What is an interface in Java ?
Interfaces define a contract that an implementing class must agree to.
If a class implements an interface, it must provide implementation of all the methods or define itself as abstract.
Interfaces provide an way of using multiple inheritance in java since a class can extend only one other class, but it may implement any number of interfaces.
Here are some of the rules regarding Interfaces :
– A class can extend only one class, but it can implement multiple interfaces.
– Methods in interfaces are implicitly abstract and their scope is public. Since they are abstract and need to be overridden, they can not be final.
– Interface methods can not be static
– Interface variables are public, static and final. That means variables in interfaces are basically constants.
– Interface can extend one or more interfaces. Interface cannot extend a class and it can not implement a class/interface as well.
– Interfaces are implicitly abstract. So, although its redundant, you can add abstract to the interface declaration as well
– A class implementing an interface can itself be abstract.
Example
Here is a sample interface that provides signature for a printText() method.
package com.javatutorial;
public interface TestInterface {
public void printText(String name);
}
Now any class implementing this interface has to provide implementation for the printText() method.
We can implement it as follows :
package com.javatutorial;
public class Hello implements TestInterface {
public static void main(String[] args) {
Hello h =new Hello();
h.printText("user");
}
@Override
public void printText(String name) {
System.out.println("Hello "+ name);
}
}
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