在抽象类Java中的类中声明接口并实现

Question

I am doing an exercise, the book is not helping me grasp the concept, neither are the online resources. This may seem really silly but I don't know what I'm missing!!! I am quite new to Java and have had a look at other examples on stack but to no avail :s I need to declare 3 interfaces. Each interface needs to declare a method with the same name as its interface. Then the abstract class is extended by 3 classes which implement the aforementioned interfaces.Each class needs to be instantiated. If anyone could explain the procedure to this I would be eternally grateful.

interface antiLockBrakes{
    public void antiLockBrakes();
}

interface cruiseControl{
    public void cruiseControl();
}

interface powerSteering{
    public void powerSteering();
}

public abstract class Auto{
    abstract class Model1 extends Auto implements antiLockBrakes{
        public abstract void antiLockBrakes();
        Model1 mod1 = new Model1();
        mod1.antiLockBrakes();
    }

    public static void main(String[] args){
    }   
}

Answer 1

this is your question: someone to explain how exactly to declare and interface and then have it implemented in the abstract class right??

Here's the answer for it.

See lets consider I have an interface

interface someInterface{
    public void someMethod();
}

Now to implement the someInterface in abstract class

public abstract class SomeClass implements someInterface{
    public void someMethod(){
              System.out.println("Inside someMethod");
    }
    public abstract myMethod();
}

See in the class SomeClass we have implemented interface by giving definition to method someMethod() and since we want this SomeClass to be a abstract class we have defined one abstract method myMethod() for it.

Now any class which extends from SomeClass will also implement interface someInterface implicitly (because SomeClass has implemented it) and if it want its own definition for someMethod() it can override it. But if a child class wants to be a concrete class ( a class in which all its method will have implementation) then it has to provide implementation for abstract method myMethod().

HTH:)

Answer 2

this is what I like to use to see the difference between abstract classes and interface classes

interface class

//I say all motor vehicles should look like that :
interface MotorVehicle {


    void run();

    int getFuel();
}

// my team mate complies and write vehicle looking that way
class Car implements MotorVehicle {

    int fuel;

    public void run() {
        System.out.println("Wrroooooooom");
    }

    public int getFuel() {
        return this.fuel;
    }
}

abstract class

// I say all motor vehicles should look like that :
abstract class MotorVehicle2 {

    int fuel;

    // they ALL have fuel, so why let others implement that ?
    // let's make it for everybody
    int getFuel() {
        return this.fuel;
    }

    // that can be very different, force them to provide their
    // implementation
    abstract void run();

}

// my team mate complies and write vehicle looking that way
class Car2 extends MotorVehicle2 {
    void run() {
        System.out.println("Wrroooooooom");
    }
}