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  /*
   * Copyright (C) 2011 The Android Open Source Project
   *
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
 
 package org.gawst.asyncdb;
 
 import java.util.Map;

Static library version of android.util.LruCache. Used to write apps that run on API levels prior to 12. When running on API level 12 or above, this implementation is still used; it does not try to switch to the framework's implementation. See the framework SDK documentation for a class overview.
 
 public class LruCache<K, V> {
     private final LinkedHashMap<K, V> map;

    
Size of this cache in units. Not necessarily the number of elements.
 
     private int size;
     private int maxSize;
 
     private int putCount;
     private int createCount;
     private int evictionCount;
     private int hitCount;
     private int missCount;

    

Parameters:
maxSize for caches that do not override sizeOf(java.lang.Object,java.lang.Object), this is the maximum number of entries in the cache. For all other caches, this is the maximum sum of the sizes of the entries in this cache.
 
     public LruCache(int maxSize) {
         if (maxSize <= 0) {
             throw new IllegalArgumentException("maxSize <= 0");
         }
         this. = maxSize;
         this. = new LinkedHashMap<K, V>(0, 0.75f, true);
     }

    
Returns the value for key if it exists in the cache or can be created by #create. If a value was returned, it is moved to the head of the queue. This returns null if a value is not cached and cannot be created.
 
     public final V get(K key) {
         if (key == null) {
             throw new NullPointerException("key == null");
         }
 
         V mapValue;
         synchronized (this) {
             mapValue = .get(key);
             if (mapValue != null) {
                 ++;
                 return mapValue;
             }
             ++;
         }
 
         /*
          * Attempt to create a value. This may take a long time, and the map
          * may be different when create() returns. If a conflicting value was
          * added to the map while create() was working, we leave that value in
          * the map and release the created value.
          */
 
         V createdValue = create(key);
         if (createdValue == null) {
             return null;
         }
 
         synchronized (this) {
             ++;
             mapValue = .put(keycreatedValue);
 
             if (mapValue != null) {
                 // There was a conflict so undo that last put
                 .put(keymapValue);
             } else {
                  += safeSizeOf(keycreatedValue);
             }
         }
 
        if (mapValue != null) {
            entryRemoved(falsekeycreatedValuemapValue);
            return mapValue;
        } else {
            trimToSize();
            return createdValue;
        }
    }

    
Caches value for key. The value is moved to the head of the queue.

Returns:
the previous value mapped by key.
    public final V put(K key, V value) {
        if (key == null || value == null) {
            throw new NullPointerException("key == null || value == null");
        }
        V previous;
        synchronized (this) {
            ++;
             += safeSizeOf(keyvalue);
            previous = .put(keyvalue);
            if (previous != null) {
                 -= safeSizeOf(keyprevious);
            }
        }
        if (previous != null) {
            entryRemoved(falsekeypreviousvalue);
        }
        trimToSize();
        return previous;
    }

    
Remove the eldest entries until the total of remaining entries is at or below the requested size.

Parameters:
maxSize the maximum size of the cache before returning. May be -1 to evict even 0-sized elements.
    public void trimToSize(int maxSize) {
        while (true) {
            K key;
            V value;
            synchronized (this) {
                if ( < 0 || (.isEmpty() &&  != 0)) {
                    throw new IllegalStateException(getClass().getName()
                            + ".sizeOf() is reporting inconsistent results!");
                }
                if ( <= maxSize || .isEmpty()) {
                    break;
                }
                Map.Entry<K, V> toEvict = .entrySet().iterator().next();
                key = toEvict.getKey();
                value = toEvict.getValue();
                .remove(key);
                 -= safeSizeOf(keyvalue);
                ++;
            }
            entryRemoved(truekeyvaluenull);
        }
    }

    
Removes the entry for key if it exists.

Returns:
the previous value mapped by key.
    public final V remove(K key) {
        if (key == null) {
            throw new NullPointerException("key == null");
        }
        V previous;
        synchronized (this) {
            previous = .remove(key);
            if (previous != null) {
                 -= safeSizeOf(keyprevious);
            }
        }
        if (previous != null) {
            entryRemoved(falsekeypreviousnull);
        }
        return previous;
    }

    
Called for entries that have been evicted or removed. This method is invoked when a value is evicted to make space, removed by a call to remove(java.lang.Object), or replaced by a call to put(java.lang.Object,java.lang.Object). The default implementation does nothing.

The method is called without synchronization: other threads may access the cache while this method is executing.

Parameters:
evicted true if the entry is being removed to make space, false if the removal was caused by a put(java.lang.Object,java.lang.Object) or remove(java.lang.Object).
newValue the new value for key, if it exists. If non-null, this removal was caused by a put(java.lang.Object,java.lang.Object). Otherwise it was caused by an eviction or a remove(java.lang.Object).
    protected void entryRemoved(boolean evicted, K key, V oldValue, V newValue) {}

    
Called after a cache miss to compute a value for the corresponding key. Returns the computed value or null if no value can be computed. The default implementation returns null.

The method is called without synchronization: other threads may access the cache while this method is executing.

If a value for key exists in the cache when this method returns, the created value will be released with entryRemoved(boolean,java.lang.Object,java.lang.Object,java.lang.Object) and discarded. This can occur when multiple threads request the same key at the same time (causing multiple values to be created), or when one thread calls put(java.lang.Object,java.lang.Object) while another is creating a value for the same key.

    protected V create(K key) {
        return null;
    }
    private int safeSizeOf(K key, V value) {
        int result = sizeOf(keyvalue);
        if (result < 0) {
            throw new IllegalStateException("Negative size: " + key + "=" + value);
        }
        return result;
    }

    
Returns the size of the entry for key and value in user-defined units. The default implementation returns 1 so that size is the number of entries and max size is the maximum number of entries.

An entry's size must not change while it is in the cache.

    protected int sizeOf(K key, V value) {
        return 1;
    }

    
Clear the cache, calling entryRemoved(boolean,java.lang.Object,java.lang.Object,java.lang.Object) on each removed entry.
    public final void evictAll() {
        trimToSize(-1); // -1 will evict 0-sized elements
    }

    
For caches that do not override sizeOf(java.lang.Object,java.lang.Object), this returns the number of entries in the cache. For all other caches, this returns the sum of the sizes of the entries in this cache.
    public synchronized final int size() {
        return ;
    }

    
For caches that do not override sizeOf(java.lang.Object,java.lang.Object), this returns the maximum number of entries in the cache. For all other caches, this returns the maximum sum of the sizes of the entries in this cache.
    public synchronized final int maxSize() {
        return ;
    }

    
Returns the number of times get(java.lang.Object) returned a value.
    public synchronized final int hitCount() {
        return ;
    }

    
Returns the number of times get(java.lang.Object) returned null or required a new value to be created.
    public synchronized final int missCount() {
        return ;
    }

    
Returns the number of times create(java.lang.Object) returned a value.
    public synchronized final int createCount() {
        return ;
    }

    
Returns the number of times put(java.lang.Object,java.lang.Object) was called.
    public synchronized final int putCount() {
        return ;
    }

    
Returns the number of values that have been evicted.
    public synchronized final int evictionCount() {
        return ;
    }

    
Returns a copy of the current contents of the cache, ordered from least recently accessed to most recently accessed.
    public synchronized final Map<K, V> snapshot() {
        return new LinkedHashMap<K, V>();
    }
    @Override public synchronized final String toString() {
        int accesses =  + ;
        int hitPercent = accesses != 0 ? (100 *  / accesses) : 0;
        return String.format("LruCache[maxSize=%d,hits=%d,misses=%d,hitRate=%d%%]",
                hitPercent);
    }
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