1.   ArrayList<Person> list = new ArrayList<>();
    2.         list.add(new Person("a", 1));
    3.         list.add(new Person("b", 12));
    4.         list.add(new Person("c", 3));
    5.         Map<String, Integer> map = list.stream().collect(Collectors.toMap(new Function<Person, String>() {
    6.             @Override
    7.             public String apply(Person person) {
    8.                 return person.name;
    9.             }
    10.         }, new Function<Person, Integer>() {
    11.             @Override
    12.             public Integer apply(Person person) {
    13.                 return person.age;
    14.             }
    15.         }));
    17.         for (String s : map.keySet()) {
    18.             System.out.println(s + "--" + map.get(s));
    19.         }
    22.     }

    lambda表达式写法

    1.  Map<String, Integer> map2 = list.stream().collect(Collectors.toMap(person -> person.name, person -> person.age));
    2.         for (String s : map2.keySet()) {
    3.             System.out.println(s + "--" + map2.get(s));
    4.         }

    Person.java
    StreamTest2.java