how to add int value to Set<Integer> (HashSet<Integer>)?

Question

I created a set and a random number (type of int) that I want to add to my set:

private Set<Integer> mySet = new HashSet<Integer>(numElements); // capacity of 'numElements'

Random r = new Random();
int rand = r.nextInt(maxVal - minVal + 1) + minVal;
mySet.add(rand); // error: cannot convert int to Integer

so I tried these:

1. mySet.add(rand); // error: no suitable method found for add(int)
2. mySet.add(Integer.valueOf(rand)); //error: cannot find symbol method valueOf(int)
3. mySet.add(new Integer(rand)); // error: type parameter Integer cannot be instantiated directly

They all don't work so how can I add 'rand' to my set?

You should post the complete code. Obviously, you have a type named Integer in your scope, which is different to java.lang.Integer. According to the last error message, it is a type parameter, declared either at the method or at the class containing your code. — Holger
– Holger, Commented Nov 14, 2016 at 17:28

Dez · Accepted Answer · 2016-11-18 01:32:21Z

1

You must create object of type Integer:

Integer intObj = new Integer(i);

being i an int type.

So in your example, it would be something like:

private Set<Integer> mySet = new HashSet<Integer>(numElements); // capacity of 'numElements'

Random r = new Random();
int rand = r.nextInt(maxVal - minVal + 1) + minVal;
mySet.add(new Integer(rand));

edited Nov 18, 2016 at 1:32

answered Nov 13, 2016 at 0:59

Dez

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2 Comments

Maor Cohen Over a year ago

but when I try this: mySet.add(new Integer(rand)); it doesn't work. It's written that "type parameter Integer cannot be instantiated directly". and it doesn't work even if I do this: Integer iRand = new Integer(rand); mySet.add(iRand);

Maor Cohen Over a year ago

ohh I just saw your edit.. so I must create MyInteger class that extends Integer for adding int to Set<Integer>?

Maor Cohen · Accepted Answer · 2016-11-14 01:09:44Z

0

I succeeded to find a solution that solves the problem of all the collections that you try to add them a 'int' value. I created this class:

class Number {
    int number;
    Number(int num) { number = num; }
}

Then, in my code, I used it:

Number number = new Number(index); // index is int type
mySet.add(number); // adding an object into a collection is legal

answered Nov 14, 2016 at 1:09

Maor Cohen

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2 Comments

Holger Over a year ago

Adding an object of your custom type Number to a Set<Integer> is not legal. If that is accepted by the compiler, you have changed the type of your Set beforehand. This is kludging as it doesn’t solve your initial task of creating a Set<Integer>.

Maor Cohen Over a year ago

you're right. I forgot to write it but I changed the Set type from Integer to Number.

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