To count the number of elements in a HashSet, use the size() method.Create HashSet −String strArr[] = { "P", "Q", "R" }; Set s = new HashSet(Arrays.asList(strArr));Let us now count the number of elements in the above Set −s.size()The following is an example to count the number of elements in a HashSet −Example Live Demoimport java.util.Arrays; import java.util.HashSet; import java.util.Set; public class Demo {    public static void main(String[] a) {       String strArr[] = { "P", "Q", "R" };       Set s = new HashSet(Arrays.asList(strArr));       System.out.println("Elements: "+s);       System.out.println("Number of Elements: ... Read More

Check whether a Map is empty or not using the isEmpty() method.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, use the following method to check whether the Map is empty or not. Since we added some elements above, therefore the Map is not empty −n. isEmpty();The following is an example to implement isEmpty() method −Example Live Demoimport java.util.*; public class Demo {    public static void main(String[] args) {       NavigableMap n = new ... Read More

Clear the NavigableMap in Java, using the clear() method.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, use the clear() method −n.clear();The following is an example to implement clear() method and clear the NavigableMap −Example Live Demoimport java.util.*; public class Demo {    public static void main(String[] args) {       NavigableMap n = new TreeMap();       n.put(5, "Tom");       n.put(9, "John");       n.put(14, "Jamie");       n.put(1, "Tim"); ... Read More

Create an array and convert it to List −Integer[] arr = { 10, 15, 20, 10, 10, 10, 20, 30, 35, 40, 40}; List l = Arrays.asList(arr);Now, let us convert the above array to HashSet −Set s = new HashSet(l);The following is an example to convert array to HashSet −Example Live Demoimport java.util.*; public class Demo {    public static void main(String[] argv) throws Exception {       Integer[] arr = { 10, 15, 20, 10, 10, 10, 20, 30, 35, 40, 40};       List l = Arrays.asList(arr);       Set s = new HashSet(l);       for (Iterator i = s.iterator(); i.hasNext();) {          Object ele = i.next();          System.out.println(ele);       }    } }Output35 20 40 10 30 15

Declare a HashSet and add elements −Set hs = new HashSet(); hs.add(20); hs.add(39); hs.add(67); hs.add(79);Now, iterate over the elements −for (Iterator i = hs.iterator(); i.hasNext();) {    Object ele = i.next();    System.out.println(ele); }The following is an example that iterate over the elements of HashSet −Example Live Demoimport java.util.HashSet; import java.util.Iterator; import java.util.Set; public class Demo {    public static void main(String[] argv) throws Exception {       Set hs = new HashSet();       hs.add(20);       hs.add(39);       hs.add(67);       hs.add(79);       System.out.println("Elements = ");       for (Iterator ... Read More

To remove specified element from HashSet, use the remove() method.First, declare a HashSet and add elements −Set hs = new HashSet(); hs.add(20); hs.add(39); hs.add(67); hs.add(79); hs.add(81); hs.add(87); hs.add(88);Let’s say you need to remove element 39. For that, use the remove() method −hs.remove(39);The following is an example to remove specified element from HashSet −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       Set hs = new HashSet();       hs.add(20);       hs.add(39);       hs.add(67);       hs.add(79);       hs.add(81);       hs.add(87);     ... Read More

Create a HashSet and add elements to it −Set hs = new HashSet(); hs.add(20); hs.add(39); hs.add(67); hs.add(79); hs.add(81); hs.add(87);Try the below given code to iterate through the elements −Iterator i = hs.iterator(); while (i.hasNext()) System.out.println(i.next());To iterate through the elements of HashSet, try the following code −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       Set hs = new HashSet();       hs.add(20);       hs.add(39);       hs.add(67);       hs.add(79);       hs.add(81);       hs.add(87);       hs.add(88);       System.out.println("Elements = ... Read More

To get the size of HashSet, use the size() method. Let us create a HashSet and add elements −Set hs = new HashSet(); hs.add(15); hs.add(71); hs.add(82); hs.add(89); hs.add(91);Let us now use size() and get the size of HashSet −hs.size()The following is an example to get the size of HashSet −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       Set hs = new HashSet();       hs.add(15);       hs.add(71);       hs.add(82);       hs.add(89);       hs.add(91);       System.out.println("Elements = "+hs);       ... Read More

Declare a HashSet and add elements −Set hs = new HashSet(); hs.add(15); hs.add(71); hs.add(82); hs.add(89); hs.add(91); hs.add(93); hs.add(97); hs.add(99);To copy all the elements, use the toArray() method −Object[] obArr = hs.toArray();The following is an example to copy all elements to HashSet to an object array −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       Set hs = new HashSet();       hs.add(15);       hs.add(71);       hs.add(82);       hs.add(89);       hs.add(91);       hs.add(93);       hs.add(97);       hs.add(99);   ... Read More

To remove all the elements from HashSet, use the clear() method.Create a HashSet and initialize elements −String strArr[] = { "P", "Q", "R", "S" }; Set s = new HashSet(Arrays.asList(strArr));Now, to remove all the above elements −s.clear()The following is an example to remove all elements from a HashSet −Example Live Demoimport java.util.Arrays; import java.util.HashSet; import java.util.Set; public class Demo {    public static void main(String[] a) {       String strArr[] = { "P", "Q", "R", "S" };       Set s = new HashSet(Arrays.asList(strArr));       strArr = new String[] { "R", "S", "T", "U" };   ... Read More