Stream流简单使用
1 按指定字段获取集合对象中的字段
List<String> idList = initStudentList.stream().map(Student::getId).collect(Collectors.toList());2 按指定字段对集合对象进行排序
List<Student> collect = initStudentList.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList());3 按指定字段对集合对象去重处理
List<Student> collect = initStudentList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(Student::getName))), ArrayList::new));4 对集合对象批量处理
initStudentList.forEach((Student user) ->user.setName(user.getName()+"-123"));5 将集合对象中指定字段转数组
String[] strings = initStudentList.stream().map(Student::getId).toArray(String[]::new);代码如下
学生实体类
public class Student {private String id;private String name;private String sex;private int age;private Date birthday;@Overridepublic String toString() {return "User{" +"id='" + id + '\'' +", name='" + name + '\'' +", sex='" + sex + '\'' +", age=" + age +", birthday=" + birthday +'}';}public String getId() {return id;}public void setId(String id) {this.id = id;}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 Date getBirthday() {return birthday;}public void setBirthday(Date birthday) {this.birthday = birthday;}}初始化集合数据
public static List<Student> initStudentList(){List<Student> initStudentList = new ArrayList<>();for (int i = 0; i < 10; i++) {Student Student = new Student();Student.setId(String.valueOf(i*10));Student.setName("名称"+i);Student.setAge(i+2*i);if (i%3!=0){Student.setSex("男");}else{Student.setSex("女");}Student.setBirthday(new Date(new Random().nextLong()*(369 - 258)*i));initStudentList.add(Student);}// 设置重复名称用户Student Student1 = new Student();Student1.setId(String.valueOf(37));Student1.setName("名称"+3);Student1.setAge(11);Student1.setSex("男");Student1.setBirthday(new Date(new Random().nextLong()*(369 - 258)*2));initStudentList.add(Student1);Student Student2 = new Student();Student2.setId(String.valueOf(58));Student2.setName("名称"+5);Student2.setAge(17);Student2.setSex("女");Student2.setBirthday(new Date(new Random().nextLong()*(369 - 258)*2));initStudentList.add(Student2);return initStudentList;}Test
public class StreamTest {public static void main(String[] args) {List<Student> initStudentList = initStudentList();setOut(initStudentList);System.out.println("-----------------------------------");// 流处理// 1 按指定字段获取集合对象中的字段/*List<String> idList = initStudentList.stream().map(Student::getId).collect(Collectors.toList());System.out.println(idList);*/// 2 按指定字段对集合对象进行排序/*List<Student> collect = initStudentList.stream().sorted(Comparator.comparing(Student::getAge)).collect(Collectors.toList());setOut(collect);*/// 3 按指定字段对集合对象去重处理/*List<Student> collect = initStudentList.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(()->new TreeSet<>(Comparator.comparing(Student::getName))), ArrayList::new));setOut(collect);*/// 4 对集合对象批量处理/*initStudentList.forEach((Student user) ->user.setName(user.getName()+"-123"));setOut(initStudentList);*/// 5 将集合对象中指定字段转数组/*String[] strings = initStudentList.stream().map(Student::getId).toArray(String[]::new);for (String string : strings) {System.out.println(string);}*/}public static void setOut(List<Student> list){for (Student student : list) {System.out.println(student);}}public static List<Student> initStudentList(){List<Student> initStudentList = new ArrayList<>();for (int i = 0; i < 10; i++) {Student Student = new Student();Student.setId(String.valueOf(i*10));Student.setName("名称"+i);Student.setAge(i+2*i);if (i%3!=0){Student.setSex("男");}else{Student.setSex("女");}Student.setBirthday(new Date(new Random().nextLong()*(369 - 258)*i));initStudentList.add(Student);}// 设置重复名称用户Student Student1 = new Student();Student1.setId(String.valueOf(37));Student1.setName("名称"+3);Student1.setAge(11);Student1.setSex("男");Student1.setBirthday(new Date(new Random().nextLong()*(369 - 258)*2));initStudentList.add(Student1);Student Student2 = new Student();Student2.setId(String.valueOf(58));Student2.setName("名称"+5);Student2.setAge(17);Student2.setSex("女");Student2.setBirthday(new Date(new Random().nextLong()*(369 - 258)*2));initStudentList.add(Student2);return initStudentList;}}结果截图1
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结果截图5
