Examples of java.lang.ref.SoftReference

java.lang.ref.SoftReference
Soft reference objects, which are cleared at the discretion of the garbage collector in response to memory demand. Soft references are most often used to implement memory-sensitive caches.
Suppose that the garbage collector determines at a certain point in time that an object is softly reachable. At that time it may choose to clear atomically all soft references to that object and all soft references to any other softly-reachable objects from which that object is reachable through a chain of strong references. At the same time or at some later time it will enqueue those newly-cleared soft references that are registered with reference queues.
All soft references to softly-reachable objects are guaranteed to have been cleared before the virtual machine throws an OutOfMemoryError. Otherwise no constraints are placed upon the time at which a soft reference will be cleared or the order in which a set of such references to different objects will be cleared. Virtual machine implementations are, however, encouraged to bias against clearing recently-created or recently-used soft references.
Direct instances of this class may be used to implement simple caches; this class or derived subclasses may also be used in larger data structures to implement more sophisticated caches. As long as the referent of a soft reference is strongly reachable, that is, is actually in use, the soft reference will not be cleared. Thus a sophisticated cache can, for example, prevent its most recently used entries from being discarded by keeping strong referents to those entries, leaving the remaining entries to be discarded at the discretion of the garbage collector. @version 1.36, 02/26/09 @author Mark Reinhold @since 1.2

            Object referent = reference.get();
            ImagingListenerImpl listener;
            if (referent == null) {
                // First invocation or SoftReference has been cleared.
                reference =
                    new SoftReference(listener = new ImagingListenerImpl());
            } else {
                // SoftReference has not been cleared.
                listener = (ImagingListenerImpl)referent;
            }

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        ZipEntry entry = zipFile.getEntry("META-INF/MANIFEST.MF");


        // Get a buffer for this thread if there is one already otherwise,
        // create one of size DEFAULT_BUFFER (64K) if the manifest is less
        // than 64k or of the size of the manifest.
        SoftReference ref = (SoftReference) m_defaultBuffer.get();
        byte[] bytes = null;
        if (ref != null)
        {
            bytes = (byte[]) ref.get();
        }
        int size = (int) entry.getSize();
        if (bytes == null)
        {
            bytes = new byte[size > DEFAULT_BUFFER ? size : DEFAULT_BUFFER];
            m_defaultBuffer.set(new SoftReference(bytes));
        }
        else if (size > bytes.length)
        {
            bytes = new byte[size];
            m_defaultBuffer.set(new SoftReference(bytes));
        }


        // Now read in the manifest in one go into the bytes array.
        // The InputStream is already
        // buffered and can handle up to 64K buffers in one go.

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            }
        }


        try
        {
            SoftReference collectionEntry = null;


            PermissionCollection collection = null;


            synchronized (m_cache)
            {
                collectionEntry = (SoftReference) m_cache.get(targetClass);
            }


            if (collectionEntry != null)
            {
                collection = (PermissionCollection) collectionEntry.get();
            }


            if (collection == null)
            {
                collection = target.newPermissionCollection();


                if (collection == null)
                {
                    collection = new DefaultPermissionCollection();
                }


                for (int i = 0; i < m_permissionInfos.length; i++)
                {
                    PermissionInfo permissionInfo = m_permissionInfos[i];
                    String infoType = permissionInfo.getType();
                    String permissionType = targetClass.getName();


                    if (infoType.equals(permissionType))
                    {
                        Permission permission = createPermission(
                            permissionInfo, targetClass);


                        if (permission != null)
                        {
                            collection.add(permission);
                        }
                    }
                }


                synchronized (m_cache)
                {
                    m_cache.put(new Entry(target.getClass(), m_queue),
                        new SoftReference(collection));
                }
            }


            return collection.implies(target);
        }

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    private Permission getFromCache(String encoded, Class target)
    {
        synchronized (m_permissionCache)
        {
            SoftReference ref = (SoftReference) m_permissionCache.get(encoded);
            if (ref != null)
            {
                Map inner = (Map) ref.get();
                if (inner != null)
                {
                    Entry entry = (Entry) inner.get(target);
                    if (entry != null)
                    {

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    public void bundleChanged( BundleEvent event )
    {
        if ( event.getType() == BundleEvent.STOPPING )
        {
            SoftReference mtir = ( SoftReference ) this.bundleMetaTypeInformation.remove( new Long( event.getBundle()
                .getBundleId() ) );
            if ( mtir != null )
            {
                MetaTypeInformationImpl mti = ( MetaTypeInformationImpl ) mtir.get();
                if ( mti != null )
                {
                    mti.dispose();
                }
            }

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                }
            }
        }


        this.bundleMetaTypeInformation.put( new Long( bundle.getBundleId() ),
            new SoftReference( mti ) );
    }

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    }




    private MetaTypeInformationImpl getMetaTypeInformationInternal( final Bundle bundle )
    {
        SoftReference mtir = ( SoftReference ) this.bundleMetaTypeInformation.get( new Long( bundle.getBundleId() ) );
        return ( MetaTypeInformationImpl ) ( ( mtir == null ) ? null : mtir.get() );
    }

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                for (int i = 0; i < numSuppressedKeys; i++) {
                    suppressedKeys.add(SUPPRESSED_KEYS[i]);
                }


                // Cache the Vector of suppressed keys.
                suppressedKeyReference = new SoftReference(suppressedKeys);
            }
        }


        return suppressedKeys;
    }

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                    }
                }
            }


            // Cache the table.
            hintTableReference = new SoftReference(table);
        }


        return table;
    }

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                for(int i = 0; i < numSuppressedKeys; i++) {
                    suppressedKeys.add(SUPPRESSED_KEYS[i]);
                }


                // Cache the Vector of suppressed keys.
                suppressedKeyReference = new SoftReference(suppressedKeys);
            }
        }


        return suppressedKeys;
    }

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