What is the use of extends and super in generics?
super is a lower bound, and extends is an upper bound. According to http://download.oracle.com/javase/tutorial/extra/generics/morefun.html : The solution is to use a form of bounded wildcard we haven’t seen yet: wildcards with a lower bound.
What is difference between extends and super in generics?
Wildcards in Generics A question mark, or wildcard, is used in generics to represent an unknown type. extends Number> represents a list of Number or its sub-types such as Integer and Double. Lower Bounded Wildcards: List represents a list of Integer or its super-types Number and Object.
What is difference between extends and super?
<T extends Parent> accepts either Parent or Child while accepts either Parent or Grandparent. Use List< T super Suit> whenever you are going to write into the list. Use List< T extends Suit> whenever you are going to read from a list.
Why do producers extend consumer super?
super Thing guarantees. I’m always trying to think about it this way: A producer is allowed to produce something more specific, hence extends, a consumer is allowed to accept something more general, hence super. Another way to remember the producer/consumer distinction is to think of a method signature.
What is Super E in Java?
super E> , it means “something in the super direction” as opposed to something in the extends direction. Example: Object is in the super direction of Number (since it is a super class) and Integer is in the extends direction (since it extends Number ).
What are generic classes in Java?
Generics mean parameterized types. The idea is to allow type (Integer, String, … etc, and user-defined types) to be a parameter to methods, classes, and interfaces. Using Generics, it is possible to create classes that work with different data types.
What does super () Do Java?
The super() in Java is a reference variable that is used to refer parent class constructors. super can be used to call parent class’ variables and methods. super() can be used to call parent class’ constructors only.
Can we use this () and super () in a constructor?
both this() and super() can not be used together in constructor. this() is used to call default constructor of same class.it should be first statement inside constructor. super() is used to call default constructor of base class.it should be first statement inside constructor.
What is Super T in Java?
super T denotes an unknown type that is a supertype of T (or T itself; remember that the supertype relation is reflexive). It is the dual of the bounded wildcards we’ve been using, where we use ? extends T to denote an unknown type that is a subtype of T .
What does Super E mean?
something in the super direction
super E> , it means “something in the super direction” as opposed to something in the extends direction. Example: Object is in the super direction of Number (since it is a super class) and Integer is in the extends direction (since it extends Number ).
What does E mean in Java?
Here denotes the type parameter of Node class . The type parameter defines that it can refer to any type (like String, Integer, Employee etc.). Java generics have type parameter naming conventions like following: T – Type. E – Element.
What are the advantages of generics in Java?
Code that uses generics has many benefits over non-generic code: Stronger type checks at compile time. A Java compiler applies strong type checking to generic code and issues errors if the code violates type safety. Fixing compile-time errors is easier than fixing runtime errors, which can be difficult to find.
What is generic method in Java?
Java Generic methods and generic classes enable programmers to specify , with a single method declaration, a set of related methods, or with a single class declaration, a set of related types, respectively. Generics also provide compile-time type safety that allows programmers to catch invalid types at compile time.
What is generic class in Java?
A generic class in Java is a class that can operate on a specific type specified by the programmer at compile time. To accomplish that, the class definition uses type parameters that act as variables that represent types (such as int or String). To create a generic class, you list the type parameter after the class name in angle brackets.
What is a Java superclass?
What is a Java superclass. A Java superclass is a class which gives a method or methods to a Java subclass. A Java class may be either a subclass, a superclass, both, or neither! The Cat class in the following example is the subclass and the Animal class is the superclass.
