variables in inteface

[Anjali Vaidya]

hi all!
actually i created a Vehicle interface which has methods engine(),body() and wheels(). Car class and Bike class implement this.
I want to create a variable called color and wheel in Vehicle so that every class which inherits it has these. But unfortunately, I cannot make it. Can anybody please help me in making variables which are used by all the inheriting classes of Vehicle?
Thanks in advance

[Piyush Joshi]

Anjali Vaidya wrote:But unfortunately, I cannot make it.

Can you show what have you tried?
and be aware that any field you declare in an Interface is implicitly public,static and final.

[Pramod P Deore]

import java.awt.Color;
interface Vehicle
{
	public static final Color color = Color.RED;
	
}

[Stephan van Hulst]

You can't, unless they are constants (static and final). Variables are implementation details, so they shouldn't be part of an interface.

Instead, what you can do is create an abstract class AbstractVehicle that implements Vehicle, and give that class the color variable (which should be private) and give it getter and/or setter methods to view or change the vehicles color. These methods are then inherited by Car and Bike, which both extend AbstractVehicle.

[Anjali Vaidya]

interface Vehicle
{
 int wheel;
 String colour;

 public void body();
 public void engine();
 public void wheels();
}

public class Caller
{
 public static void main(String[] args)
  {
   Car mycar=new Car();
   mycar.body();
   mycar.wheels();

   Car merc=new Mercedes();
   merc.body();

   Vehicle bi=new Bike();
   bi.body();
   bi.wheels();
  }
}

class Car implements Vehicle
{
 public void body()
 {
  System.out.println("this is the body of a car");
 }
 public void engine() { }
 public void wheels()
 {
  wheel=4;
  System.out.println("car has "+wheel+" wheels");
 }
}

class Mercedes extends Car //implements Vehicle
{
 public void body()
 {
  colour=black;
  System.out.println("you get only "+colour+" colour");
 }
}

class Bike implements Vehicle
{
 public void body()
 {
  System.out.println("this is a bike");
 }
 public void engine() { }
 public void wheels()
 {
  wheel=2;
  System.out.println("bike has "+wheel+" wheels");
 }
}

[Piyush Joshi]

interface Vehicle
{
 int wheel;
 String colour;

So now you see wheel and colour are implicitly constants so it is
pubilc static final int wheel;
public static final String colour;
So whatever you were trying can not be done this way.

But your requirement can be solved by following what Stephan has explained.