An interface is not a class. Writing an interface is similar to writing a class, but they are two different concepts. A class describes the attributes and behaviors of an object. An interface contains behaviors that a class implements.
Unless the class that implements the interface is abstract, all the methods of the interface need to be defined in the class.
Declaring an interface:
While Java provides interfaces for you to use, you can also create your own.
An interface is declared with the interface keyword.
Syntax:
interface nameOfInterface{
//methods for interface here;
}
To use a interface in your class , append the keyword “implements” after your class name followed by the interface name
public class JavaInterfaceExample implements IntExample
Java Interface Example :
interface IntExample{
public void sayHello();
}
}
public class JavaInterfaceExample implements IntExample{
public void sayHello(){
System.out.println("Hello Visitor !");
}
public static void main(String args[]){
JavaInterfaceExample javaInterfaceExample = new JavaInterfaceExample();
javaInterfaceExample.sayHello();
}
}
Points to note:
Example:
interface RidableAnimal extends Animal, Vehicle
Class vs Interface:
An interface is similar to a class in the following ways:
However, an interface is different from a class in several ways, including:
Rules for Implementing Interfaces:
When overriding methods defined in interfaces there are several rules to be followed:
When implementation interfaces there are several rules:
Extending Interfaces:
An interface can extend another interface, similarly to the way that a class can extend another class. The extends keyword is used to extend an interface, and the child interface inherits the methods of the parent interface.
//Filename: Sports.java
public interface Sports
{
public void setHomeTeam(String name);
public void setVisitingTeam(String name);
}
//Filename: Football.java
public interface Football extends Sports
{
public void homeTeamScored(int points);
public void visitingTeamScored(int points);
public void endOfQuarter(int quarter);
}
//Filename: Hockey.java
public interface Hockey extends Sports
{
public void homeGoalScored();
public void visitingGoalScored();
public void endOfPeriod(int period);
public void overtimePeriod(int ot);
}
The Hockey interface has four methods, but it inherits two from Sports; thus, a class that implements Hockey needs to implement all six methods. Similarly, a class that implements Football needs to define the three methods from Football and the two methods from Sports.
Extending Multiple Interfaces:
A Java class can only extend one parent class. Multiple inheritance is not allowed. Interfaces are not classes, however, and an interface can extend more than one parent interface.
The extends keyword is used once, and the parent interfaces are declared in a comma-separated list.
For example, if the Hockey interface extended both Sports and Event, it would be declared as:
public interface Hockey extends Sports, Event
Tagging Interfaces:
The most common use of extending interfaces occurs when the parent interface does not contain any methods. For example, the MouseListener interface in the java.awt.event package extended java.util.EventListener, which is defined as:
package java.util;
public interface EventListener
{}
An interface with no methods in it is referred to as a tagging interface. There are two basic design purposes of tagging interfaces:
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