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How to implement HashMap, LinkedHashMap, and TreeMap in JShell in Java 9?
JShell is a command-line prompt tool introduced in Java 9, and it is also called a REPL tool to evaluate simple statements, executes it, and print the output immediately.
A Map interface specifies a contract to implement collections of elements in the form of key/value pairs. Java collection classes that implement the Map interface are HashMap, LinkedHashMap, and TreeMap.
In the below code snippet, the elements of HashMap are not guaranteed to store either in an insertion order or in the sorted order of keys.
Snippet-1
jshell> HashMap<String, Integer> hashMap = new HashMap<>();
hashMap ==> {}
jshell> hashMap.put("Adithya", 101);
$2 ==> null
jshell> hashMap.put("Jai", 102);
$3 ==> null
jshell> hashMap.put("Chaitanya", 103);
$4 ==> null
jshell> hashMap.put("Ravi", 104);
$5 ==> null
jshell> hashMap
hashMap ==> {Chaitanya=103, Jai=102, Ravi=104, Adithya=101}In the below code snippet, the elements of LinkedHashMap have stored in the insertion order.
Snippet-2
jshell> LinkedHashMap<String, Integer> linkedHashMap = new LinkedHashMap<>();
linkedHashMap ==> {}
jshell> linkedHashMap.put("Raja", 101);
$8 ==> null
jshell> linkedHashMap.put("Adithya", 102);
$9 ==> null
jshell> linkedHashMap.put("Surya", 103);
$10 ==> null
jshell> linkedHashMap.put("Vamsi", 104);
$11 ==> null
jshell> linkedHashMap
linkedHashMap ==> {Raja=101, Adithya=102, Surya=103, Vamsi=104}In the below code snippet, the elements of TreeMap have stored in the natural sorted order of keys.
Snippet-3
jshell> TreeMap<String, Integer> treeMap = new TreeMap<>();
treeMap ==> {}
jshell> treeMap.put("Raj", 101);
$14 ==> null
jshell> treeMap.put("Pavan", 102);
$15 ==> null
jshell> treeMap.put("Arjun", 103);
$16 ==> null
jshell> treeMap.put("Manoj", 104);
$17 ==> null
jshell> treeMap
treeMap ==> {Arjun=103, Manoj=104, Pavan=102, Raj=101}
Updated on: 01-May-2020
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