StaticBucketMap ("The Adobe AEM Quickstart and Web Application.")

java.lang.Object
- org.apache.commons.collections.map.StaticBucketMap

All Implemented Interfaces:

java.util.Map
```
public final class StaticBucketMap
extends java.lang.Object
implements java.util.Map
```
A StaticBucketMap is an efficient, thread-safe implementation of java.util.Map that performs well in in a highly thread-contentious environment. The map supports very efficient get, put, remove and containsKey operations, assuming (approximate) uniform hashing and that the number of entries does not exceed the number of buckets. If the number of entries exceeds the number of buckets or if the hash codes of the objects are not uniformly distributed, these operations have a worst case scenario that is proportional to the number of elements in the map (O(n)).
Each bucket in the hash table has its own monitor, so two threads can safely operate on the map at the same time, often without incurring any monitor contention. This means that you don't have to wrap instances of this class with Collections.synchronizedMap(Map); instances are already thread-safe. Unfortunately, however, this means that this map implementation behaves in ways you may find disconcerting. Bulk operations, such as putAll or the retainAll operation in collection views, are not atomic. If two threads are simultaneously executing
```
   staticBucketMapInstance.putAll(map);
 
```
and
```
   staticBucketMapInstance.entrySet().removeAll(map.entrySet());
 
```
then the results are generally random. Those two statement could cancel each other out, leaving staticBucketMapInstance essentially unchanged, or they could leave some random subset of map in staticBucketMapInstance.
Also, much like an encyclopedia, the results of size() and isEmpty() are out-of-date as soon as they are produced.
The iterators returned by the collection views of this class are not fail-fast. They will never raise a ConcurrentModificationException. Keys and values added to the map after the iterator is created do not necessarily appear during iteration. Similarly, the iterator does not necessarily fail to return keys and values that were removed after the iterator was created.
Finally, unlike HashMap-style implementations, this class never rehashes the map. The number of buckets is fixed at construction time and never altered. Performance may degrade if you do not allocate enough buckets upfront.
The atomic(Runnable) method is provided to allow atomic iterations and bulk operations; however, overuse of atomic will basically result in a map that's slower than an ordinary synchronized HashMap. Use this class if you do not require reliable bulk operations and iterations, or if you can make your own guarantees about how bulk operations will affect the map.
Since:

Commons Collections 3.0 (previously in main package v2.1)

Nested Class Summary
- Nested classes/interfaces inherited from interface java.util.Map
  java.util.Map.Entry<K,V>

Constructor Summary

Constructors
Constructor and Description
`StaticBucketMap()` Initializes the map with the default number of buckets (255).
`StaticBucketMap(int numBuckets)` Initializes the map with a specified number of buckets.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`atomic(java.lang.Runnable r)` Prevents any operations from occurring on this map while the given `Runnable` executes.
`void`	`clear()` Clears the map of all entries.
`boolean`	`containsKey(java.lang.Object key)` Checks if the map contains the specified key.
`boolean`	`containsValue(java.lang.Object value)` Checks if the map contains the specified value.
`java.util.Set`	`entrySet()` Gets the entry set.
`boolean`	`equals(java.lang.Object obj)` Compares this map to another, as per the Map specification.
`java.lang.Object`	`get(java.lang.Object key)` Gets the value associated with the key.
`int`	`hashCode()` Gets the hash code, as per the Map specification.
`boolean`	`isEmpty()` Checks if the size is currently zero.
`java.util.Set`	`keySet()` Gets the key set.
`java.lang.Object`	`put(java.lang.Object key, java.lang.Object value)` Puts a new key value mapping into the map.
`void`	`putAll(java.util.Map map)` Puts all the entries from the specified map into this map.
`java.lang.Object`	`remove(java.lang.Object key)` Removes the specified key from the map.
`int`	`size()` Gets the current size of the map.
`java.util.Collection`	`values()` Gets the values.

Methods inherited from class java.lang.Object
getClass, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Map
compute, computeIfAbsent, computeIfPresent, forEach, getOrDefault, merge, putIfAbsent, remove, replace, replace, replaceAll

- Constructor Detail
  - StaticBucketMap
```
public StaticBucketMap()
```
    Initializes the map with the default number of buckets (255).
  - StaticBucketMap
```
public StaticBucketMap(int numBuckets)
```
    Initializes the map with a specified number of buckets. The number of buckets is never below 17, and is always an odd number (StaticBucketMap ensures this). The number of buckets is inversely proportional to the chances for thread contention. The fewer buckets, the more chances for thread contention. The more buckets the fewer chances for thread contention.
    
    Parameters:
    
    numBuckets - the number of buckets for this map
- Method Detail
  - size
```
public int size()
```
    Gets the current size of the map. The value is computed fresh each time the method is called.
    
    Specified by:
    
    size in interface java.util.Map
    
    Returns:
    
    the current size
  - isEmpty
```
public boolean isEmpty()
```
    Checks if the size is currently zero.
    
    Specified by:
    
    isEmpty in interface java.util.Map
    
    Returns:
    
    true if empty
  - get
```
public java.lang.Object get(java.lang.Object key)
```
    Gets the value associated with the key.
    
    Specified by:
    
    get in interface java.util.Map
    
    Parameters:
    
    key - the key to retrieve
    
    Returns:
    
    the associated value
  - containsKey
```
public boolean containsKey(java.lang.Object key)
```
    Checks if the map contains the specified key.
    
    Specified by:
    
    containsKey in interface java.util.Map
    
    Parameters:
    
    key - the key to check
    
    Returns:
    
    true if found
  - containsValue
```
public boolean containsValue(java.lang.Object value)
```
    Checks if the map contains the specified value.
    
    Specified by:
    
    containsValue in interface java.util.Map
    
    Parameters:
    
    value - the value to check
    
    Returns:
    
    true if found
  - put
```
public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)
```
    Puts a new key value mapping into the map.
    
    Specified by:
    
    put in interface java.util.Map
    
    Parameters:
    
    key - the key to use
    
    value - the value to use
    
    Returns:
    
    the previous mapping for the key
  - remove
```
public java.lang.Object remove(java.lang.Object key)
```
    Removes the specified key from the map.
    
    Specified by:
    
    remove in interface java.util.Map
    
    Parameters:
    
    key - the key to remove
    
    Returns:
    
    the previous value at this key
  - keySet
```
public java.util.Set keySet()
```
    Gets the key set.
    
    Specified by:
    
    keySet in interface java.util.Map
    
    Returns:
    
    the key set
  - values
```
public java.util.Collection values()
```
    Gets the values.
    
    Specified by:
    
    values in interface java.util.Map
    
    Returns:
    
    the values
  - entrySet
```
public java.util.Set entrySet()
```
    Gets the entry set.
    
    Specified by:
    
    entrySet in interface java.util.Map
    
    Returns:
    
    the entry set
  - putAll
```
public void putAll(java.util.Map map)
```
    Puts all the entries from the specified map into this map. This operation is not atomic and may have undesired effects.
    
    Specified by:
    
    putAll in interface java.util.Map
    
    Parameters:
    
    map - the map of entries to add
  - clear
```
public void clear()
```
    Clears the map of all entries.
    
    Specified by:
    
    clear in interface java.util.Map
  - equals
```
public boolean equals(java.lang.Object obj)
```
    Compares this map to another, as per the Map specification.
    
    Specified by:
    
    equals in interface java.util.Map
    
    Overrides:
    
    equals in class java.lang.Object
    
    Parameters:
    
    obj - the object to compare to
    
    Returns:
    
    true if equal
  - hashCode
```
public int hashCode()
```
    Gets the hash code, as per the Map specification.
    
    Specified by:
    
    hashCode in interface java.util.Map
    
    Overrides:
    
    hashCode in class java.lang.Object
    
    Returns:
    
    the hash code
  - atomic
```
public void atomic(java.lang.Runnable r)
```
    Prevents any operations from occurring on this map while the given Runnable executes. This method can be used, for instance, to execute a bulk operation atomically:
```
    staticBucketMapInstance.atomic(new Runnable() {
        public void run() {
            staticBucketMapInstance.putAll(map);
        }
    });
  
```
    It can also be used if you need a reliable iterator:
```
    staticBucketMapInstance.atomic(new Runnable() {
        public void run() {
            Iterator iterator = staticBucketMapInstance.iterator();
            while (iterator.hasNext()) {
                foo(iterator.next();
            }
        }
    });
  
```
    Implementation note: This method requires a lot of time and a ton of stack space. Essentially a recursive algorithm is used to enter each bucket's monitor. If you have twenty thousand buckets in your map, then the recursive method will be invoked twenty thousand times. You have been warned.
    Parameters:
    
    r - the code to execute atomically

Class StaticBucketMap

Nested Class Summary

Nested classes/interfaces inherited from interface java.util.Map

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Methods inherited from interface java.util.Map

Constructor Detail

StaticBucketMap

StaticBucketMap

Method Detail

size

isEmpty

get

containsKey

containsValue

put

remove

keySet

values

entrySet

putAll

clear

equals

hashCode

atomic