CODEWITHSUNDEEP
javagenericsobjectcastingcomparable
nabil
nabil

Reputation: 904

how to send Object to method as comparable parameter?

I have this provided function that I want to use:

boolean check(Comparable<Object> obj1, Comparable<Object> obj2) {
   // do something
}

and I have:

Object obj1,obj2;

that I want to send to method check, how can I cast or convert the two Objects to Comparables ?

I wish I was clear, thank you.

Upvotes: 0

Views: 2038

Answers (4)

Edwin Dalorzo
Edwin Dalorzo

Reputation: 78589

Well, if your two object references are truly pointing to Comparable objects, you could simply do

check((Comparable<Object>) obj1, (Comparable<Object>) obj2);

-EDIT-

Of course this generates a warning, you are basically telling the compiler that you know better. The compiler is warning you that there is chance you could be wrong if obj is not truly what you said it was in terms of its generic type parameter. You can tell your compiler to shut up, that you are really, really sure, using an annotation:

@SuppressWarnings("unchecked")
Comparable<Object> cmp1 = (Comparable<Object>) obj;
@SuppressWarnings("unchecked")
Comparable<Object> cmp2 = (Comparable<Object>) obj;     
check(cmp1,cmp2);

When you use a @SupressWarning annotation you typically add a comment indicating why you are so positively sure that the unsafe cast will always succeed.

Upvotes: 3

alaster
alaster

Reputation: 4171

Objects you want to send to this method must be type of Comparable. So they must implement Comparable interface.

Comparable obj1 = new Comparable() {
    // ... realize compare method
}

then you can send this object to your function.

If you have your own class implement interface this way:

public class MyClass implements Comparable {
    // realize compare method
}

Upvotes: 0

JB Nizet
JB Nizet

Reputation: 691765

As you said:

check((Comparable<Object>) obj1, (Comparable<Object>) obj2);

That said, I don't know of any class that implements Comparable<Object>. The method should probably take Comparable<?> as arguments rather than Comparable<Object>.

Upvotes: 4

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285405

Don't use 

Object obj1, obj2;

but rather

Comparable obj1, obj2;

Upvotes: 2

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