectors.toMap(Pair::getKey, Pair::getValue, (v1 , v2) -> v1>v2?v1:v2));
        System.out.println(map);

        List<Person> personList = new ArrayList<>(3);
        personList.add(new Person("demo",15));
        personList.add(new Person("bob",19));
        personList.add(new Person("tom",16));

        //以name为key存储person对象
        Map<String ,Person> personMap = personList.stream().collect(Collectors.toMap(Person::getName,person ->person));
        System.out.println(personMap);

        //以name为key存储age
        Map<String, Integer> collect = personList.stream().collect(Collectors.toMap(Person::getName, person -> person.getAge()));
        System.out.println(personMap.get("bob"));
    }
}
class Person{
    private String name;
    private Integer age;

    public Person() {
    }

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

    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;
    }

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