Java casting in if/else block

Question

I'm trying to take 2 values and cast them to Integer or Double, but I'm unable to do so in a simple manner as described below, because the variable declaration can't be done inside a block statement:

if (args.get(0) instanceof Integer) {
    Integer left = (Integer) args.get(0);
} else {
    Double left = (Double) args.get(0);
}

if (args.get(1) instanceof Integer) {
    Integer right = (Integer) args.get(1);
} else {
    Double right = (Double) args.get(1)
}

return left + right; // this is not allowed

Of course, a trivial solution would be to exhaust all 4 combinations:

if (args.get(0) instanceof Integer && args.get(1) instanceof Integer) {
    return ((Integer) args.get(0)) + ((Integer) args.get(1));
} else if ...

However, I assume there is a simple and well-known design pattern to achieve what I want much more eloquently.

Perfect link: stackoverflow.com/questions/9205131/… (related stackoverflow.com/questions/19463138/… also stackoverflow.com/questions/16040556/…) — Tunaki
– Tunaki, Commented May 6, 2016 at 17:56
@Tunaki. Thank you for your response. I'm however unable to see how the link you provided could help my case. Double and Integer are both derived from Number, but I can't add 2 instances of Number together with a binary operator. What am i missing? — stensootla
– stensootla, Commented May 6, 2016 at 18:02
Going through an awful lot of work to do something that is easily handled by formatting the result as needed. — dbugger
– dbugger, Commented May 6, 2016 at 18:03

shmosel · Accepted Answer · 2016-05-06 18:05:52Z

5

You don't have to exhaust all 4 options, because only one of them results in an integer:

Number left = (Number)args.get(0);  // not sure if casting is necessary here
Number right = (Number)args.get(1); // since I don't know the type of your list
if (left instanceof Integer && right instanceof Integer) {
    // if both operands are Integer, return an Integer
    return left.intValue() + right.intValue();
} else {
    // if any of the operands is Double, the result must be Double
    return left.doubleValue() + right.doubleValue();
}

answered May 6, 2016 at 18:05

shmosel

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