SETS AND MAPS - Introduction to Java Programming: Comprehensive Version - page 814

17 new TreeMap<>(hashMap);
18 System.out.println( "Display entries in ascending order of key" );
19 System.out.println(treeMap);
20
21 // Create a LinkedHashMap
22 Map<String, Integer> linkedHashMap =
23 new LinkedHashMap<>( 16 , 0.75f , true );
24 linkedHashMap.put( "Smith" , 30 );
25 linkedHashMap.put( "Anderson" , 31 );
26 linkedHashMap.put( "Lewis" , 29 );
27 linkedHashMap.put( "Cook" , 29 );
28
29 // Display the age for Lewis
30 System.out.println( "\nThe age for " + "Lewis is " +
31 linkedHashMap.get( "Lewis" ));
32
33 System.out.println( "Display entries in LinkedHashMap" );
34 System.out.println(linkedHashMap);
35 }
36 }

linked hash map

Display entries in HashMap
{Cook=29, Smith=30, Lewis=29, Anderson=31}

Display entries in ascending order of key
{Anderson=31, Cook=29, Lewis=29, Smith=30}

The age for Lewis is 29
Display entries in LinkedHashMap
{Smith=30, Anderson=31, Cook=29, Lewis=29}

As shown in the output, the entries in the HashMap are in random order. The entries in the
TreeMap are in increasing order of the keys. The entries in the LinkedHashMap are in the
order of their access, from least recently accessed to most recently.
All the concrete classes that implement the Map interface have at least two constructors.
One is the no-arg constructor that constructs an empty map, and the other constructs a map
from an instance of Map . Thus, new TreeMap<String, Integer>(hashMap) (lines 16-17)
constructs a tree map from a hash map.
You can create an insertion-ordered or access-ordered linked hash map. An access-ordered
linked hash map is created in lines 22-21. The most recently accessed entry is placed at the
end of the map. The entry with the key Lewis is last accessed in line 31, so it is displayed last
in line 34.

Tip
If you don't need to maintain an order in a map when updating it, use a HashMap .
When you need to maintain the insertion order or access order in the map, use a
LinkedHashMap . When you need the map to be sorted on keys, use a TreeMap .

21.18

✓ ✓

How do you create an instance of Map ? How do you add an entry to a map consisting
of a key and a value? How do you remove an entry from a map? How do you find the
size of a map? How do you traverse entries in a map?

Check

Point

21.19

Describe and compare HashMap , LinkedHashMap , and TreeMap .