Collecting Objects - Beginning Java 7 - page 496

• Formanyhashtables,aloadfactorof0.75isclosetooptimal.Thisvalueisthe
default for HashMap 's hashtable implementation.
HashMap supplies four constructors:
• HashMap() createsanew,emptyhashmapwithaninitialcapacityof16anda
load factor of 0.75.
• HashMap(int initialCapacity) creates a new, empty hashmap with
a capacity specified by initialCapacity and a load factor of 0.75. This
constructor throws IllegalArgumentException when initialCa-
pacity 's value is less than 0.
• HashMap(int initialCapacity, float loadFactor) createsa
new, empty hashmap with a capacity specified by initialCapacity and
a load factor specified by loadFactor . This constructor throws Illeg-
alArgumentException when initialCapacity islessthan0orwhen
loadFactor is less than or equal to 0.
• HashMap(Map<? extends K, ? extends V> m) creates a new
hashmap containing m 's entries. This constructor throws NullPointerEx-
ception when m contains the null reference.
Listing 5-19 demonstrates a hashmap.
Listing 5-19. Using a hashmap to count command-line arguments
import java.util.HashMap;
import java.util.Map;
class HashMapDemo
{
public static void main(String[] args)
{
Map<String, Integer> argMap = new HashMap<>();
for (String arg: args)
{
Integer count = argMap.get(arg);
argMap.put(arg, (count == null) ? 1 : count+1);
}
System.out.println(argMap);
System.out.println("Number of distinct arguments =