Application doesn't display output

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Java application doesn't display output

I am learning the basics of Java development so that I can get into Android development. In this very simple application I'm running into some problems. It's supposed to give me an output of the cars speed, gears, rpm and so forth. I can compile the application no problem but when I go to run it it doesn't display the output. What could the problem be? Here's the code:

package car1;

public class Main {



    public static void main(String[] args) {

            class HondaCivic implements car1 {

                int speed = 0;
                int rpm = 0;
                int gear = 1;

                void speedUp(int Increment) {
                    speed = speed + Increment;}

                void applyBrakes(int Decrement) {
                    speed = speed - Decrement;}

                void changeRpm(int NewValue) {
                    rpm = NewValue;}

                void changeGear(int NewValue) {
                    gear = NewValue;}

                void printStates() {
                    System.out.println("speed:"+speed+" rpm:"+rpm+" gear:"+gear);
                }
            }


            class Car1{
                public void main(String[] args) {
                    // Two different Cars
                    HondaCivic car1 = new HondaCivic();
                    HondaCivic car2 = new HondaCivic();
                    // Methods for cars
                    car1.speedUp(30);
                    car1.changeGear(3);
                    car1.changeRpm(3000);
                    car1.applyBrakes(15);
                    car1.printStates();

                    car2.speedUp(30);
                    car2.changeGear(3);
                    car2.changeRpm(2000);
                    car2.applyBrakes(15);
                    car2.speedUp(5);
                    car2.changeGear(1);
                    car2.printStates();
                }

            }
        }
    }
}

Answer 1

You can't compile.

Your HondaCivic class implements car1 which doesn't exists. It could be Car1 but Car1 is a class and should be extended.

Plus having two classes declared in your main method isn't really a good idea. You can't access them from outside the method.

And in the end you have two main(String...) method. I suppose that it's the Main.main(String...) that is called. This method does nothing except declaring two classes.

Answer 2

HondaCivic in this case should not be a class, it should be an instance of a Car or any subclass of car. The Car Class should have the make, year, model etc of the car. Now if there is different behavior for say a HondaCivic, you would add any information that would help define this, for example max_speed, or like you did the state of the cars systems such as current_speed, brakes, gear, etc.

Now if you want to go further in the design you could create a class for the different parts of a car and you start seeing how this fits nicely in object oriented design.

Answer 3

This is what your classes should look like

HondaCivic.java

public class HondaCivic  {

                int speed = 0;
                int rpm = 0;
                int gear = 1;

                void speedUp(int Increment) {
                    speed = speed + Increment;}

                void applyBrakes(int Decrement) {
                    speed = speed - Decrement;}

                void changeRpm(int NewValue) {
                    rpm = NewValue;}

                void changeGear(int NewValue) {
                    gear = NewValue;}

                void printStates() {
                    System.out.println("speed:"+speed+" rpm:"+rpm+" gear:"+gear);
                }
            }

Main.java

public class Main {

    public static void main(String[] args) {


    car1 = new HondaCivic();
    car2 = new HondaCivic();
    car1.speedUp(30);
    car1.changeGear(3);
    car1.changeRpm(3000);
    car1.applyBrakes(15);
    car1.printStates();

    car2.speedUp(30);
    car2.changeGear(3);
    car2.changeRpm(2000);
    car2.applyBrakes(15);
    car2.speedUp(5);
    car2.changeGear(1);
    car2.printStates();

     }
}

Answer 4

I don't know, but I think you could try using the Log to test your output

Just replace

System.out.println("speed:"+speed+" rpm:"+rpm+" gear:"+gear);

by

Log.i("OUTPUT", "speed:"+speed+" rpm:"+rpm+" gear:"+gear);

And look at the LogCat window

That is, if you are using Eclipse.

Answer 5

Your Main.main method doesn't contain any actual executable code. All it has is an embedded class definition, HondaCivic. It looks like your intent is that the code inside the Car1.main method is what should be inside the Main.main method -- that looks like what you really want to run. There's also no apparent reason for HondaCivic to be an embedded class. Clean that up and you basically have what Falmarri suggests.