如何在实例类中的实例上调用方法？

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.

Answer 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

Answer 2

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!

Answer 3

this should work

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