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Java – Tips

Interface:
============

// when we say interface we dont use function brackets;
public interface MainCar {

//
int shamun(int a);

}

// when we say “Implements” we add function brackets
public class A implements MainCar {

int shamun(int a){
// more…..
}
}

public interface groupInterface extends interface1,interface2 {
double E = 2.33;
void newMore(int i);
}

Inheritance:
============
When you want to create a new class and there is already a class that includes
some of the code that you want, you can derive your new class from the existing
class. In doing this, you can resuse the fields and methods of the existing
class without having to write
(and debug !) them yourself.

An Example of Inheritance
Here is the sample code for a possible implementation of a Bicycle class that was presented in the Classes and Objects lesson:

public class Bicycle {

// the Bicycle class has three fields
public int cadence;
public int gear;
public int speed;

// the Bicycle class has one constructor
public Bicycle(int startCadence, int startSpeed, int startGear) {
gear = startGear;
cadence = startCadence;
speed = startSpeed;
}

// the Bicycle class has four methods
public void setCadence(int newValue) {
cadence = newValue;
}

public void setGear(int newValue) {
gear = newValue;
}

public void applyBrake(int decrement) {
speed -= decrement;
}

public void speedUp(int increment) {
speed += increment;
}

}

A class declaration for a MountainBike class that is a subclass of Bicycle might look like this:

public class MountainBike extends Bicycle {

// the MountainBike subclass adds one field
public int seatHeight;

// the MountainBike subclass has one constructor
public MountainBike(int startHeight, int startCadence, int startSpeed, int startGear) {
super(startCadence, startSpeed, startGear);
seatHeight = startHeight;
}

// the MountainBike subclass adds one method
public void setHeight(int newValue) {
seatHeight = newValue;
}

}

MountainBike inherits all the fields and methods of Bicycle and adds the field seatHeight and a method to set it. Except for the constructor, it is as if you had written a new MountainBike class entirely from scratch, with four fields and five methods. However, you didn’t have to do all the work. This would be especially valuable if the methods in the Bicycle class were complex and had taken substantial time to debug.

Polymorphism:

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