How do I return an instance of an object of the same type as the class passed in using Java 6?

Question

I want to return an instance of an object of same type of the Class object passed in. The type passed in can be ANYTHING. Is there a way to do this with Generics?

To

Answer 1

public <C> C getObject(Class<C> c) throws Exception 
{ 
    return c.newInstance(); 
}

Usage Example:

static <C> C getObject(Class<C> c) throws Exception { 
    return c.newInstance();
}

static class Testing {
    {System.out.println("Instantiated");}
    void identify(){ System.out.println("Invoked"); }
}

public static void main(String args[]) throws Exception {
    Testing t = getObject(Testing.class);
    t.identify();
}

Answer 2

I assume you want to create a new instance of that class. This would not be possible using generics (you can't call new T()) and would also be quite limited using reflection.

The reflection approach could be:

//class is a reserved word, so use clazz
public <T> T getObject(Class<T> clazz) {
  try {
    return clazz.newInstance();
  }
  catch( /*a multitude of exceptions that can be thrown by clazz.newInstance()*/ ) {
    //handle exception
  }
}

Note that this only works if the class has a no-argument constructor.

However, the question would by why you need that instead of just calling
new WhatEverClassYouHave().

Answer 3

public Object getObject(Class clazz) {
  return clazz.newInstance();
}

Will create a new object of the specified class. You don't have to use generics for this.

Answer 4

You don't have to implement this method, it's already there:

http://docs.oracle.com/javase/7/docs/api/java/lang/Class.html#newInstance%28%29

Usage:

Class<T> type = ...;
T instance = type.newInstance();

Answer 5

If you aren't trying to do anything fancy with the object during the creation, what's wrong with just using a good old fashioned constructors?

You should be able to use something similar to:

public T getObject<T>(T obj)
{
  return obj.newInstance();
}