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Andrey
Andrey

Reputation: 201

Java: ArrayList: Determine if entry exists by its index

How can I check if value exist in ArrayList by its index?

Java offers contains(Object) method, but no contains(Integer index) method

Thank you

Upvotes: 0

Views: 10341

Answers (4)

djjudjju
djjudjju

Reputation: 1

Maybe you should consider using a HashMap instead of an ArrayList. There is a reason why the method exist(int index) is not implemented for ArrayList (mainly because it takes to much memory to implement an ArrayList for specifics indexes): 

int i = 3; int j = 4;
HashMap<Integer, Integer> hm = new HashMap<Integer, Integer>();
hm.put(3, 4);
hm.containsKey(3);

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533530

If you have a sparse array (which can contain null values) you might want to check for this as well.

public static boolean isSet(List<?> list, int index) {
   return index >=0 && index < list.size() && list.get(index) != null;
}

Not sure why you would want the index to be Integer type but if you do you should check for null as well. Allowing a null value is the only good reason to have an Integer type.

public static boolean isSet(List<?> list, Integer index) {
   return index != null && index >=0 && index < list.size() && list.get(index) != null;
}

Upvotes: 3

NawaMan
NawaMan

Reputation: 25687

How can I check if value exist in ArrayList by its index?

Try this:

int     aIndex = ...;
boolean aIsExistByIndex = (aIndex >= 0) && (aIndex < AL.size())

Hope this help :-p

Upvotes: 1

T.J. Crowder
T.J. Crowder

Reputation: 1074465

Not at all sure what your question is. You talk about seeing if an entry "exists" but then you talk about Java lacking a remove(Object index) method.

Regarding remove: There's the remove(int) method on the List interface implemented by ArrayList. (Java Lists are indexed by int, not by Object.)

Regarding whether an entry "exists" at a given index, if the list's size() method is greater than the index (and the index is non-negative), then there's an entry at that index:

if (index >= 0 && index < list.size()) {
    // An entry exists; hey, let's remove it
    list.remove(index);
}

Upvotes: 5

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