list集合遍历今日遇到问题，刚开始用增强for循环，删除元素报错了，后面改用迭代器，下边是遍历的方式和特点

/**

* 使用增强的for循环

* 在循环过程中从List中删除元素以后，继续循环List时会报ConcurrentModificationException

*/

public void listRemove() {

List<Student> students = this.getStudents();

for (Student stu : students) {

if (stu.getId() == 2)

students.remove(stu);

}

}

/**

* 像这种使用增强的for循环对List进行遍历删除，但删除之后马上就跳出的也不会出现异常

*/

public void listRemoveBreak() {

List<Student> students = this.getStudents();

for (Student stu : students) {

if (stu.getId() == 2) {

students.remove(stu);

break;

}

}

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

/**

* 这种遍历有可能会遗漏某个元素,因为删除元素后List的size在

* 变化，元素的索引也在变化，比如你循环到第2个元素的时候你把它删了，

* 接下来你去访问第3个元素，实际上访问到的是原先的第4个元素。当访问的元素

* 索引超过了当前的List的size后还会出现数组越界的异常，当然这里不会出现这种异常，

* 因为这里每遍历一次都重新拿了一次当前List的size。

*/

public void listRemove2() {

List<Student> students = this.getStudents();

for (int i=0; i<students.size(); i++) {

if (students.get(i).getId()%3 == 0) {

Student student = students.get(i);

students.remove(student);

}

}

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

/**

* 使用Iterator的方式也可以顺利删除和遍历

*/

public void iteratorRemove() {

List<Student> students = this.getStudents();

System.out.println(students);

Iterator<Student> stuIter = students.iterator();

while (stuIter.hasNext()) {

Student student = stuIter.next();

if (student.getId() % 2 == 0)

//这里要使用Iterator的remove方法移除当前对象，如果使用List的remove方法，则同样会出现ConcurrentModificationException

stuIter.remove();

}

System.out.println(students);

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

public class ListRemove {

public static void main(String args[]) {

ListRemove lr = new ListRemove();

lr.listRemove();

lr.listRemoveBreak();

// lr.listRemove2();

// lr.iteratorRemove();

}

/**

* 使用增强的for循环

* 在循环过程中从List中删除元素以后，继续循环List时会报ConcurrentModificationException

*/

public void listRemove() {

List<Student> students = this.getStudents();

for (Student stu : students) {

if (stu.getId() == 2)

students.remove(stu);

}

}

/**

* 像这种使用增强的for循环对List进行遍历删除，但删除之后马上就跳出的也不会出现异常

*/

public void listRemoveBreak() {

List<Student> students = this.getStudents();

for (Student stu : students) {

if (stu.getId() == 2) {

students.remove(stu);

break;

}

}

}

/**

* 这种不使用增强的for循环，每次重新获取list的size遍历的情况运行时不会报错，但是可能删除的结果是错的。

*/

public void listRemove2() {

List<Student> students = this.getStudents();

for (int i=0; i<students.size(); i++) {

if (students.get(i).getId()%2 == 0)

students.remove(i);

}

}

/**

* 使用Iterator的方式也可以顺利删除和遍历

*/

public void iteratorRemove() {

List<Student> students = this.getStudents();

System.out.println(students);

Iterator<Student> stuIter = students.iterator();

while (stuIter.hasNext()) {

Student student = stuIter.next();

if (student.getId() % 2 == 0)

stuIter.remove();

}

System.out.println(students);

}

private List<Student> getStudents() {

List<Student> students = new ArrayList<Student>() {

{

int i = 0;

while (i++ < 10) {

Student student = new Student(i, "201200" + i, "name_" + i);

this.add(student);

}

}

};

return students;

}

}

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

public class Student {

private int id;

private String stuNo;

private String name;

public Student() {

}

public Student(int id, String stuNo, String name) {

this.id = id;

this.stuNo = stuNo;

this.name = name;

}

public int getId() {

return id;

}

public void setId(int id) {

this.id = id;

}

public String getStuNo() {

return stuNo;

}

public void setStuNo(String stuNo) {

this.stuNo = stuNo;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

@Override

public String toString() {

return "Student [id=" + id + ", name=" + name + ", stuNo=" + stuNo

+ "]";

}

}