java arraylist sum of objects

Question

If the type of my ArrayList is not an Integer (They are called Objects), how can I get the sum inside of the list? newlist.get(i) will return Object and I can't sum with "sum".

ArrayList newlist = new ArrayList();
newlist.add(1);
newlist.add(2);
newlist.add(3);
newlist.add(4);

for (int i = 0; i < newlist.size(); i++) {
    sum = newlist.get(i) + sum;
}

What in Object do you even want to sum? And never ever use ArrayList without type specifier. — SkryptX
– SkryptX, Commented Oct 4, 2015 at 15:51

Mureinik · Accepted Answer · 2015-10-04 15:42:17Z

2

You could check the runtime type and downcast the Integers:

for(int i = 0; i < newlist.size(); i++){
    Object o = newlist.get(i);
    if (o instanceof Integer) {
        sum += ((Integer) o);
    }
}

answered Oct 4, 2015 at 15:42

Mureinik

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3 Comments

nixiehi Over a year ago

thank you :) If I have more reputation ,my vote will change soon

Mureinik Over a year ago

@nixiehi you can always accept an answer (the "check" sign), regardless of your rep

SkryptX Over a year ago

@nixiehi Is this answer even the thing you wanted? Is the ArrayList really mixed?? I mean of course it works like that but it's not what's best if the ArrayList is just filled with Integers...

SkryptX · Accepted Answer · 2015-10-04 15:57:46Z

0

If the ArrayList is just filled with Integers then your code would be like this:

ArrayList<Integer> newlist = new ArrayList<Integer>();
newlist.add(1);
newlist.add(2);
newlist.add(3);
newlist.add(4);

int sum = 0;

for (int i = 0; i < newlist.size(); i++) {
    sum = newlist.get(i) + sum;
}

answered Oct 4, 2015 at 15:57

SkryptX

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