when modCount is initialized in java.util.ArrayList?

I want to know when the field modCount of java.util.ArrayList is initialized.From the source code of java.util.ArrayList,we know the field modCount is inherited from
java.util.AbstractList. And in the private inner class of java.util.ArrayList named Itr,its field expectedModCount is assigned from modCout，as shown below

enter image description here

In a demo,I debugged and found that itr.expectedModCount has been initialized.Because the value of expectedModCount is from modCount.So I looked up the source code to find when modCount is initialized,but failed.

enter image description here

asked Nov 14 '18 at 13:20

Zhi Zheng

414

add a comment |

enter image description here

asked Nov 14 '18 at 13:20

Zhi Zheng

414

add a comment |

enter image description here

asked Nov 14 '18 at 13:20

Zhi Zheng

414

enter image description here

java iterator

asked Nov 14 '18 at 13:20

Zhi Zheng

414

asked Nov 14 '18 at 13:20

Zhi Zheng

414

asked Nov 14 '18 at 13:20

Zhi Zheng

414

asked Nov 14 '18 at 13:20

Zhi Zheng

414

asked Nov 14 '18 at 13:20

Zhi Zheng

414

add a comment |

2 Answers
2

active

oldest

votes

It is initialized to 0 (note that it's an instance variable of the AbstractList super-class):

protected transient int modCount = 0;

and incremented in several places in which the List is structurally modified (i.e. elements are added or removed).

For example:

public E remove(int index) 
 rangeCheck(index);

 modCount++;
 ....

Note that the Itr class is an inner class of ArrayList, and therefore it has access to the members of the enclosing ArrayList instance (which includes the modCount instance variable of the AbstractList super-class).

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

add a comment |

When I lookup where modCount is located I can find it, it's located inside java.util.AbstractList and is declared as:

protected transient int modCount = 0;

This means that it's initialized when it's declared.

answered Nov 14 '18 at 13:27

Mark

3,70921126

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

add a comment |

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2 Answers
2

active

oldest

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2 Answers
2

active

oldest

votes

It is initialized to 0 (note that it's an instance variable of the AbstractList super-class):

protected transient int modCount = 0;

and incremented in several places in which the List is structurally modified (i.e. elements are added or removed).

For example:

public E remove(int index) 
 rangeCheck(index);

 modCount++;
 ....

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

add a comment |

It is initialized to 0 (note that it's an instance variable of the AbstractList super-class):

protected transient int modCount = 0;

and incremented in several places in which the List is structurally modified (i.e. elements are added or removed).

For example:

public E remove(int index) 
 rangeCheck(index);

 modCount++;
 ....

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

add a comment |

It is initialized to 0 (note that it's an instance variable of the AbstractList super-class):

protected transient int modCount = 0;

and incremented in several places in which the List is structurally modified (i.e. elements are added or removed).

For example:

public E remove(int index) 
 rangeCheck(index);

 modCount++;
 ....

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

It is initialized to 0 (note that it's an instance variable of the AbstractList super-class):

protected transient int modCount = 0;

and incremented in several places in which the List is structurally modified (i.e. elements are added or removed).

For example:

public E remove(int index) 
 rangeCheck(index);

 modCount++;
 ....

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

edited Nov 14 '18 at 13:29

answered Nov 14 '18 at 13:23

Eran

288k37468558

answered Nov 14 '18 at 13:23

Eran

288k37468558

answered Nov 14 '18 at 13:23

Eran

288k37468558

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

add a comment |

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

Thanks for your help.But I still have a doubt when I debugged,I found taht the expectedModCount instance varaible of the Itr class did not equal to the value of modCount instance variable of the ArrayList.Because, in the source coe,filed expectedModCount of Itr given the value of modCount.They should be equal ，in theory

– Zhi Zheng
Nov 14 '18 at 14:20

@ZhiZheng they are equal when the iterator is created. If you perform structural modifications on the ArrayList while iterating over it (not including calling Iterator's remove method, which is allowed), the modCount be be incremented and will no longer be equal to the Iterator's expectedModCount. That's how the Iterator knows you did something wrong, which allows it to fail fast (by throwing ConcurrentModificationException).

– Eran
Nov 14 '18 at 14:23

Thank you very much,I think you are right.I will study it carefully again

– Zhi Zheng
Nov 14 '18 at 14:41

add a comment |

When I lookup where modCount is located I can find it, it's located inside java.util.AbstractList and is declared as:

protected transient int modCount = 0;

This means that it's initialized when it's declared.

answered Nov 14 '18 at 13:27

Mark

3,70921126

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

add a comment |

When I lookup where modCount is located I can find it, it's located inside java.util.AbstractList and is declared as:

protected transient int modCount = 0;

This means that it's initialized when it's declared.

answered Nov 14 '18 at 13:27

Mark

3,70921126

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

add a comment |

When I lookup where modCount is located I can find it, it's located inside java.util.AbstractList and is declared as:

protected transient int modCount = 0;

This means that it's initialized when it's declared.

answered Nov 14 '18 at 13:27

Mark

3,70921126

When I lookup where modCount is located I can find it, it's located inside java.util.AbstractList and is declared as:

protected transient int modCount = 0;

This means that it's initialized when it's declared.

answered Nov 14 '18 at 13:27

Mark

3,70921126

answered Nov 14 '18 at 13:27

Mark

3,70921126

answered Nov 14 '18 at 13:27

Mark

3,70921126

answered Nov 14 '18 at 13:27

Mark

3,70921126

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

add a comment |

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

Yes ,it is,thanks

– Zhi Zheng
Nov 14 '18 at 14:42

add a comment |

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