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Charismatic
Asked:2022-06-12 03:07:22 +0000 UTC2022-06-12 03:07:22 +0000 UTC

java.util.ConcurrentModificationException

  • 772
public class StudentMain {

    public static void main(String[] args) throws IOException {

        StudentService ss = new StudentService();
        List<Student<Integer,String,Integer,Double,Boolean>> students = new ArrayList<>();
        for (int i = 0; i < 10_000; i++) {
            students.add(new Student<>(ss.getNumber(),ss.getNameFromFileOutSide(), ss.getAge(), ss.getRating(),ss.getOlympic()));
        }
        List<Student<Integer, String, Integer, Double, Boolean>> ageEqualOrHigherTwelve;
        ageEqualOrHigherTwelve = students;

        Iterator<Student<Integer, String, Integer, Double, Boolean>> iterator = ageEqualOrHigherTwelve.iterator();
        for (Iterator<Student<Integer, String, Integer, Double, Boolean>> it = iterator; it.hasNext(); ) {
            Student<Integer, String, Integer, Double, Boolean> student = it.next();
            if (student.getA()>=12&&student.getR()>=8) {
                ageEqualOrHigherTwelve.add(student);
            }
        }
        System.out.println(ageEqualOrHigherTwelve);

    }
    }

为什么会抛出异常？以及如何解决？

java

2 个回答

  1. Best Answer

    为什么会抛出异常？

    因为代码为此做了所有事情 - 集合ageEqualOrHigherTwelve本质上与student迭代器用于迭代的列表相同，在这种情况下，更改学生列表时的迭代结果可能是不可预测的。

    如果您需要为给定条件获取过滤的学生列表，只需创建一个新的结果列表：

    List<Student<Integer, String, Integer, Double, Boolean>> ageEqualOrHigherTwelve = new ArrayList<>();

    然后您可以安全地为其添加适当的值。

    或者您可以只使用 Stream API 而无需创建迭代器：

    List<Student<Integer, String, Integer, Double, Boolean>> ageEqualOrHigherTwelve = students
    .stream()
    .filter(student -> student.getA() >= 12 && student.getR() >= 8)
    .collect(Collectors.toList());
    • 1 
  2. ageEqualOrHigherTwelve = new ArrayList<>();

Iterator<Student<Integer, String, Integer, Double, Boolean>> iterator = students.iterator();
    • 1

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