Best way to “negate” an instanceof

Question

I was thinking if there exists a better/nicer way to negate an instanceof in Java. Actually, I\'m doing something like:

if(!(str instanceof String))         


        

Answer 1

If you can use static imports, and your moral code allows them

public class ObjectUtils {
    private final Object obj;
    private ObjectUtils(Object obj) {
        this.obj = obj;
    }

    public static ObjectUtils thisObj(Object obj){
        return new ObjectUtils(obj);
    }

    public boolean isNotA(Class<?> clazz){
        return !clazz.isInstance(obj);
    }
}

And then...

import static notinstanceof.ObjectUtils.*;

public class Main {

    public static void main(String[] args) {
        String a = "";
        if (thisObj(a).isNotA(String.class)) {
            System.out.println("It is not a String");
        }
        if (thisObj(a).isNotA(Integer.class)) {
            System.out.println("It is not an Integer");
        }
    }    
}

This is just a fluent interface exercise, I'd never use that in real life code!
Go for your classic way, it won't confuse anyone else reading your code!

Answer 2

If you find it more understandable, you can do something like this with Java 8 :

public static final Predicate<Object> isInstanceOfTheClass = 
    objectToTest -> objectToTest instanceof TheClass;

public static final Predicate<Object> isNotInstanceOfTheClass = 
    isInstanceOfTheClass.negate(); // or objectToTest -> !(objectToTest instanceof TheClass)

if (isNotInstanceOfTheClass.test(myObject)) {
    // do something
}

Answer 3

I don't know what you imagine when you say "beautiful", but what about this? I personally think it's worse than the classic form you posted, but somebody might like it...

if (str instanceof String == false) { /* ... */ }

Answer 4

You could use the Class.isInstance method:

if(!String.class.isInstance(str)) { /* do Something */ }

... but it is still negated and pretty ugly.

Answer 5

Usually you don't want just an if but an else clause as well.

if(!(str instanceof String)) { /* do Something */ } 
else { /* do something else */ }

can be written as

if(str instanceof String) { /* do Something else */ } 
else { /* do something */ }

Or you can write the code so you don't need to know if its a String or not. e.g.

if(!(str instanceof String)) { str = str.toString(); } 

can be written as

str = str.toString();

Answer 6

ok just my two cents, use a is string method:

public static boolean isString(Object thing) {
    return thing instanceof String;
}

public void someMethod(Object thing){
    if (!isString(thing)) {
        return null;
    }
    log.debug("my thing is valid");
}