访问在重写的方法java中声明的方法

Question

I am having a bit of trouble with accessing an object declared in the main from a different class:

public static void main(String[]args)
{ 
  Knight knight=new Knight();
  Room2 room2=new Room2()
}

The problem is that I can't pass the object as an argument in this particular method as its an actionListener overridden method so something like this Accessing objects of other classes wouldn't work.

public void actionPerformed(ActionEvent e)
{
    if(e.getSource()==attack)
    {
        knight.getHealth();
    }
}

I can't pass anything extra after the ActionEvent e argument so I wanted to ask is this possible for the knight object to be recognized in this class or do I have to do something completely different? thanks

Edit: The main method is simply creating character objects like knight which is a concrete class:

public class Room2 extends JFrame implements ActionListener{

    private JButton attack;
    private JButton defend;
    //private JLabel item1read;

    CardLayout cl=new CardLayout();
    GridBagConstraints gb=new GridBagConstraints();
    JPanel panel =new JPanel();

    public Room2()
    {
        //******************************
        battlePanel.setLayout(new GridBagLayout());

        attack=new JButton("Attack");
        gb.gridx=1;
        gb.gridy=1;
        gb.insets=new Insets(10,10,10,10);
        attack.addActionListener(this);
        battlePanel.add(attack,gb);

        defend=new JButton("defend");
        gb.gridx=1;
        gb.gridy=2;
        battlePanel.add(defend,gb);
    }

    public void actionPerformed(ActionEvent e)
    {    
        if(e.getSource()==attack)
        {
             knight.getHealth();    
        }
    }
}

Answer 1

This line...

Knight knight=new Knight();

... only has scope within the main method.

Either you are going to have to instantiate a concrete object of your application and access the Knight via a getKnight() method in the actionPerformed handler.

public class TestClass {
    Knight knight;

    public static void main(String[] args) {
        TestClass testClass = new TestClass();
        testClass.run();
    }

    public Knight getKnight() {
        return this.knight;
    }

    public void run() {
        this.knight = new Knight();

        // Do other stuff, add event handler, etc. Then you can access via getKnight() method.
    }
}

Or you're going to have to define your Knight object as a static variable of the main application's class and access it statically from the actionPerformed handler eg

public static Knight knight;

This is less preferable, as it makes the Knight more visible to other classes and can easily be altered outside of the main class that contains it.

Answer 2

Based on your code, you will want to pass your Knight instance into the Room instance, perhaps via its constructor:

private Knight knight;

public Room2(final Knight knight) {

    this.knight = knight;

    battlePanel.setLayout(new GridBagLayout());
    attack=new JButton("Attack");
    gb.gridx=1;
    gb.gridy=1;
    gb.insets=new Insets(10,10,10,10);
    attack.addActionListener(this);
    battlePanel.add(attack,gb);
    defend=new JButton("defend");
    gb.gridx=1;
    gb.gridy=2;
    battlePanel.add(defend,gb);

    public void actionPerformed(ActionEvent e) {
        if(e.getSource()==attack){
            knight.getHealth();
        }
    }
}

And when creating it, pass it in:

Room room = new Room(knight);

eg,

public static void main(String[]args) { 
  Knight knight=new Knight();
  Room2 room2=new Room2(knight);
}

---

Better still, if the Room2 represents a physical room, and the knight an actual knight, then I would base my model on reality -- the knight isn't always inside of a room, and so I'd base my code on this reality. Perhaps give Room2 an enter(...) and exit(...) method pair, allowing the the GameManager class the ability to call these methods. The Room could also have a public List<Participants> listParticipants() or something similar type method that would list all knights, monsters or whatever that happen to be in that room. Then room behaviors could depend on its occupants.

Likewise you could give all your participants a location field as well as a setLocation(...) method with a getter method as well, so that all participant behaviors (including that of the knight) can change depending on their location.