Đưa ra điều này:
public class SalesTerritory
{
private String territoryName;
private Set<String> geographicExtents;
public SalesTerritory( String territoryName, Set<String> zipCodes )
{
this.territoryName = territoryName;
this.geographicExtents = zipCodes;
}
public String getTerritoryName()
{
return territoryName;
}
public void setTerritoryName( String territoryName )
{
this.territoryName = territoryName;
}
public Set<String> getGeographicExtents()
{
return geographicExtents != null ? Collections.unmodifiableSet( geographicExtents ) : Collections.emptySet();
}
public void setGeographicExtents( Set<String> geographicExtents )
{
this.geographicExtents = new HashSet<>( geographicExtents );
}
@Override
public int hashCode()
{
int hash = 7;
hash = 53 * hash + Objects.hashCode( this.territoryName );
return hash;
}
@Override
public boolean equals( Object obj )
{
if ( this == obj ) {
return true;
}
if ( obj == null ) {
return false;
}
if ( getClass() != obj.getClass() ) {
return false;
}
final SalesTerritory other = (SalesTerritory) obj;
if ( !Objects.equals( this.territoryName, other.territoryName ) ) {
return false;
}
return true;
}
@Override
public String toString()
{
return "SalesTerritory{" + "territoryName=" + territoryName + ", geographicExtents=" + geographicExtents + '}';
}
}
và điều này:
public class SalesTerritories
{
private static final Set<SalesTerritory> territories
= new HashSet<>(
Arrays.asList(
new SalesTerritory[]{
new SalesTerritory( "North-East, USA",
new HashSet<>( Arrays.asList( new String[]{ "Maine", "New Hampshire", "Vermont",
"Rhode Island", "Massachusetts", "Connecticut",
"New York", "New Jersey", "Delaware", "Maryland",
"Eastern Pennsylvania", "District of Columbia" } ) ) ),
new SalesTerritory( "Appalachia, USA",
new HashSet<>( Arrays.asList( new String[]{ "West-Virgina", "Kentucky",
"Western Pennsylvania" } ) ) ),
new SalesTerritory( "South-East, USA",
new HashSet<>( Arrays.asList( new String[]{ "Virginia", "North Carolina", "South Carolina",
"Georgia", "Florida", "Alabama", "Tennessee",
"Mississippi", "Arkansas", "Louisiana" } ) ) ),
new SalesTerritory( "Mid-West, USA",
new HashSet<>( Arrays.asList( new String[]{ "Ohio", "Michigan", "Wisconsin", "Minnesota",
"Iowa", "Missouri", "Illinois", "Indiana" } ) ) ),
new SalesTerritory( "Great Plains, USA",
new HashSet<>( Arrays.asList( new String[]{ "Oklahoma", "Kansas", "Nebraska",
"South Dakota", "North Dakota",
"Eastern Montana",
"Wyoming", "Colorada" } ) ) ),
new SalesTerritory( "Rocky Mountain, USA",
new HashSet<>( Arrays.asList( new String[]{ "Western Montana", "Idaho", "Utah", "Nevada" } ) ) ),
new SalesTerritory( "South-West, USA",
new HashSet<>( Arrays.asList( new String[]{ "Arizona", "New Mexico", "Texas" } ) ) ),
new SalesTerritory( "Pacific North-West, USA",
new HashSet<>( Arrays.asList( new String[]{ "Washington", "Oregon", "Alaska" } ) ) ),
new SalesTerritory( "Pacific South-West, USA",
new HashSet<>( Arrays.asList( new String[]{ "California", "Hawaii" } ) ) )
}
)
);
public static Set<SalesTerritory> getAllTerritories()
{
return Collections.unmodifiableSet( territories );
}
private SalesTerritories()
{
}
}
Sau đó, chúng tôi có thể làm điều này:
System.out.println();
System.out
.println( "We can use 'flatMap' in combination with the 'AbstractMap.SimpleEntry' class to flatten a hierarchical data-structure to a set of Key/Value pairs..." );
SalesTerritories.getAllTerritories()
.stream()
.flatMap( t -> t.getGeographicExtents()
.stream()
.map( ge -> new SimpleEntry<>( t.getTerritoryName(), ge ) )
)
.map( e -> String.format( "%-30s : %s",
e.getKey(),
e.getValue() ) )
.forEach( System.out::println );