java abstract class,concrete class and interface

what is the meaning of abstract class,concrete class and interface ?
1. In Java there is no multipliable inheritance like in C++ .But you can implement more thank one interface .
The interface methods are all abstract , this means contain no body ,and all properties are public static final (Means can't be changed later) . In interface you just say what is the class but don't say how to do it . Methods of interface are public and abstract by defaults and you don't need write the modifiers. interface can extend one or more interfaces .

Example

Code:


 interface shape 
{
         public abstract void   draw(); 


 } 
 

Here a class circle implements the shape interface.

Code:

class shape implements shape
{
          public void draw()
                        {
                          // Draw body 
                         }


}  

 

2. Abstract class can have implemented methods and others not , you can't have an abstract method in non abstract class. you have always to remember to that abstract methods end with semicolon . example

Code:


public abstract class Vehicle {
private String type;
public abstract void goUpHill(); // Abstract method
public String getType() { // Non-abstract method
return type;
}
}
public abstract class Car extends Vehicle {
public abstract void goUpHill(); // Still abstract
public void doCarThings() {
// special car code goes here
}
}
public class Mini extends Car {
public void goUpHill() {
// Mini-specific going uphill code
}
}