CODEWITHSUNDEEP
javaarraysarraylist
john daniels
john daniels

Reputation: 25

Can I compare the equality of an array with an ArrayList of arrays?

I have arrays of integers:

int[] arrA = {1,2,3,4,5,6,7,8,9};
int[] arrB1= {7,3,4,1,5,8,9,2,6};
int[] arrB2= {9,5,1,4,7,6,8,2,3};
int[] arrB3= {4,6,1,3,8,9,5,7,2};
int[] arrB4= {2,3,1,5,8,9,4,6,7};
int[] arrB5= {1,2,3,4,5,6,7,8,9};

and all the arrBs are added to the list, as follows:

List<int[]> list= new ArrayList<int[]>();

list.add(arrB1);
list.add(arrB2);
list.add(arrB3);
list.add(arrB4);
list.add(arrB5);

and I want to compare the equality of the array arrA with the list of arrays and I did it using this code:

boolean isEqual=false;
for(int index=0; index<list.size(); index++){
    if(list.get(index).equals(arrA)){
          isEqual=true;
    }
    System.out.println(isEqual);
}

I know that arrB5 is equal to arrA but why is it that I always get false? Am I doing the comparison right?

Upvotes: 2

Views: 331

Answers (3)

hanlj
hanlj

Reputation: 1

according to java.sun.com The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true). It doesn't perform an intelligent comparison for most classes unless the class overrides it. It has been defined in a meaningful way for most Java core classes. If it's not defined for a (user) class, it behaves the same as ==. so try Arrays.equals(arrB5,arrA).

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1503489

You're calling equals on arrays - which will just compare by reference, as arrays don't override equals. You want Arrays.equals(int[], int[]) to compare the values within the arrays.

(You don't need deepEquals in this case as you're dealing with int[] - and indeed calling deepEquals wouldn't compile, as an int[] isn't an Object[].)

Upvotes: 7

Khinsu
Khinsu

Reputation: 1487

ArrayUtils.isEquals() from Apache Commons does exactly that. It also handles multi-dimensional arrays.

You also should try Arrays.deepEquals(a, b)

Upvotes: 2

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