A type argument must be passed to the type parameter of a base class. You can do so while extending the base class or while instantiating the derived class.
Examples :
1)
package com.gns.generics;
class Parcel<T> {
}
class GenericParcel<T> extends Parcel<T> {
}
public class Generic3 {
public static void main(String[] args) {
Parcel<String> parcel = new GenericParcel<String>();
// Parcel<String> parcel1 = new Parcel<Integer>(); won't compile
// Parcel<String> parcel1 = new Parcel<Object>(); wont't compile
}
}
2)
3)
package com.gns.generics;
class Parcel<T> {
}
class GenericParcel<X,T> extends Parcel<T> {
}
public class Generic3 {
public static void main(String[] args) {
Parcel<String> parcel = new GenericParcel<Integer,String>();
// Parcel<String> parcel1 = new Parcel<Integer>();
// Parcel<String> parcel1 = new Parcel<Object>();
}
}
4)
package com.gns.generics;
class Book{
}
class Parcel<T> {
}
class GenericParcel<X> extends Parcel<Book> {
}
public class Generic3 {
public static void main(String[] args) {
Parcel<Book> parcel = new GenericParcel<Integer>();
// Parcel<String> parcel1 = new Parcel<Integer>();
// Parcel<String> parcel1 = new Parcel<Object>();
}
}
5)
package com.gns.generics;
class Parcel<T> {
}
class GenericParcel<X> extends Parcel<String> {
}
public class Generic3 {
public static void main(String[] args) {
Parcel<String> parcel = new GenericParcel<Integer>();
}
}
NON-GENERIC CLASS EXTENDING A GENERIC CLASS
You can extend a generic base class to define a nongeneric base class. To do so, the derived class doesn’t define any type parameters but passes arguments to all type parameters of its generic base class. For example
package com.gs.corejava.generics;
class Phone{
}
class Parcel<T>{
}
class NonGenericPhoneParcel extends Parcel<Phone> {
}
public class Generic4 {
}
In the preceding example, NonGenericPhoneParcel is a nongeneric class that passes argument Phone to its base class Parcel.
You can’t pass type arguments to a nongeneric class.
