How can I find out if two arguments are instances of the same, but unknown class?

Let us say we have a method which accepts two arguments o1 and o2 of type Object and returns a boolean value. I want this method to return true only when the arguments are instances of the same class, e.g.:

foo(new Integer(4),new Integer(5));

Should return true, however:

foo(new SomeClass(), new SubtypeSomeClass());

should return false and also:

foo(new Integer(3),"zoo");

should return false.

I believe one way is to compare the fully qualified class names:

public boolean foo(Object o1, Object o2){
 Class<? extends Object> c1 = o1.getClass();
 Class<? extends Object> c2 = o2.getClass();
 if(c1.getName().equals(c2.getName()){ return true;}
 return false;  
}

An alternative conditional statement 开发者_StackOverflow中文版would be :

if (c1.isAssignableFrom(c2) && c2.isAssignableFrom(c1)){ return true; }

The latter alternative is rather slow. Are there other alternatives to this problem?

Don't bother with the fully qualified class names - just compare class references:

public boolean foo(Object o1, Object o2) {
    return o1.getClass() == o2.getClass();
}

Classes are essentially unique by name and classloader - so this will return false if the objects are of the same class name but loaded by different classloaders, but that's probably appropriate: they could be completely different classes in all but name! If the classes have the same name and classloader, however, they'll have the same reference.

Note that this will throw a NullPointerException if either o1 or o2 is null, but again that's probably what you want.

Can you qualify rather slow? Compared to what? Also please elaborate your usage scenario? In java the Object api includes a equals/hashCode method paring that should be used to identify equality between objects. It appears as if this is what you may be attempting to find, ie:

new Integer(4).equals(new Integer(5))

In this case, the best implementation for overriding equals in SomeClass is as follows:

public boolean equals(Object obj) {
    if (obj instanceof SomeClass) {
        return ((SomeClass) obj).identityField.equals(identityField);
    }
    return false;
}
public int hashCode() {
    return 31 * identity.hashCode();
}

Making sure you provide an identity within your object.