Interface
Interface in java is one of the way to achieve 100% abstraction in Java .
Interface in java is declared using keyword interface. It is also just like normal class. For interface also the .class file is going to be generated.
All methods inside interface are public by default
All variables declared inside interface is implicitly public final variable or constants.
interface Office
{
int employee;//Error because only final variables so they need to be initialised has donoted in below example. No other types are allowed inside interface
}
interface Office
{
int employee=100;
}
All methods declared inside Java Interfaces are implicitly public and abstract, even if you don't use public or abstract keyword
Cant create the Object of interface
In Java its legal for an interface to extend multiple interface. for example following code will run without any compilation error
interface Animal
{
public void eat();
public void walk();
}
interface Human
{
public void talk();
public void work();
}
interface Livingbeing extends Animal,Human // extend multiple interface
{
public void enjoyWithLover();
Whenever we implement interface we need to provide implementation to all the abstract methods of it, or else we need to make the inherited class also has abstract.
interface Office
{
void work();
public void enjoy();
}
abstract class Manager implements Office
{
//implementation is not give for work() and enjoy() so class should be abstract
}
Example:-
{
public void eat();
public void walk();
}
interface Human
{
public void talk();
public void work();
}
interface Livingbeing extends Animal,Human
{
public void enjoyWithLover();
}
public class Test implements Livingbeing
{
public void eat()
{
// TODO Auto-generated method stub
}
public void walk()
{
// TODO Auto-generated method stub
}
public void talk()
{
// TODO Auto-generated method stub
}
public void work()
{
// TODO Auto-generated method stub
}
public void enjoyWithLover()
{
// TODO Auto-generated method stub
}
}
The Interface reference can be give to its child class object. It behave same has the inheritance. Using the interface reference we cant accesses the child class members. But we can accesses the overrided methods.
Example:
{
public void eat();
public void walk();
}
class Cow implements Animal
{
public void eat()
{
System.out.println("Cow eat hullu");
}
public void walk()
{
System.out.println("Cow walk in four legs");
}
public void giveMilk()
{
System.out.println("Cow give white milk");
}
}
class Test1
{
public static void main(String[] args)
{
Animal a = new Cow();
a.eat();
a.walk();
a.giveMilk();//Error because parent reference cant accesses child members
}
}
Difference Between Abstract class and interface in java
| Abstract | Interface | |
| Multiple Inheritance | A class can inherit only one Abstract Class |
A class can implement multiple Interfaces |
| Concrete methods (Default Behavior) |
In abstract class you can provide default behavior of a method, so that even if child class does not provide its own behavior, you do have a default behavior to work with |
You cannot provide a default behavior in interfaces. Interfaces only allow you to provide signature of the method |
| Access Modifiers | You can provide access modifiers to methods in abstract classes (static , final, etc) |
You cannot provide access modifiers methods in Interfaces. |
| Methods and variables | The methods or variables can be declared with any accesses specifiers and modifiers. (Note : but abstract methods should not be static , final, private) |
All methods are public by default, all the variables are static final by default. |
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