Use of getReturnType() of Java's reflection to create a new object of that type

Question

I am wondering if I can use the returned type of java's reflection method getReturnType() to create Objects of that type.

I have a method which returns a String, assume that we don't know that at run-time, so I call the getReturnType() to determine what type of Objects the method returns:

Method myMethod = Book.class.getDeclaredMethod("printName");
Type myType = myMethod.getReturnType();

I am wondering if it is possible to use that myType to create new Objects or how can I do that? I tried mytype something = new mytype(); but it is wrong.

Answer 1

First, the Method#getReturnType() is declared as such

 Class<?> java.lang.reflect.Method.getReturnType()

and the javadoc states that it

Returns a Class object that represents the formal return type of the method represented by this Method object.

The Class class provides a newInstance() method which can use the no argument constructor to create an instance or you can use the Class#getDeclaredConstructors() method to get a list of Constructor instances and use their newInstance(Object...) method to create an instance of the class represented.

You won't be able to create a variable of that type since the type is unknown at compile time.

Answer 2

Since the type itself is dynamic you can't declare a variable of that type, this because a declaration is a compile time feature.

Given that, you can istantiate an object of the returned type:

try {
  Method myMethod = Book.class.getDeclaredMethod("printName");
  Class<?> type = myMethod.getReturnType();
  Object instance = type.newInstance();
} 
catch (...) {
}

The problem is that you can't know the type variable of getReturnType() returned Class , you just know that this is a Class<?> so there's no way to know statically the type of the instance generated by type.newInstance() , hence you store it inside an Object .