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This noncompliant code example (based on \[[Goetz 04|AA. Java References#Goetz 04]\]) shows a container, {{MutableHolder}}. In {{MutableHolder}}, the instance field {{value}} can be updated to reference a new value using the {{setValue()}} method which makes its existence long-term. This reducesslows the efficiency of the down garbage collectorcollection.

public class MutableHolder {
  private Hashtable<Integer, String> value; // not final
  public Object getValue() { return value; }
  public void setValue(Hashtable<Integer, String> ht) { value = (Hashtable<Integer, String>)ht; }
}

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Array based data structures such as ArrayLists are an exception as the programmer has to explicitly set only a few of the array elements to null to indicate their demise.

Long-lived objects containing short-lived objects

Always remove short-lived objects from the long-lived container objects when the task is over. For example, objects attached to a java.nio.channels.SelectionKey object must be removed when they are no longer needed. Doing so reduces the possibility of memory leaks.

Do Not Explicitly Invoke the Garbage Collector

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