Question

I am not sure if the title is accurate. I have several classes like Tv and I want to use all of them in only one class. Is it possible to call the methods in Tv in another class? If so, do I need to revise the constructor in class Tv? (TS is an interface).

class Tv implements TS{

    private String v;

    public Tv(String v){
            this.v = v;
    }

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

        public void volume(String v){
        ...
        }

}

public class TvSet{
    public static void main(String args[]){
        Tv t = new Tv("+");
    }
}

I have tried this:

public class RunTv {
    Remote r = new Remote("+");
    Tv t = new Tv("+");
    t.open();
}

The IDE reminds me “identifier expected after this token.” Should I modify Tv or RunTv?

Answer 1

The first problem is already answered by Owl and Roddy of the Frozen Pea, but to summarize: Yes you can call methods in another class as long as they are public and you have an instance of the class containing the method.

For your other problem with the “identifier expected...” error, you should change RunTv.

You cannot call t.open() outside a method block. If you changed it to something like this:

public class RunTv {
    public void openNewTv()
    {
       Remote r = new Remote("+");
       Tv t = new Tv("+");
       t.open();
    }
}

Then whenever you call the openNewTv method it will create a new instance of Remote and Tv and it will then call the open method in the Tv instance. To call openNewTv you could create an instance of RunTv in your main method like this:

public class TvSet{
    public static void main(String args[]){
        Tv t = new Tv("+");
        RunTv runTv = new RunTv();
        runTv.openNewTv();
    }
}

If you do not want to create a new instance every time you have to open a new Tv you could make the method static, which means it will not belong any instance, but rather the class itself (To understand these things better, you should read this)
You can make the method static like this:

public class RunTv {
    public static void openNewTv()
    {
       Remote r = new Remote("+");
       Tv t = new Tv("+");
       t.open();
    }
}

Now you can call openNewTv without having to create an instance of RunTv like this:

public class TvSet{
    public static void main(String args[]){
        Tv t = new Tv("+");
        runTv.openNewTv();
    }
}

Hope this helps. 🙂