Constructor getTypeParameters() method in Java with Examples

The getTypeParameters() method of a Constructor class is used to get an array of TypeVariable objects declared by this Constructor Object, in declaration order. Elements of array represent the type variables objects declared by Method. An array of length 0 is returned by this getTypeParameters(), if the Method Object generic declaration contains no type variables. 

Syntax:

public TypeVariable<Constructor<T>>[] getTypeParameters()

Parameters: This method does not accept any parameters. 

Return value: This method returns an array of TypeVariable objects that represent the type variables declared by this generic declaration. 

Exception: This method throws GenericSignatureFormatError if the generic signature of this generic declaration does not conform to the format specified in The Java™ Virtual Machine Specification. 

Below programs illustrate the getTypeParameters() method: 

Program 1:

Java

// Java program to demonstrate
// Constructor.getTypeParameters() method

import java.lang.reflect.Constructor;
import java.lang.reflect.TypeVariable;

public class GFG {

    public static void main(String... args)
        throws NoSuchMethodException
    {

        // Create Test class
        Class<Test> cls = Test.class;

        // Create Constructor Object
        Constructor[] constructors
            = cls.getConstructors();

        // get Type Parameters
        TypeVariable[] typeVariables
            = constructors[0].getTypeParameters();

        System.out.println("TypeVariables:"
                           + typeVariables);
    }
}
class Test<N extends Number> {
    public Test(N n) {}
}

Output:

TypeVariables:[Ljava.lang.reflect.TypeVariable;@15db9742

Program 2:

Java

// Java program to demonstrate
// Constructor.getTypeParameters() method

import java.lang.reflect.TypeVariable;

public class GFG {

    public static void main(String... args)
    {

        // get Type Parameters
        TypeVariable<Class<GFG_Demo> >[] typeParameters
            = GFG_Demo.class.getTypeParameters();

        // print result
        for (TypeVariable<Class<GFG_Demo> >
                 typeParameter : typeParameters) {
            System.out.println(typeParameter);
        }
    }

    private static class GFG_Demo<N, E> {
    }
}

Output:

N
E

References: https://docs.oracle.com/javase/10/docs/api/java/lang/reflect/Constructor.html#getTypeParameters()