How to compare value in array?

Question

Hi, how to compare value in an array?

I have array named list which contains 12 elements. I see if value in index 0 is equal or not equal to value in index 2.

I have tried this code but it doesnt seems to work.

if ((list.get(0)==list.get(2) && list.get(1)==list.get(3)) 
{
   System.out.println("equal")
}

Answer 1

If it's really an array, you want:

if (list[0] == list[2] && list[1] == list[3])

Note that if the array is of reference types, that's comparing by reference identity rather than for equality. You might want:

if (list[0].equals(list[2])) && list[1].equals(list[3]))

Although that will then go bang if any of the values is null. You might want a helper method to cope with this:

public static objectsEqual(Object o1, Object o2)
{
    if (o1 == o2)
    {
        return true;
    }
    if (o1 == null || o2 == null)
    {
        return false;
    }
    return o1.equals(o2);
}

Then:

if (objectsEqual(list[0], list[2]) && objectsEqual(list[1], list[3]))

If you've really got an ArrayList instead of an array then all of the above still holds, just using list.get(x) instead of list[x] in each place.

Answer 2

You are comparing object references, not objects themselves. You need to use a method call. All classes inherit equals() from the root Object class, so it might work:

if(list.get(0).equals(list.get(2)) && list.get(1).equals(list.get(3)))
{
   System.out.println("equal");
}

This article seems to be a good summary of other comparison methods available.

Answer 3

if(list[0] == list[2] && list[1] == list[3]){
    System.out.println("equal");
}

If they are strings:

if(list[0].equals(list[2]) && list[1].equals(list[3])){
    System.out.println("equal");
}