This Java Example shows how to get a Set of keys contained in HashMap using keySet method of Java HashMap class.
import java.util.Iterator; import java.util.HashMap; import java.util.Set; public class GetSetViewOfKeysFromHashMapExample { public static void main(String[] args) { // create object of HashMap HashMap phoneBook = new HashMap(); /** * Add key value pair to HashMap using Object put(Object key, Object * value) method of Java HashMap class, where key and value both are * objects put method returns Object which is either the value * previously tied to the key or null if no value mapped to the key. **/ phoneBook.put("John", "245745"); phoneBook.put("Joy", "245786"); phoneBook.put("Roy", "233783"); /** * Set keySet() - Returns a set view of the keys contained in this map. **/ Set nameSet = phoneBook.keySet(); System.out.println("Names in the phone book are :"); for (Object name : nameSet) { System.out.println("Name: " + name); } /** * Please note that resultant Set object is backed by the HashMap. Any * key that is removed from Set will also be removed from original * HashMap object. The same is not the case with the element addition. **/ // remove Roy from nameSet nameSet.remove("Roy"); // check if original HashMap still contains entry for name Roy. boolean blnExists = phoneBook.containsKey("Roy"); System.out.println("Does HashMap contain Roy ? " + blnExists); } }
The output is:
Names in the phone book are :
Name: Roy
Name: Joy
Name: John
Does HashMap contain Roy ? false
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