Utility methods for operating on memory-efficient maps. : Customized Map « Collections Data Structure « Java

Home
Java
1.2D Graphics GUI
2.3D
3.Advanced Graphics
4.Ant
5.Apache Common
6.Chart
7.Class
8.Collections Data Structure
9.Data Type
10.Database SQL JDBC
11.Design Pattern
12.Development Class
13.EJB3
14.Email
15.Event
16.File Input Output
17.Game
18.Generics
19.GWT
20.Hibernate
21.I18N
22.J2EE
23.J2ME
24.JDK 6
25.JNDI LDAP
26.JPA
27.JSP
28.JSTL
29.Language Basics
30.Network Protocol
31.PDF RTF
32.Reflection
33.Regular Expressions
34.Scripting
35.Security
36.Servlets
37.Spring
38.Swing Components
39.Swing JFC
40.SWT JFace Eclipse
41.Threads
42.Tiny Application
43.Velocity
44.Web Services SOA
45.XML
Java » Collections Data Structure » Customized MapScreenshots 
Utility methods for operating on memory-efficient maps.
    



import java.util.Collections;
import java.util.HashMap;
import java.util.Map;

/**
 * Utility methods for operating on memory-efficient maps. All maps of size 0 or
 * 1 are assumed to be immutable. All maps of size greater than 1 are assumed to
 * be mutable.
 */
public class Maps {

  private static final Class<?> MULTI_MAP_CLASS = HashMap.class;
  private static final Class<?> SINGLETON_MAP_CLASS = Collections.singletonMap(
      null, null).getClass();

  public static <K, V> Map<K, V> create() {
    return Collections.emptyMap();
  }

  public static <K, V> Map<K, V> create(K key, V value) {
    return Collections.singletonMap(key, value);
  }

  public static <K, V> Map<K, V> normalize(Map<K, V> map) {
    switch (map.size()) {
      case 0:
        return create();
      case 1{
        if (map.getClass() == SINGLETON_MAP_CLASS) {
          return map;
        }
        K key = map.keySet().iterator().next();
        return create(key, map.get(key));
      }
      default:
        if (map.getClass() == MULTI_MAP_CLASS) {
          return map;
        }
        return new HashMap<K, V>(map);
    }
  }

  public static <K, V> Map<K, V> normalizeUnmodifiable(Map<K, V> map) {
    if (map.size() 2) {
      return normalize(map);
    else {
      // TODO: implement an UnmodifiableHashMap?
      return Collections.unmodifiableMap(normalize(map));
    }
  }

  public static <K, V> Map<K, V> put(Map<K, V> map, K key, V value) {
    switch (map.size()) {
      case 0:
        // Empty -> Singleton
        return Collections.singletonMap(key, value);
      case 1{
        if (map.containsKey(key)) {
          return create(key, value);
        }
        // Singleton -> HashMap
        Map<K, V> result = new HashMap<K, V>();
        result.put(map.keySet().iterator().next(),
            map.values().iterator().next());
        result.put(key, value);
        return result;
      }
      default:
        // HashMap
        map.put(key, value);
        return map;
    }
  }

  public static <K, V> Map<K, V> putAll(Map<K, V> map, Map<K, V> toAdd) {
    switch (toAdd.size()) {
      case 0:
        // No-op.
        return map;
      case 1{
        // Add one element.
        K key = toAdd.keySet().iterator().next();
        return put(map, key, toAdd.get(key));
      }
      default:
        // True list merge, result >= 2.
        switch (map.size()) {
          case 0:
            return new HashMap<K, V>(toAdd);
          case 1{
            HashMap<K, V> result = new HashMap<K, V>();
            K key = map.keySet().iterator().next();
            result.put(key, map.get(key));
            result.putAll(toAdd);
            return normalize(result);
          }
          default:
            map.putAll(toAdd);
            return map;
        }
    }
  }

  public static <K, V> Map<K, V> remove(Map<K, V> map, K key) {
    switch (map.size()) {
      case 0:
        // Empty
        return map;
      case 1:
        // Singleton -> Empty
        if (map.containsKey(key)) {
          return create();
        }
        return map;
      case 2:
        // HashMap -> Singleton
        if (map.containsKey(key)) {
          map.remove(key);
          key = map.keySet().iterator().next();
          return create(key, map.get(key));
        }
        return map;
      default:
        // IdentityHashMap
        map.remove(key);
        return map;
    }
  }
}

   
    
    
    
  
Related examples in the same category
1.Ordered Map
2.Case Insensitive Map
3.A Map collection with real-time behavior
4.Cache Map
5.Map implementation Optimized for Strings keys
6.An integer hashmap
7.An IdentityMap that uses reference-equality instead of object-equality
8.Int Object HashMap
9.Concurrent Skip List Map
10.A hash map that uses primitive ints for the key rather than objects.
11.Integer Map
12.Copy On Write Map
13.Expiring Map
14.Array Map
15.Int Object HashMap (from CERN)
16.Int HashMap from jodd.org
17.String Map
18.List Map
19.Map using Locale objects as keys
20.Map with keys iterated in insertion order
21.Most Recently Used Map
22.Multi Map
23.MultiMap is a Java version of the C++ STL class std::multimap
24.Object Int Map
25.Sequenced HashMap
26.Int Int Map
27.Int Object Map
28.Identity HashMap
29.A java.util.Map interface which can only hold a single object
30.A multi valued Map
31.A simple hashmap from keys to integers
32.A memory-efficient hash map.
33.An implementation of the java.util.Map interface which can only hold a single object.
34.CaseBlindHashMap - a HashMap extension, using Strings as key values.
35.A fixed size map implementation.
36.Int HashMap
37.IntMap provides a simple hashmap from keys to integers
38.Complex Key HashMap
39.A Map with multiple values for a key
40.A Map that accepts int or Integer keys only
41.A Map where keys are compared by object identity, rather than equals()
42.Type-safe Map, from char array to String value
43.A hashtable-based Map implementation with soft keys
44.List ordered map
45.Hash map using String values as keys mapped to primitive int values.
46.Lookup table that stores a list of strings
47.HashNMap stores multiple values by a single key value. Values can be retrieved using a direct query or by creating an enumeration over the stored elements.
48.Combines multiple values to form a single composite key. MultiKey can often be used as an alternative to nested maps.
java2s.com  | Contact Us | Privacy Policy
Copyright 2009 - 12 Demo Source and Support. All rights reserved.
All other trademarks are property of their respective owners.