To create a HashMap, use the HashMap class −HashMap hm = new HashMap();Add elements to the HashMap in the form of key-value pair −hm.put("Bag", new Integer(1100)); hm.put("Wallet", new Integer(700)); hm.put("Belt", new Integer(600));The following is an example to create HashMap and add key-value pair −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       // Create a hash map       HashMap hm = new HashMap();       // Put elements to the map       hm.put("Bag", new Integer(1100));       hm.put("Wallet", new Integer(700));       hm.put("Belt", new Integer(600)); ... Read More

Create a HashMap −HashMap hm = new HashMap();Add elements to the HashMap that we will be displaying afterward −hm.put("Maths", new Integer(98)); hm.put("Science", new Integer(90)); hm.put("English", new Integer(97)); hm.put("Physics", new Integer(91));Now, to display the HashMap elements, use Iterator. The following is an example to display HashMap elements −Example Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create a hash map HashMap hm = new HashMap(); // Put elements to the map ... Read More

Use the size() method to get the count of elements.Let us first create a HashMap and add elements −HashMap hm = new HashMap(); // Put elements to the map hm.put("Maths", new Integer(98)); hm.put("Science", new Integer(90)); hm.put("English", new Integer(97));Now, get the size −hm.size()The following is an example to get the count of HashMap elements −Example Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create a hash map HashMap hm = new HashMap(); // Put elements ... Read More

To add elements to HashMap, use the put() method.First, create a HashMap −HashMap hm = new HashMap();Now, let us add some elements to the HashMap −hm.put("Maths", new Integer(98)); hm.put("Science", new Integer(90)); hm.put("English", new Integer(97));The following is an example to add elements to HashMap −Example Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create a hash map HashMap hm = new HashMap(); // Put elements to the map hm.put("Maths", ... Read More

To retrieve the set of keys from HashMap, use the keyset() method. However, for set of values, use the values() method.Create a HashMap −HashMap hm = new HashMap(); hm.put("Wallet", new Integer(700)); hm.put("Belt", new Integer(600)); hm.put("Backpack", new Integer(1200));Now, retrieve the keys −Set keys = hm.keySet(); Iterator i = keys.iterator(); while (i.hasNext()) { System.out.println(i.next()); }Retrieve the values −Collection getValues = hm.values(); i = getValues.iterator(); while (i.hasNext()) { System.out.println(i.next()); }The following is an example to get the set of all keys and values in HashMap −Example Live Demoimport java.util.*; public class Demo { public static ... Read More

To create a HashMap, use the HashMap map and new −HashMap hm = new HashMap();Now, set elements −hm.put("Finance", new Double(999.87)); hm.put("Operations", new Double(298.64)); hm.put("Marketing", new Double(39.56));Display the elements now using the following code −Example Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create a hash map HashMap hm = new HashMap(); // Put elements to the map hm.put("Finance", new Double(999.87)); hm.put("Operations", new ... Read More

To get the size of NavigableMap, use the size() method. It returns the count of elements in the NavigableMap.Let us first create a NavigableMap and add some elements to it −NavigableMap n = new TreeMap(); n.put(5, "Tom"); n.put(9, "John"); n.put(14, "Jamie"); n.put(1, "Tim"); n.put(4, "Jackie"); n.put(15, "Kurt"); n.put(19, "Tiger"); n.put(24, "Jacob");Now, get the size −n.size();The following is an example to implement the size() method to get the size of the NavigableMap −Example Live Demoimport java.util.*; public class Demo { public static void main(String[] args) { NavigableMap n = new TreeMap(); ... Read More

The NavigableMap lastEntry() method returns a key-value mapping associated with the greatest key in this map.Let us first create a NavigableMap and add some elements to it −NavigableMap n = new TreeMap(); n.put(5, "Tom"); n.put(9, "John"); n.put(14, "Jamie"); n.put(1, "Tim"); n.put(4, "Jackie"); n.put(15, "Kurt"); n.put(19, "Tiger"); n.put(24, "Jacob");Now, get the last entry −n.lastEntry();The following is another example to get last entry from NavigableMap −Example Live Demoimport java.util.*; public class Demo { public static void main(String[] args) { NavigableMap n = new TreeMap(); n.put("A", 498); ... Read More

First, use the getenv() method to get the environment variables −System.out.println("PATH = " + System.getenv("PATH"));Now, get the key and value. Loop through to get the list of environment variables −Map e = System.getenv(); for (Iterator i = e.entrySet().iterator(); i.hasNext();) { Map.Entry mapEntry = (Map.Entry) i.next(); System.out.println(mapEntry.getKey() + " = " + mapEntry.getValue()); }The following is an example to retrieve environment variables with Map Collection −Example Live Demoimport java.util.Iterator; import java.util.Map; public class Demo { public static void main(String args[]) { System.out.println("PATH = " + System.getenv("PATH")); ... Read More

Use the subset() method to get elements from a limit. At first, create NavigableSet and add elements −NavigableSet set = new TreeSet(); set.add(10); set.add(25); set.add(40); set.add(55); set.add(70); set.add(85);Now, use the subset() method −set.subSet(40, 85)The following is an example to implement subset() method of Java NaviagbleSet class −Example Live Demoimport java.util.NavigableSet; import java.util.TreeSet; public class Demo { public static void main(String[] args) { NavigableSet set = new TreeSet(); set.add(10); set.add(25); set.add(40); set.add(55); set.add(70); set.add(85); set.add(100); System.out.println("Returned Value = " + set.subSet(40, 85)); } }OutputReturned Value = [40, 55, 70]