add ConcurrentHashMap example

realDuYuanChao · realDuYuanChao · commit 869fbffaf985 · 2020-12-01T10:57:21.000+08:00
diff --git a/src/main/java/com/examplehub/basics/ConcurrentHashMapExample.java b/src/main/java/com/examplehub/basics/ConcurrentHashMapExample.java
@@ -0,0 +1,50 @@
+package com.examplehub.basics;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class ConcurrentHashMapExample {
+  public static void main(String[] args) {
+    ConcurrentHashMap<Integer, String> map = new ConcurrentHashMap<>();
+    map.put(1, "Java");
+    map.put(2, "Go");
+    map.put(3, "Python");
+    System.out.println(map); /* {1=Java, 2=Go, 3=Python} */
+
+    map.putIfAbsent(3, "python");
+    System.out.println(map); /* {1=Java, 2=Go, 3=Python} */
+    map.putIfAbsent(4, "HTML");
+    System.out.println(map); /* {1=Java, 2=Go, 3=Python, 4=HTML} */
+
+    map.replace(4, "HTML5");
+    System.out.println(map); /* {1=Java, 2=Go, 3=Python, 4=HTML5} */
+
+    System.out.print("all keys: ");
+    for (int key : map.keySet()) {
+      System.out.print(key + " ");
+    }
+    System.out.println(); /* all keys: 1 2 3 4  */
+
+    /*
+    key = 1, value = Java
+    key = 2, value = Go
+    key = 3, value = Python
+    key = 4, value = HTML5
+    */
+    for (Map.Entry<Integer, String> entry : map.entrySet()) {
+      System.out.println(
+          "key = ".concat(entry.getKey() + "").concat(", value = ").concat(entry.getValue()));
+    }
+
+
+
+    System.out.println(map.get(3)); /* Python */
+    System.out.println(map.getOrDefault(100, "Default value")); /* Default value */
+
+    System.out.println(map.remove(3)); /* Python */
+    System.out.println(map.remove(1, "Java")); /* true */
+    System.out.println(map); /* {2=Go, 4=HTML5} */
+    map.clear();
+    System.out.println(map); /* {} */
+  }
+}
