The previous index and next index in an ArrayList can be obtained using the methods previousIndex() and nextIndex() respectively in the ListIterator Interface.The previousIndex() method returns the index of the element that is returned by the previous() method while the nextIndex() method returns the index of the element that is returned by the next() method. Neither of these methods require any parameters.A program that demonstrates this is given as followsExample Live Demoimport java.util.ArrayList; import java.util.ListIterator; public class Demo {    public static void main(String[] args) {       ArrayList aList = new ArrayList();       aList.add("Amy");       ... Read More

A ListIterator can be used to traverse the elements in the forward direction as well as the reverse direction in a LinkedList. The method hasPrevious( ) in ListIterator returns true if there are more elements in the LinkedList while traversing in the reverse direction and false otherwise. The method previous( ) returns the previous element in the LinkedList and reduces the cursor position backward.A program that demonstrates this is given as follows.Example Live Demoimport java.util.LinkedList; import java.util.List; import java.util.ListIterator; public class Demo {    public static void main(String[] args) {       List l = new LinkedList();       ... Read More

A specific element in the LinkedList can be removed using the java.util.LinkedList.remove() method. This method removes the specified element the first time it occurs in the LinkedList and if the element is not in the LinkedList then no change occurs. The parameter required for the LinkedList.remove() method is the element to be removed.A program that demonstrates this is given as follows.Example Live Demoimport java.util.LinkedList; public class Demo {    public static void main(String[] args) {       LinkedList l = new LinkedList();       l.add("Apple");       l.add("Mango");       l.add("Pear");       l.add("Orange");     ... Read More

A Set is a generic set of values with no duplicate elements. A TreeSet is a set where the elements are sorted.A HashSet is a set where the elements are not sorted or ordered. It is faster than a TreeSet. The HashSet is an implementation of a Set.Set is a parent interface of all set classes like TreeSet, HashSet, etc.Example Live Demoimport java.util.*; public class Demo {    public static void main(String args[]) {       int a[] = {77, 23, 4, 66, 99, 112, 45, 56, 39, 89};       Set s = new HashSet();       ... Read More

First, create a HashMap and add elementsHashMap hm = new HashMap(); hm.put("Wallet", new Integer(700)); hm.put("Belt", new Integer(600)); hm.put("Backpack", new Integer(1200));Now, retrieve all the keysSet keys = hm.keySet(); System.out.println("Keys..."); Iterator i = keys.iterator(); while (i.hasNext()) {    System.out.println(i.next()); }The following is an example to get the set of all key in HashMapExample Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create hash map HashMap hm = new HashMap(); hm.put("Wallet", new Integer(700)); ... Read More

To remove all values from HashMap, use the clear() method.First, let us create a HashMap.HashMap hm = new HashMap();Add some elements to the HashMaphm.put("Wallet", new Integer(700)); hm.put("Belt", new Integer(600)); hm.put("Backpack", new Integer(1200));Now, remove all the elementshm.clear();The following is an example to remove all values from HashMap.Example Live Demoimport java.util.*; public class Demo { public static void main(String args[]) { // Create hash map HashMap hm = new HashMap(); hm.put("Wallet", new Integer(700)); hm.put("Belt", new Integer(600)); ... Read More

An LinkedList can be cleared in Java using the method java.util.LinkedList.clear(). This method removes all the elements in the LinkedList. There are no parameters required by the LinkedList.clear() method and it returns no value.A program that demonstrates this is given as follows.Example Live Demoimport java.util.LinkedList; public class Demo { public static void main(String[] args) { LinkedList l = new LinkedList(); l.add("Orange"); l.add("Apple"); l.add("Peach"); l.add("Guava"); ... Read More

The last index of a particular element in an ArrayList can be obtained by using the method java.util.ArrayList.lastIndexOf(). This method returns the index of the last occurance 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("Orange");       aList.add("Apple");       aList.add("Peach");       aList.add("Orange");       aList.add("Mango");     ... Read More

The index of a particular element in an ArrayList can be obtained by 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("Orange");       aList.add("Apple");       aList.add("Peach");       aList.add("Guava");       aList.add("Mango");       ... Read More

The pollFirstEntry() method in NavigableMap remove and return a key-value mapping associated with the least key in this mapThe following is an example to implement pollFirstEntry() methodExample 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"); n.put(4, "Jackie"); n.put(15, ... Read More