How to implement HashMap, LinkedHashMap and TreeMap in JShell in Java 9?

JShell是Java 9中引入的命令行提示工具，也称为REPL 评估简单语句、执行它并立即打印输出的工具。

Map 接口指定一个契约，以键/值的形式实现元素集合对。实现Map接口的Java集合类有HashMap、LinkedHashMap和TreeMap。

在下面的代码片段中，HashMap的元素不保证以插入顺序或键的排序顺序存储。

Snippet-1

<strong>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}</strong>

在下面的代码片段中，LinkedHashMap的元素已存储在插入中订单。

Snippet-2

<strong>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}</strong>

在下面的代码片段中，TreeMap 的元素已按键的自然排序顺序存储。

代码片段-3

<strong>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}</strong>

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