Destroying objects in Java

Question

I have a general idea of how the Garbage Collector works in Java, but my reasoning for destroying an object is not because I care about freeing up memory, but because of functio

Answer 1

As an extension to what @pstanton said, keep collections of owned objects. Here's an elaborate way, which is useful for preventing mistaken code from corrupting your state.

public abstract class Possession {
  private Object _key = null;

  public synchronized Object acquire() {
    if (_key != null) { throw new IllegalStateException(); }
    _key = new Object();
  }

  public synchronized void release(Object key) {
    if (_key != key) { throw new IllegalStateException(); }
    _key = null;
  }
}

public class Possessions implements Iterable {
  private final Map _possessions = new IdentityHashMap<...>();

  public synchronized void add(Possession p) {
    if (!_possessions.containsKey(p)) {
      _possessions.put(p, p.acquire());
    }
  }

  public synchronized void remove(Possession p) {
    Object key = _possessions.remove(p);
    if (key != null) {
      p.release(key);
    }
  }

  public Iterator iterator() {
    return Collections.unmodifiableSet(_possessions.keySet()).iterator();
  }
}

public class Money extends Possession { ... }

public class Person {
  private final Possessions _possessions = new Possessions();

  public void add(Money money) {
    _possessions.add(money);
  }
}