Receive class type and argument and return instance

July 12, 2023

I know this maybe be a duplicate but i’ve been scouring through stack overflow but i’m still yet to find an answer.

What i want to do is accept a class type as argument and return an instance of that class. Here is what i’m trying to do

class A {

}

class B {

    /* 
    * Takes class type as argument and returns an instance of that class
    */
    public static Object createInstanceOfAnyClass(Class<?> klassType) {
        return new klassType();
    }
}

public class Main {
    public static void main(String[] args) {
        A a = B.createInstanceOfAnyClass(A);  // pass class(type) A and receive an instance of A
    }
}

Basically, after passing Class<A> as argument to B.createInstanceOfAnyClass, i should get an instance of class A.

>Solution :

Use a generic type parameter for the return type so you don’t need to cast the result from Object.

.getDeclaredConstructor().newInstance() can be used on a Class object to create an instance using the no-argument constructor.

public static <T> T createInstanceOfAnyClass(Class<T> klassType) {
    try {
        return klassType.getDeclaredConstructor().newInstance();
    } catch (ReflectiveOperationException e) {
        throw new RuntimeException(e); // or other handling
    }
}
// Usage:
A a = B.createInstanceOfAnyClass(A.class);