Test Code
Here is some test code that demonstrates that I'm not talking nonsense. I invite you to use this code to test the SoftHashMap yourself.

Soft and weak references are quite difficult to experiment with, because there is a lot of freedom left to the writers of the JVM about how they can implement them. I wish the implementation would hold back longer before removing these references; that the JVM would wait until it is really running low on memory before clearing them, but I am not the one who wrote the JVM.

//: SoftHashMapTest.java
import java.lang.ref.*;
import java.util.*;

public class SoftHashMapTest {
  private static void print(Map map) {
    System.out.println("One=" + map.get("One"));
    System.out.println("Two=" + map.get("Two"));
    System.out.println("Three=" + map.get("Three"));
    System.out.println("Four=" + map.get("Four"));
    System.out.println("Five=" + map.get("Five"));
  }
  private static void testMap(Map map) {
    System.out.println("Testing " + map.getClass());
    map.put("One", new Integer(1));
    map.put("Two", new Integer(2));
    map.put("Three", new Integer(3));
    map.put("Four", new Integer(4));
    map.put("Five", new Integer(5));
    print(map);
    byte[] block = new byte[10*1024*1024]; // 10 MB
    print(map);
  }
  public static void main(String[] args) {
    testMap(new HashMap());
    testMap(new SoftHashMap(2));
  }
}


Many thanks to Sydney Redelinghuys for his input and corrections in this article. 



Dr. Heinz Kabutz owns Maximum Solutions, a Cape Town-based consulting firm that specializes in Java technology. He spends the majority of his time programming Java OO applications and also advises companies who wish to embrace Java as a technology. He has been a lead programmer in one of the first big Java developments in South Africa, now consisting of almost 600,000 lines of Java code. Heinz, who completed his doctorate in computer science at the University of Cape Town, South Africa, in 1996, has been programming in Java since 1997. He can be reached at h.kabutz@computer.org. Editor's note: This article first appeared Dr. Kabutz's  "The Java(tm) Specialists' Newsletter"; to subscribe, send an email to join-thejavaspecialists@burst.sparklist.com.

 

 

 

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                	The SoftHashMap Itself