Java8中的Stream操作集合

最新推荐文章于 2023-03-22 11:27:16 发布

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本文详细介绍了Java Stream API中的四个核心操作：filter用于筛选符合条件的元素；map用于将元素转换为另一种形式；distinct用于去除重复元素；anyMatch用于检查是否至少有一个元素符合指定条件。通过具体示例，展示了如何使用这些操作高效地处理集合数据。

   1、filter：筛选
       Student stu1 = new Student(1, 19, "张亮");
Student stu2 = new Student(2, 29, "周文");
Student stu3 = new Student(3, 23, "王彪");
List<Student> stuList = new ArrayList<>();
stuList.add(stu1);
stuList.add(stu2);
stuList.add(stu3);
//筛选年龄大于22岁的学生
List<Student> students = stuList
.stream()
.filter(student -> student.getAge() > 22)
.collect(Collectors.toList());
       //结果students：[Student(id=2, age=29, name=周文), Student(id=3, age=23, name=王彪)]

   2、map：转换
       Student stu1 = new Student(1, 19, "张亮");
Student stu2 = new Student(2, 29, "周文");
Student stu3 = new Student(3, 23, "王彪");
List<Student> stuList = new ArrayList<>();
stuList.add(stu1);
stuList.add(stu2);
stuList.add(stu3);
       List<String> names = stuList
                   .stream()
                   .map(student -> student.getName())
                   .collect(Collectors.toList());
   //结果names：[张亮, 周文, 王彪]

   3、distinct：去重
   Student stu1 = new Student(1, 19, "张亮");
Student stu2 = new Student(2, 29, "周文");
Student stu3 = new Student(3, 23, "王彪");
Student stu4 = new Student(1, 19, "张亮");
List<Student> stuList = new ArrayList<>();
stuList.add(stu1);
stuList.add(stu2);
stuList.add(stu3);
List<Student> students = stuList
.stream()
.distinct()
.collect(Collectors.toList());
   //结果students：[Student(id=1, age=19, name=张亮), Student(id=2, age=29, name=周文), Student(id=3, age=23, name=王彪)]

   4、anyMatch：Stream 中任意一个元素符合传入的 predicate，返回 true
       Student stu1 = new Student(1, 19, "张亮");
Student stu2 = new Student(2, 29, "周文");
Student stu3 = new Student(3, 23, "王彪");
List<Student> stuList = new ArrayList<>();
stuList.add(stu1);
stuList.add(stu2);
stuList.add(stu3);
boolean anyMatchFlag = stuList
.stream()
.anyMatch(student -> "王彪".equals(student.getName()));
   //结果anyMatchFlag：true