Java Tutorial/Reflection/SoftReference
A soft reference holds onto its referent until memory becomes low.
<source lang="java">
import java.lang.ref.SoftReference; public class Main {
public static void main(String[] argv) throws Exception { SoftReference<String> sr = new SoftReference<String>("object"); Object o = sr.get(); if (o != null) { System.out.println(o); } else { System.out.println("collected or has been reclaimed"); } }
}</source>
Testing SoftReference
<source lang="java">
import java.lang.ref.PhantomReference; import java.lang.ref.Reference; import java.lang.ref.ReferenceQueue; import java.lang.ref.SoftReference; import java.lang.ref.WeakReference; import java.util.HashMap; public class Main {
public static void main(String[] args) { ReferenceQueue referenceQueue = new ReferenceQueue(); Object object = new Object() { public String toString() { return "Referenced Object"; } }; Object data = new Object() { public String toString() { return "Data"; } }; HashMap map = new HashMap(); Reference reference = new SoftReference(object, referenceQueue); map.put(reference, data); System.out.println(reference.get()); System.out.println(map.get(reference)); System.out.println(reference.isEnqueued()); System.gc(); System.out.println(reference.get()); System.out.println(map.get(reference)); System.out.println(reference.isEnqueued()); object = null; data = null; System.gc(); System.out.println(reference.get()); System.out.println(map.get(reference)); System.out.println(reference.isEnqueued()); }
}</source>