How can I tell if the elements in an Array List are same or different?

[Mason Wyatt]

I'm trying to verify if all the elements in an array list are same or not. This is my code:

ArrayList<Integer> arr = new ArrayList<>(Arrays.asList(2,2,4,2));
for (int z = 0; z < arr.size(); z++) {          
    if(!arr.get(z++).equals(arr.get(z--))) {
        System.out.println("same"); 
    }else {
        System.out.println("differnt");         
    }
}

[Campbell Ritchie]

. . . and does your code work? What sort of output do you get? Are you suffering any exceptions?
Don't declare your List as ArrayList; declare it as List. Don't call a List arr; it isn't an array. Call it numbers or something like that.
Why have you got the bang sign/not operator in line 3? I think that shouldn't be there.
If you think about the different kinds of collection/data structure available, which you can read about here, you will find a collection type whose size() method will tell you how many distinct elements you have.

[Matt Wong]

the questions is not unique defined - are you try to look for any matches or do you want all entries the same (i cant come up with a usefull case for the latter one)?

also: why get(z++).equals(get(z--))?
simple write: get(z).equals(get(z+1))

if you really want to all entries the same: for(Integer integer : list) ...
this way you make use of List.iterator() - depend on impl of list may faster

[Paul Clapham]

Matt Wong wrote:also: why get(z++).equals(get(z--))?
simple write: get(z).equals(get(z+1))

I'm glad you clarified that, Matt. If I was told to look at that code and see what it did, I would have had to get pencil and paper and spend a minute to figure out the first version. I definitely support writing simple code which other people can understand.

[Paul Clapham]

Samantha Rupasingha wrote:I'm trying to verify if all the elements in an array list are same or not.

Then take the first entry in the list and compare it to all of the other entries. As soon as you find one entry which isn't the same as the first entry, you know the answer is No. If you don't find any, then the answer is Yes.

Your code doesn't do that. Apparently it tries to compare adjacent entries; that would work the same way in that finding a pair of adjacent entries which are different means No, but you can't say Yes until you're finished and haven't said No. (Also you have an off-by-one error whereby you will go past the end of the list and an exception will be thrown.)

[Winston Gutkowski]

Samantha Rupasingha wrote:I'm trying to verify if all the elements in an array list are same or not. This is my code:

I think everyone else has covered it, but the basic problem you have is that the code doesn't do what you meant it to.

And when that happens, sometimes you just have to sit down with a paper and pencil and work out what your loop will do on each iteration.

However (TIP) - DON'T use '++' or '--' more than once in a loop. And if you do, it should usually be inside the 'for' part.

You also need to read Paul's second post. Is that what you want to do? If so, he's given you the solution; if not, you need to explain what you DO want to do.

Winston