java8集合的流式操作-实用案例（二）

1、map(Student::getStuName).distinct() 集合中对象是否存在某个字段重复

        // map(Student::getStuName).distinct() 集合中对象是否存在某个字段重复
        List<Student> studentList = new ArrayList<>();
        studentList.add(new Student(1,"张三"));
        studentList.add(new Student(2,"李四"));
        studentList.add(new Student(3,"张三"));
        // map获取某字段，与distinct().count结合，判断是否存在重复
        long count = studentList.stream().map(Student::getStuName).distinct().count();
        if (count != studentList.size()) {
   
            System.out.println("存在重复stuName的student");
        }

输出结果

存在重复stuName的student

2、Collectors.toMap 获取集合中重复的对象

        // Collectors.toMap 获取集合中重复的对象
        studentList = new ArrayList<>();
        Student zhangSan = new Student(1,"张三");
        studentList.add<