final/src/Middleware.java

import com.sun.jdi.request.DuplicateRequestException;

import java.awt.event.KeyEvent;
import java.io.Serializable;
import java.util.ArrayList;

public class Middleware implements Serializable {

    public static ArrayList<Integer> allOldCode = new ArrayList<Integer>();
    public static ArrayList<Integer> allNewCode = new ArrayList<Integer>();
    public final int oldCode;
    public final int newCode;
    public boolean isDestroyed = false;

    Middleware(int oldCode, int newCode) {
        // if (!canCreate(oldCode, newCode)) {
            // TODO: replace with more appropriate exception
        //     throw new DuplicateRequestException();
        // }
        allOldCode.add(oldCode);
        allNewCode.add(newCode);
        this.oldCode = oldCode;
        this.newCode = newCode;
    }

    public boolean canIntercept(KeyEvent e) {
        return e.getKeyCode() == newCode && !isDestroyed;
    }

    public KeyEvent interceptKey(KeyEvent e) {
        e.setKeyCode(oldCode);
        return e;
    }

    public void destroy() {
        allOldCode.remove(oldCode);
        allNewCode.remove(newCode);
        isDestroyed = true;
    }

    public static boolean canCreate(int oldCode, int newCode) {
        return (!allOldCode.contains(oldCode) && !allNewCode.contains(newCode));
    }

    @Override
    public boolean equals(Object o) {
        try {
            Middleware m = (Middleware)o;
            // duck typing equals check
            // if it has the same oldCode, assume it is the same; this is because oldCodes should be unique
            // also makes some corner cases easier
            return this.oldCode == m.oldCode || this.newCode == m.newCode;
        } catch (ClassCastException e) {
            return false;
        }
    }
}