CODEWITHSUNDEEP
javavariablesdeclaration
Justin
Justin

Reputation: 31

Declare new class from a Variable in Java

I would like to know if there is a way to do something like this in Java:

Integer a = new Integer(2);
a.getClass() newVariable = new Integer(4);

My question is can I declare the type of a new variable by using a variable?

Upvotes: 0

Views: 224

Answers (2)

Jean-François Savard
Jean-François Savard

Reputation: 21004

It is not possible to specify the type by retrieving it from an other variable.

Note that the reflection tutorial of Oracle provide some methods that would simulate it. It will allow you to instantiate an object by specifying it type as a class. But that won't allow you to first specify the object type by retrieving it from the variable.

You might want to have a look at generics which would probably help you fix the hidden problem that made you ask this question.

A simple example would be

public class Foo<T> {
    private T t;

    public void set(T t) { this.t = t; }
    public T get() { return t; }
}

Note that T stands for Type as per the documentation.

@param the type of the value being boxed

So you can give any type.

You can also specify the extends of the type, which kind of give you some security.

class Foo<T extends Integer>

Upvotes: 2

T.J. Crowder
T.J. Crowder

Reputation: 1073978

No, you cannot base the type of a variable on the type of another variable like that.

Depending on your real goal, you might be able to use Java's generics to get around your reason for feeling you want to do that, but it depends a lot on what your real end goal is. For instance, if this is all in class Foo, you could parameterize it, and then use the parameter in both places:

class Foo<T> {
    public method doSomething() {
        T a = /*...*/;
        T newVariable = /*...*/;
   }
}

Then:

Foo<Integer> f = new Foo<Integer>();

...results in an f with a doSomething that works with and returns Integers.

Note the /*...*/ after the = in the above: I can't do new T() there, which is a famous limitation of Java's generics. The values for a and newVariable would have to come from somewhere (arguments to the method, for instance, or data members, etc.).

More about generics here, again depending on whether they really help with what you're ultimately trying to do.

Upvotes: 1

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