Original ArrayList being modified when another ArrayList set equal to it is changed

Question

I am using an ArrayList for a program, called wordList. I have a separate ArrayList for another method, called smallestWords. I do "smallestWords = arrayList" in order to have a copy of wordList that I can modify without affecting the original. However, whenever I modify smallestWords, it also modifies wordList, which is causing me issues. I'm assuming it's because setting smallestWords equal to wordList just sets it equal to that memory location, since it's an abstract data type, and gets passed by reference.

How can I make it so I get a copy of the data without being able to modify it? If you want to see the actual code for the program just ask.

Are you actually copying the list or are you just assigning another variable to it? — khelwood, Nov 03 '14 at 22:56

score 2 · Answer 1 · answered Nov 03 '14 at 22:58

2

You are not copying with smallestWords = arrayList . You are just assigning the same ArrayList to smallestWords

You should use below method to copy:

List<String> smallestWords = new ArrayList<String>(arrayList);

answered Nov 03 '14 at 22:58

Salih Erikci

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score 0 · Answer 2 · answered Nov 03 '14 at 22:59

0

If you want to make a copy of an ArrayList, you can use:

ArrayList smallestWords = new ArrayList(wordList);

(insert generic type parameters as appropriate)

answered Nov 03 '14 at 22:59

khelwood

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Original ArrayList being modified when another ArrayList set equal to it is changed

2 Answers2