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CacheMap.javaAPI DocJava SE 6 API3366Tue Jun 10 00:22:04 BST 2008com.sun.jmx.remote.util

CacheMap

public class CacheMap extends WeakHashMap

Like WeakHashMap, except that the keys of the n most recently-accessed entries are kept as {@link SoftReference soft references}. Accessing an element means creating it, or retrieving it with {@link #get(Object) get}. Because these entries are kept with soft references, they will tend to remain even if their keys are not referenced elsewhere. But if memory is short, they will be removed.

Fields Summary
private final LinkedList
cache
private final int
nSoftReferences
Constructors Summary
public CacheMap(int nSoftReferences)

Create a CacheMap that can keep up to nSoftReferences as soft references.

param
nSoftReferences Maximum number of keys to keep as soft references. Access times for {@link #get(Object) get} and {@link #put(Object, Object) put} have a component that scales linearly with nSoftReferences, so this value should not be too great.
throws
IllegalArgumentException if nSoftReferences is negative.

	if (nSoftReferences < 0) {
	    throw new IllegalArgumentException("nSoftReferences = " +
					       nSoftReferences);
	}
	this.nSoftReferences = nSoftReferences;
Methods Summary
private voidcache(java.lang.Object key)

	Iterator it = cache.iterator();
	while (it.hasNext()) {
            SoftReference sref = (SoftReference) it.next();
            Object key1 = sref.get();
	    if (key1 == null)
                it.remove();
	    else if (key.equals(key1)) {
		// Move this element to the head of the LRU list
		it.remove();
		cache.add(0, sref);
		return;
	    }
	}

	int size = cache.size();
	if (size == nSoftReferences) {
	    if (size == 0)
		return;  // degenerate case, equivalent to WeakHashMap
	    it.remove();
	}

	cache.add(0, new SoftReference(key));
public java.lang.Objectget(java.lang.Object key)

	cache(key);
	return super.get(key);
public java.lang.Objectput(java.lang.Object key, java.lang.Object value)

	cache(key);
	return super.put(key, value);