How to check if the value is integer in java?

Question

I'm using some API by restTemplate. The API returns a key whose type is integer.

But I'm not sure of that value, so I want to check whether the key is really an integer or not. I think it might be a string.

What is the best way of checking if the value is really integer?

added: I mean that some API might return value like below. {id : 10} or {id : "10"}

Java is statically typed, so the API must have a fixed return type. I don't see what the point of this question is. — NullUserException, Dec 01 '11 at 04:43
Is the return type actually `Integer` or is it a `string` representation of a number? — AusCBloke, Dec 01 '11 at 04:45
@NullUserException: The API might return an `Object` or something silly like that. — Chris Parton, Dec 01 '11 at 04:46
@NullUserException: Yeah, hence the reason I said "silly" in my comment :) It would still be possible nonetheless. Maybe the API is a poorly-built socket wrapper? `ObjectInputStream`s return an Object when reading across a socket via `readObject()`. That's the only reason I could see an `Object` being returned. — Chris Parton, Dec 01 '11 at 04:51

score 11 · Answer 1 · answered Dec 01 '11 at 04:48

If what you receive is a String, you can try to parse it into an integer, if it fails, it's because it was not an integer after all. Something like this:

public static boolean isInteger(String str) {
    try {
        Integer.parseInt(str);
        return true;
    } catch (NumberFormatException nfe) {
        return false;
    }
}

score 9 · Accepted Answer · answered Dec 01 '11 at 04:43

9

Object x = someApi();

if (x instanceof Integer)

Note that if someApi() returns type Integer the only possibilities of something returned are:

an Integer
null

In which case you can:

if (x == null) {
    // not an Integer
} else {
    // yes an Integer
}

answered Dec 01 '11 at 04:43

Bohemian

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This fails for me in Java 7 when the string has other characters in it too. – zeeshan Feb 03 '15 at 19:16

score 2 · Answer 3 · answered Dec 01 '11 at 04:42

2

One possibility is to use Integer.valueOf(String)

answered Dec 01 '11 at 04:42

Raghuram

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This assumes the object is a string. What if it's *actually* an Integer? This is where I don't understand the OP's question: they ask as if the return type is unknown (and unknowable) – NullUserException Dec 01 '11 at 04:46

mprabhat · Answer 4 · 2011-12-01T05:27:21.880

0

Assuming your API return value can either be an Integer or String you can do something like this:

Integer getValue(Object valueFromAPI){
    return (valueFromAPI != null ? Integer.valueOf(valueFromAPI.toString()) : null); 
}

edited Dec 01 '11 at 05:27

answered Dec 01 '11 at 05:20

mprabhat

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How to check if the value is integer in java?

4 Answers4

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