Java Articles

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Convert a Set into a List in Java

karthikeya Boyini
karthikeya Boyini
Updated on 11-Mar-2026 313 Views

First, create a Set and add elements −Set s = new HashSet(); s.add("P"); s.add(new Date()); s.add(new Long(898999)); s.add("Q"); s.add("R"); s.add(new Integer(1));Convert the above Set to a List −List l = new ArrayList(s);The following is an example to convert a set into a list in Java −Exampleimport java.util.ArrayList; import java.util.Date; import java.util.List; import java.util.Set; import java.util.HashSet; public class Demo {    public static void main(String[] args) {       Set s = new HashSet();       s.add("P");;       s.add(new Date());       s.add(new Long(898999));       s.add("Q");       s.add("R");       s.add(new ...

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Copy all the elements from one set to another in Java

Samual Sam
Samual Sam
Updated on 11-Mar-2026 1K+ Views

Use the clone() method to copy all elements from one set to another.First HashSet −HashSet set = new HashSet (); set.add("One"); set.add("Two");Create another set and clone first set into the second −HashSet newSet = new HashSet ();Copy (clone) all elements to the second set −newSet = (HashSet)set.clone();The following is an example to copy all elements from one set to another −Exampleimport java.util.*; public class Demo {    public static void main(String args[]) {       HashSet set = new HashSet ();       HashSet newSet = new HashSet ();       set.add("One");   ...

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Fetch key-valuepair from Java LinkedHashSet

karthikeya Boyini
karthikeya Boyini
Updated on 11-Mar-2026 372 Views

To fetch LinkedHashSet key-value pair in Java, use the entrySet() method.Let us first create LinkedHashSet and add some elements −LinkedHashMap l = new LinkedHashMap(); l.put("1", "Jack"); l.put("2", "Tom"); l.put("3", "Jimmy"); l.put("4", "Morgan"); l.put("5", "Tim"); l.put("6", "Brad");Now, fetch a key-value pair −l.entrySet()The following is an example to fetch key-value pair from LinkedHashSet −Exampleimport java.util.*; public class Demo {    public static void main(String[] args) {       LinkedHashMap l = new LinkedHashMap();       l.put("1", "Jack");       l.put("2", "Tom");       l.put("3", "Jimmy");       l.put("4", "Morgan");       l.put("5", "Tim");       ...

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Create a TreepMap in Java and add elements

Samual Sam
Samual Sam
Updated on 11-Mar-2026 99 Views

Let us create TreeMap in Java. It stores unique elements in ascending order −TreeMap m = new TreeMap();Now let us add some elements −m.put(1, "PHP"); m.put(2, "jQuery"); m.put(3, "JavaScript"); m.put(4, "Ruby"); m.put(5, "Java"); m.put(6, "AngularJS"); m.put(7, "ExpressJS");The following is an example to create a TreeMap −Exampleimport java.util.*; public class Demo {    public static void main(String args[]) {       TreeMap m = new TreeMap();       m.put(1, "PHP");       m.put(2, "jQuery");       m.put(3, "JavaScript");       m.put(4, "Ruby");       m.put(5, "Java");       m.put(6, "AngularJS");       m.put(7, ...

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Create a TreeMap in Java and add key-value pairs

karthikeya Boyini
karthikeya Boyini
Updated on 11-Mar-2026 1K+ Views

A TreeMap cannot contain duplicate keys. TreeMap cannot contain the null key. However, It can have null values.Let us first see how to create a TreeMap −TreeMap m = new TreeMap();Add some elements in the form of key-value pairs −m.put(1, "India"); m.put(2, "US"); m.put(3, "Australia"); m.put(4, "Netherlands"); m.put(5, "Canada");The following is an example to create a TreeMap and add key-value pairs −Exampleimport java.util.*; public class Demo {    public static void main(String args[]) {       TreeMap m = new TreeMap();       m.put(1, "India");       m.put(2, "US");       m.put(3, "Australia");       ...

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Java Program to remove a key from a TreeMap only if it is associated with a given value

karthikeya Boyini
karthikeya Boyini
Updated on 11-Mar-2026 206 Views

Use the remove() method to remove a key from a TreeMap only if it is associated with a given value. Let us first create a TreeMap and add some elements −TreeMap m = new TreeMap(); m.put(1, "India"); m.put(2, "US"); m.put(3, "Australia"); m.put(4, "Netherlands"); m.put(5, "Canada");To remove a key, set the key and the associated value here. If the associate value exists, then the key will get removed −m.remove(3, "Australia")The following is an example to remove a key from a TreeMap only if it is associated with a given value −Exampleimport java.util.*; public class Demo {    public static void main(String ...

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Get first entry from NavigableMap in Java

Samual Sam
Samual Sam
Updated on 11-Mar-2026 206 Views

To display first entry from NavigableMap in Java, use the firstEntry() method.Let us first create NavigableMap −NavigableMap n = new TreeMap(); n.put("A", 498); n.put("B", 389); n.put("C", 868); n.put("D", 988); n.put("E", 686); n.put("F", 888); n.put("G", 999); n.put("H", 444); n.put("I", 555); n.put("J", 666);Get the first entry now −n.firstEntry()The following is an example to get first entry from NavigableMap.Exampleimport java.util.*; public class Demo { public static void main(String[] args) { NavigableMap n = new TreeMap(); n.put("A", 498); n.put("B", 389); ...

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Create a Stack and Queue using ArrayDeque in Java

Samual Sam
Samual Sam
Updated on 11-Mar-2026 594 Views

Create a stack using ArrayDeque.Deque s = new ArrayDeque(); // stack s.push("Bat"); s.push("Mat"); s.push("Cat"); s.push("Rat"); s.push("Hat"); s.push("Fat");Create a queue using ArrayDeque −Deque q = new ArrayDeque(); // queue q.add("Bat"); q.add("Mat"); q.add("Cat"); q.add("Rat"); q.add("Hat"); q.add("Fat");The following is an example.Exampleimport java.util.ArrayDeque; import java.util.Deque; public class Demo {    public static void main(String args[]) {       Deque s = new ArrayDeque();       Deque q = new ArrayDeque();       // stack       s.push("Bat");       s.push("Mat");       s.push("Cat");       s.push("Rat");       s.push("Hat");       s.push("Fat");       ...

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Convert an ArrayList to HashSet in Java

Samual Sam
Samual Sam
Updated on 11-Mar-2026 1K+ Views

To convert ArrayList to HashSet, firstly create an ArrayList −List l = new ArrayList();Add elements to the ArrayList −l.add("Accent"); l.add("Speech"); l.add("Diction"); l.add("Tone"); l.add("Pronunciation");Now convert the ArrayList to HashSet −Set s = new HashSet(l);The following is an example to convert an ArrayList to HashSet in Java.Exampleimport java.util.ArrayList; import java.util.List; import java.util.Set; import java.util.HashSet; public class Main { public static void main(String[] args) { List l = new ArrayList(); l.add("Accent"); l.add("Speech"); l.add("Diction"); ...

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Get the first element from a Sorted Set in Java

Samual Sam
Samual Sam
Updated on 11-Mar-2026 638 Views

To create a Sorted Set, firstly create a Set.Set s = new HashSet();Add elements to the above set.int a[] = {77, 23, 4, 66, 99, 112, 45, 56, 39, 89}; Set s = new HashSet(); try { for(int i = 0; i < 5; i++) { s.add(a[i]); }After that, use TreeSet class to sort.TreeSet sorted = new TreeSet(s);Get the first element, using the first() method −System.out.println("First element of the sorted set = "+ (Integer)sorted.first());The following is the code to get the first element from a Sorted Set ...

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