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

First, set the collection −String strArr[] = { "P", "Q", "R", "S" };Now, take a Set and add all the elements of the above collection using asList() method −Set s = new HashSet(Arrays.asList(strArr));The following is an example to add all elements from a collection to the 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

To remove all elements from a set, use the clear() method.Here is our set −HashSet set1 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat");Now, let us remove all the elements −set1.clear();The following is an example to remove all elements from a set −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       HashSet set1 = new HashSet ();       set1.add("Mat");       set1.add("Sat");       set1.add("Cat");       System.out.println("Set = "+ set1);       set1.clear();       System.out.println("Set after removing all the elements (blank) = ... Read More

To get the union of two sets, use the addAll() method.The first set −HashSet set1 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat");The second set −HashSet set2 = new HashSet (); set2.add("Mat"); set2.add("Cat"); set2.add("Fat"); set2.add("Hat");Get the union −set1.addAll(set2);The following is an example −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       HashSet set1 = new HashSet ();       HashSet set2 = new HashSet ();       set1.add("Mat");       set1.add("Sat");       set1.add("Cat");       System.out.println("Set1 = "+ set1);       set2.add("Mat"); ... Read More

All the elements of an ArrayList can be copied into an Object Array using the method java.util.ArrayList.toArray(). This method does not have any parameters and it returns an Object Array that contains all the elements of the ArrayList copied in the correct order.A program that demonstrates this is given as follows −Example Live Demoimport java.util.ArrayList; import java.util.List; public class Demo {    public static void main(String[] args) {       List aList = new ArrayList();       aList.add("Nathan");       aList.add("John");       aList.add("Susan");       aList.add("Betty");       aList.add("Peter");       Object[] objArr ... Read More

An ArrayList can be converted into an Array using the java.util.ArrayList.toArray() method. This method takes a single parameter i.e. the array of the required type into which the ArrayList elements are stored and it returns an Array that contains all the elements of the ArrayList in the correct order.A program that demonstrates this is given as follows −Example Live Demoimport java.util.ArrayList; import java.util.List; public class Demo {    public static void main(String[] args) {       List aList = new ArrayList();       aList.add("James");       aList.add("Harry");       aList.add("Susan");       aList.add("Emma");       ... Read More

To get the intersection of two sets, use the retainAll() method. Here are out two set −First set −HashSet set1 = new HashSet (); set1.add("Mat"); set1.add("Sat"); set1.add("Cat");Second set −HashSet set2 = new HashSet (); set2.add("Mat"); set2.add("Cat"); set2.add("Fat"); set2.add("Hat");Get the intersection −set1.retainAll(set2);The following is an example to get the intersection of two sets −Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       HashSet set1 = new HashSet ();       HashSet set2 = new HashSet ();       set1.add("Mat");       set1.add("Sat");       set1.add("Cat"); ... Read More

The location of an element in an ArrayList can be obtained using the method java.util.ArrayList.indexOf(). This method returns the index of the first occurrence of the element that is specified. If the element is not available in the ArrayList, then this method returns -1.A program that demonstrates this is given as follows −Example Live Demoimport java.util.ArrayList; import java.util.List; public class Demo {    public static void main(String[] args) {       List aList = new ArrayList();       aList.add("A");       aList.add("B");       aList.add("C");       aList.add("D");       aList.add("E");       System.out.println("The ... Read More