Interface in java with example program ppt

Why not just use abstract classes? Java does not permit multiple inheritance from classes, but permits implementation of multiple interfaces. One class can implement many interfaces One interface can be implemented by many classes By providing the interface keyword, Java allows you to fully utilize the "one interface, multiple methods" aspect of polymorphism. Why an Interface?

Normally, in order for a method to be called from one class to another, both classes need to be present at compile time so the Java compiler can check to ensure that the method signatures are compatible. In a system like this, functionality gets pushed up higher and higher in the class hierarchy so that the mechanisms will be available to more and more subclasses. Interfaces are designed to avoid this problem.

Interfaces are designed to support dynamic method resolution at run time. They disconnect the definition of a method or set of methods from the inheritance hierarchy.

Since interfaces are in a different hierarchy from classes, it is possible for classes that are unrelated in terms of the class hierarchy to implement the same interface. This is where the real power of interfaces is realized. Creating an Interface File InterfaceName.

File ClassName. Creating a Multiple Interface If a class implements a multiple interfaces, it should override all the abstract methods declared in all the interfaces. Access via interface reference You can declare variables as object references that use an interface rather than a class type. Any instance of any class that implements the declared interface can be stored in such a variable. Example: Comparable circle; When you call a method through one of these references, the correct version will be called based on the actual instance of the interface being referred to.

Using Interface This is one of the key features of interfaces. The method to be executed is looked up dynamically at run time, allowing classes to be created later than the code which calls methods on them. The calling code can dispatch through an interface without having to know anything about the "callee. Interfaces vs. An abstract class must contain at least one abstract method or inherit from another abstract method.

Abstract Classes, cont. Now, if any class implements Polygon , it should provide implementations for all the abstract methods of both Line and Polygon. Note : All the methods inside an interface are implicitly public and all fields are implicitly public static final.

With the release of Java 8, we can now add methods with implementation inside an interface. These methods are called default methods. To declare default methods inside interfaces, we use the default keyword. We can add the method in our interface easily without implementation.

However, that's not the end of the story. All our classes that implement that interface must provide an implementation for the method. If a large number of classes were implementing this interface, we need to track all these classes and make changes to them. This is not only tedious but error-prone as well. To resolve this, Java introduced default methods. Default methods are inherited like ordinary methods.

It has a default method getSides and an abstract method getArea. Here, we have created two classes Rectangle and Square that implement Polygon. The Rectangle class provides the implementation of the getArea method and overrides the getSides method. However, the Square class only provides the implementation of the getArea method. Now, while calling the getSides method using the Rectangle object, the overridden method is called.

However, in the case of the Square object, the default method is called. Similar to a class, we can access static methods of an interface using its references. Note : With the release of Java 9, private methods are also supported in interfaces. Strings in Java.

OOPS in Java. Constructors in Java. Interfaces in Java. Keywords in Java. Exception Handling in Java. Collection Framework. Multi-threading in Java. Table of Contents. Improve Article. Save Article. Like Article. Attention reader! Get hold of all the important Java Foundation and Collections concepts with the Fundamentals of Java and Java Collections Course at a student-friendly price and become industry ready.

Previous Encapsulation in Java. Next Nested Interface in Java. The body of the interface method is provided by the "implement" class:. Try it Yourself ». However, it can be achieved with interfaces, because the class can implement multiple interfaces.

Note: To implement multiple interfaces, separate them with a comma see example below.