First of all lets explore it non-technically !
What does 'abstract' mean ?
well abstract is something on your mind ! you dream of a house, its abstract. You build a house, its concrete.
Now its techies' dinner time !
Please declare abstract before you present your dream.
abstract class MyDreamHouse{
}
now you want workers to build ? You are given workers ! Now tell them methods !
wait ! you dont know how to implement them or want others to do it for you ? leave them abstract and put a semicolon(;) after the prototype !
abstract class MyDreamHouse{
abstract void makeLift(Object o);
}
Hmm ! you know something ! you can paint your gate ! :P ok do it yourself ! ofcourse you cant declare it abstract ! seems legit !
abstract class MyDreamHouse{
abstract void makeLift(Object o);
void paintGate(Object o){
//your painting code goes here
}
//rest of the works are straight forward; you declare abstract methods, you define concrete methods
}
Let your friend extend your dream !
class HulkHouse extends MyDreamHouse{
@Override
void makeLift(Object o) {
//hulk builds lift
}
}
He might also doesn't know how to makeLift ! so he dont dare to implement it ! Poor Hulk ! he must declare his class abstract too !
abstract class HulkHouse extends MyDreamHouse{
void buildGarrage(Object o){
}
abstract void attachDoors(Object o);
}
almost done !
we know there is a restriction on implementing interfaces. We must implement all the methods declared in the interface ! okay ! if we dont want to ? We get permissions paying respect to our friend 'abstract' ! just put him before the class declaration ! or get error ! :P
abstract class BlaBla implements Runnable{
}
ok you might expect your son to implement the method u must implement !
class SonBlaBla extends BlaBla{
public void run() {
}
}
or you should do as below to avoid error
class BlaBla implements Runnable{
public void run() {
}
}
One very important thing ! you cannot instantiate abstract classes !
like : MyDreamHouse myhouse1=new MyDreamHouse(); //compilation error
Sad thing ! Dont cry ! Dont panic ! You still can use ur class type in main or other relevant places.
Let me show how !
A complete code listing:
abstract class MyDreamHouse{
abstract void makeLift(Object o);
void paintGate(Object o){
//your painting code goes here
}
}
abstract class HulkHouse extends MyDreamHouse{
void buildGarrage(Object o){
}
abstract void attachDoors(Object o);
}
class RealHouse extends HulkHouse{
@Override
void attachDoors(Object o) {
}
@Override
void makeLift(Object o) {
}
}
class abstractTester{
public static void main(String[] args){
MyDreamHouse myHouse1; // its ok ! coz no instances is created!
HulkHouse hulkHouse1; // its ok ! coz no instances is created!
RealHouse realHouse1=new RealHouse();
RealHouse realHouse2=new RealHouse();
myHouse1=realHouse1;
myHouse1.makeLift("Lift 1"); //calls its child realHouse1's method
hulkHouse1=realHouse2;
hulkHouse1.makeLift("Lift 2");
}
}
code Link : http://pastebin.com/LXByEK7u
