Re: Generics for a multiplevalue hashmap

From: (Stefan Ram)
19 Jul 2011 17:05:04 GMT
<> (Stefan Ram) writes:

Alexis Berry <> writes:

public class MultipleValueHashMap<T, java.util.List<U>> implements Map<T, java.util.List<U>> {

I'd just use:

  For example:

public class Main
  public static void main( final java.lang.String[] args )
    final Multimap<java.lang.Integer,java.lang.Integer> m
    = new DefaultSetMap<java.lang.Integer,java.lang.Integer>();
    m.add( 1, 1 ); m.add( 2, 2 ); m.add( 2, 3 );
    java.lang.System.out.println( m ); }}

  This prints:

{1=[1], 2=[2, 3]}

  Rest of the source code (I suggest to quote only parts one
  directly refers to):

interface Container<V>
{ public void add( final V v );
  public java.lang.String toString(); }

interface ContainerFactory<V>
{ public Container<V> newContainer(); }

class DefaultContainer<V> implements Container<V>
{ final java.util.Set<V> set;
  public DefaultContainer()
  { this.set = new java.util.HashSet<V>(); }
  public void add( final V v )
  { this.set.add( v ); }
  public java.lang.String toString()
  { return this.set.toString(); }}

class DefaultContainerFactory<V> implements ContainerFactory<V>
{ public DefaultContainer<V> newContainer()
  { return new DefaultContainer<V>(); }}

interface Multimap<D,V>
{ public void add( final D d, final V v );
  public java.lang.String toString(); }

class DefaultMultimap<D,V> implements Multimap<D,V>
{ final java.util.Map<D,Container<V>> map;
  final ContainerFactory<V> containerFactory;
  public DefaultMultimap
  ( final java.util.Map<D,Container<V>> map,
    final ContainerFactory<V> containerFactory )
  { = map;
    this.containerFactory = containerFactory; }
  public boolean exists( final D d ){ return d ); }
  public Container<V> get( final D d ){ return d ); }
  public void set( final D d, final Container<V> v )
  { d, v ); }
  public void add( final D d, final V v )
  { if( !this.exists( d ))this.set( d, this.containerFactory.newContainer() );
    this.get( d ).add( v ); }
  public java.lang.String toString()
  { return; }}

class DefaultSetMap<D,V> implements Multimap<D,V>
{ final Multimap<D,V> multimap;
  public DefaultSetMap()
  { this.multimap = new DefaultMultimap<D,V>
    ( new java.util.HashMap<D,Container<V>>(),
      new DefaultContainerFactory<V>() ); }
  public void add( final D d, final V v )
  { this.multimap.add( d, v ); }
  public java.lang.String toString()
  { return this.multimap.toString(); }}

  One can observe that DefaultMultimap<D,V> is defined without any
  fixed container for the multiple values of a key. Such a container
  is only added in DefaultSetMap<D,V>.

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