public static void main(String[] args) {
List studentList1 =new ArrayList<>();
for (int i =0; i <10; i++) {
studentList1.add(new Student(i, i%3 +"Alice"));
}
long count = studentList1.stream().map(Student::getAge).count();
int reduce1 = studentList1.stream().map(Student::getAge).reduce(0, Integer::sum).intValue();
System.out.println(count==reduce1);
//可以后排序
List collect3 = studentList1.stream().map(Student::getName).limit(10).skip(3).sorted(String::compareTo).collect(Collectors.toList());
List collect4 = studentList1.stream().map(Student::getName).limit(10).skip(3)
.sorted((o1, o2) -> o1.compareTo(o2)).collect(Collectors.toList());
System.out.println(collect3);
Student student1 =new Student(16, "Alice");
Student student2 =new Student(16, "Bob");
Student student3 =new Student(17, "Cherry");
Student student4 =new Student(17, "Delivery");
List studentList =new ArrayList<>();
studentList.add(student1);
studentList.add(student2);
studentList.add(student3);
studentList.add(student4);
String reduce = studentList.stream().map(Student::getName).reduce("", String::concat);
System.out.println(reduce);
//flatMap 对象是tream
List collect = studentList.stream().flatMap(t -> Arrays.asList(t).stream()).collect(Collectors.toList());
System.out.println(collect);
//map换对象
List collect1 = studentList.stream().map(t -> ABC.builder().age(t.getAge()).build()).collect(Collectors.toList());
System.out.println(collect);
// List to Map
// 1. 首先使用`Collectors.groupingBy()根据某个字段进行分组`
Map> collect2 = studentList.stream().collect(Collectors.groupingBy(Student::getAge,
Collectors.mapping(t -> t, Collectors.toList())));
System.out.println(collect);
// 2. 分组的同时使用`Collectors.mapping()`将分组后的数据组织起来
Map> map = studentList.stream()
.collect(
Collectors.groupingBy(Student::getAge,
Collectors.mapping(Student::getName, Collectors.toList())));
System.out.println(map);
// 这里将分组后的数据组织成一个Map
Map> map2 = studentList.stream()
.collect(
Collectors.groupingBy(Student::getAge,
Collectors.toMap(Student::getName, student -> student)));
System.out.println(map2);
}
}
class Student {
private Stringname;
private Integerage;
Student(Integer age, String name) {
this.age = age;
this.name = name;
}
public IntegergetAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public StringgetName() {
System.out.println(name);
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public StringtoString() {
return "Student{" +
"name='" +name +'\'' +
", age=" +age +
'}';
}
}
@Builder
@Getter
@Setter
@ToString
class ABC {
private Stringname;
private Integerage;
}
