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Simple Java HashMap example

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  1. /*
  2.   Simple Java HashMap example
  3.   This simple Java Example shows how to use Java HashMap. It also describes how to
  4.   add something to HashMap and how to retrieve the value added from HashMap.
  5. */
  6.  
  7. import java.util.HashMap;
  8.  
  9. public class JavaHashMapExample {
  10.  
  11.   public static void main(String[] args) {
  12.    
  13.     //create object of HashMap
  14.     HashMap hMap = new HashMap();
  15.    
  16.     /*
  17.       Add key value pair to HashMap using
  18.       Object put(Object key, Object value) method of Java HashMap class,
  19.       where key and value both are objects
  20.       put method returns Object which is either the value previously tied
  21.       to the key or null if no value mapped to the key.
  22.     */
  23.    
  24.     hMap.put("One", new Integer(1));
  25.     hMap.put("Two", new Integer(2));
  26.    
  27.     /*
  28.       Please note that put method accepts Objects. Java Primitive values CAN NOT
  29.       be added directly to HashMap. It must be converted to corrosponding
  30.       wrapper class first.
  31.     */
  32.    
  33.     //retrieve value using Object get(Object key) method of Java HashMap class
  34.     Object obj = hMap.get("One");
  35.     System.out.println(obj);  
  36.    
  37.     /*
  38.       Please note that the return type of get method is an Object. The value must
  39.       be casted to the original class.
  40.     */
  41.  
  42.    
  43.   }
  44. }
  45. /*
  46. Output of the program would be
  47. 1
  48. */