How can I call a method on an instance within the instance class?

Question

    public class Agent {
        private Space _location;
        private String _name;
        public void setLocation(Space space){
            _location = space;
        }
        public void usePortal(){
            if(_location.getPortal() != null){
            Portal.transport(Agent.this);
            }
        }
    }

java.lang.Error: Unresolved compilation problem: Cannot make a static reference to the non-static method transport(Agent) from the type Portal

Above is the error it gives me. I have a public class Space with a member variable of type Portal and a getPortal() getter. which looks like:

    public class Space {
        private String _name;
        private String _description;
        private Portal _portal;
        public Portal getPortal(){
            return _portal;
        }
    }

In my public Portal class, I have a transport method with an Agent parameter:

    public class Portal {
        private String _name;
        private String _direction;
        private Space _destination;
        public Space getDestination(){
            return _destination;
        }
        public void transport(Agent str){
            str.setLocation(getDestination());
        }
    }

My main problem is having the usePortal() method to work, the Space and Portal classes are fully functional. I don't know how I would call the method on an instance of Agent within the Agent class.

I don't understand your title. You're calling the instance method `transport` from the instance class `Agent`. Just make an instance of `Portal` and then call `portalInstance.transport(this);`? — Michael Yaworski, Sep 26 '14 at 18:53

Ajay George · Answer 1 · 2014-09-26T19:06:56.737

1

java.lang.Error: Unresolved compilation problem: Cannot make a static reference to the non-static method transport(Agent) from the type Portal

This is because transport method is an instance method and not static.

Either create an instance of Portal and then use that or make the transport method static

Portal portal = new Portal();
portal.transport(this);

or

public static void transport (Agent str)

I don't know how I would call the method on an instance of Agent within the Agent class.

Instead of Agent.this use just this

edited Sep 26 '14 at 19:06

answered Sep 26 '14 at 18:53

Ajay George

11,759
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Nice assumption skipping static method usage !! – Wundwin Born Sep 26 '14 at 18:55
@WundwinBorn added static method usage issue as well – Ajay George Sep 26 '14 at 19:01
Good explanation and +1 back !! Anyway should post code along with ! – Wundwin Born Sep 26 '14 at 19:04

proulxs · Answer 2 · 2014-09-26T19:13:27.453

1

You can't call other class methods without initializing an object reference. Unless it is declared static.

For example:

Portal portal = new Portal();
portal.transport(this);

Note that this is a reference to the current object, in this case, Agent.

Do some more research online to see how java objects work and also research static and non-static contexts. Tons of examples!

edited Sep 26 '14 at 19:13

answered Sep 26 '14 at 18:54

proulxs

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2
13

You should explain `this` keyword too !! – Wundwin Born Sep 26 '14 at 18:57

score 0 · Answer 3 · answered Sep 26 '14 at 19:11

0

this should work

public void usePortal(){
    if(_location.getPortal() != null){
    _location.getPortal().transport(this);
    }
}

answered Sep 26 '14 at 19:11

Anshul

159
1
10

How can I call a method on an instance within the instance class?

3 Answers3