Java8

2024-06-25 13:04| 来源: 网络整理| 查看: 265

使用Java8的Stream的distinct方法去重，我们的对象需要实现hashcode()和equals()方法。

把学生类修改后如下：

public class Student { private Long id; private String name; private int age; private Double height; public Student(Long id, String name, int age, Double height) { this.id = id; this.name = name; this.age = age; this.height = height; } public Long getId() { return id; } public void setId(Long id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public Double getHeight() { return height; } public void setHeight(Double height) { this.height = height; } @Override public String toString() { return "Student{" + "id=" + id + ", name='" + name + '\'' + ", age=" + age + ", height=" + height + '}'; } @Override public boolean equals(Object o) { if (this == o) return true; if (o == null || getClass() != o.getClass()) return false; Student student = (Student) o; return age == student.age && Objects.equals(id, student.id) && Objects.equals(name, student.name) && Objects.equals(height, student.height); } @Override public int hashCode() { return Objects.hash(id, name, age, height); } }

测试例子：

import com.top.test.dto.Student; import java.util.*; import java.util.concurrent.ConcurrentHashMap; import java.util.function.Function; import java.util.function.Predicate; import java.util.stream.Collectors; public class ListStreamDistinctTest { public static void main(String[] args) { // 一个集合中放入4个学生对象 List list = new ArrayList(); list.add(new Student(10002L, "ZhangSan", 18, 175.2)); list.add(new Student(10001L, "LiSi", 19, 175.2)); list.add(new Student(10004L, "Peter", 19, 170.8)); list.add(new Student(10004L, "Peter", 19, 170.8)); // 按整个个对象去重 System.out.println("整个对象去重："); list.stream().distinct() .forEach(System.out::println); // 指定某个字段去重 System.out.println("指定age属性去重（方法一）："); list.stream().filter(distinctByKey1(s -> s.getAge())) .forEach(System.out::println); // 方法二（用循环) System.out.println("指定age属性去重（方法二）："); TreeSet students = new TreeSet(Comparator.comparing(s -> s.getAge())); for (Student student : list) { students.add(student); } new ArrayList(students) .forEach(System.out::println); // 方法三：（是方法二的变形），此方法来源于：https://blog.csdn.net/qq_28988969/article/details/81119587 System.out.println("指定age属性去重（方法三）："); list.stream().collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet(Comparator.comparing(s -> s.getAge()))), ArrayList::new)) .forEach(System.out::println); } // 次方法来源于：https://blog.csdn.net/haiyoung/article/details/80934467 static Predicate distinctByKey1(Function keyExtractor) { Map seen = new ConcurrentHashMap(); return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null; } }

执行结果：

整个对象去重： Student{id=10002, name='ZhangSan', age=18, height=175.2} Student{id=10001, name='LiSi', age=19, height=175.2} Student{id=10004, name='Peter', age=19, height=170.8} 指定age属性去重（方法一）： Student{id=10002, name='ZhangSan', age=18, height=175.2} Student{id=10001, name='LiSi', age=19, height=175.2} 指定age属性去重（方法二）： Student{id=10002, name='ZhangSan', age=18, height=175.2} Student{id=10001, name='LiSi', age=19, height=175.2} 指定age属性去重（方法三）： Student{id=10002, name='ZhangSan', age=18, height=175.2} Student{id=10001, name='LiSi', age=19, height=175.2}

Lambda表达式和函数式接口看不懂的，可以参考之前的文章： Java8 Lambda表达式和函数式编程原理详解

沪漂程序员。坚持写博客，如果觉得还可以的话，给个小星星哦，你的支持就是我创作的动力。

个人微信公众号：“Java尖子生”，阅读更多干货。关注公众号，领取学习、面试资料。加技术讨论群。

阅读更多我的相关内容 Java8 Lambda表达式和函数式编程原理详解 Java8方法引用，示例讲解 Java8-默认方法和默认静态方法 Java8-Stream流操作List排序(完整实例讲解）

【本文地址】

Java8

Java8

今日新闻

推荐新闻