ArrayList in Java
Class ArrayList is a part of Java Collection Framework which extends AbstractClass and implements List Interface. Class ArrayList is a resizable array and it is found in the java.util package. Class ArrayList is a generic class and its uses as Class ArrayList <E>.What is the difference between array and ArrayList in java?
The array is a fixed size and it cannot be
modified but ArrayList is dynamic in nature, it can grow and shrink.
Java Array is not a generic type whereas ArrayList is a
generic type (Generic data types works with “any” data type). Java ArrayList
class is none synchronized.
Java array can contain be both primitives data type and
objects but ArrayList can contain only object elements.
By assignment operator data store in array but in ArrayList
data entry with the help of add() method.
Java ArrayList Constructors
public ArrayList(): Most widely used Java ArrayList
constructor. This ArrayList constructor will return ArrayList() Constructs an
empty list.
ArrayList(Collection<? extends E> c) Constructs a list
containing the elements of the specified collection, in the order they are
returned by the collection's iterator.
ArrayList(int initialCapacity) Constructs an empty list with
the specified initial capacity. The capacity is the size of the underlying array.
Adding/Inserting String elements in ArrayList
import java.util.ArrayList;
public class School {
public static void
main(String[] args) {
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.add("Shakil");
student.add("Shakil");
student.add("Shakil");
System.out.println(student);
}
}
Output:
[Amit, Sunil, Akbar, Shakil, Shakil, Kapil]
Adding/Inserting Integer elements in ArrayList
import java.util.*;
public class IntegerArrayList {
public static void
main(String []args)
{
//Declaring
ArrayList in integer
ArrayList<Integer> intArrayList = new ArrayList<Integer>();
intArrayList.add
(5);
intArrayList.add
(2);
intArrayList.add
(7);
intArrayList.add
(8);
intArrayList.add
(9);
//Displaying
array list
for (int i :
intArrayList) {
System.out.println("The ArrayList item: " + i);
}
}
}
Output
The ArrayList item: 5
The ArrayList item: 2
The ArrayList item: 7
The ArrayList item: 8
The ArrayList item: 9
Change the elements of specified position
To change or modify an element, we use the
set () method and refer to the index number:
import java.util.ArrayList;
public class School {
public static void
main(String[] args) {
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.add("Shakil");
student.add(1,"Uma");
student.add("Kapil");
System.out.println(student);
}
}
Output
[Amit, Uma, Sunil, Akbar, Shakil, Kapil]
How to remove elements from the ArrayList?
Import java.util.ArrayList;
public class School {
public static void
main(String[] args) {
ArrayList<String> student = new ArrayList<String>();
student.add(“Amit”);
student.add(“Sunil”);
student.add(“Akbar”);
student.remove(“Shakil”);
student.remove(1);
student.add(“Uma”);
student.add(“Kapil”);
System.out.println(student);
}
}
Output:
[Amit, Akbar, Uma, Kapil]
Here element “Shakil” and “Sunil” have been deleted.
How to find the size of an ArrayList?
Using size () method
we can find the size of an ArrayList.
import java.util.ArrayList;
public class School {
public static void
main(String[] args) {
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.remove("Shakil");
student.add("Uma");
student.add("Kapil");
System.out.println(student.size());
}
}
Output:
5
How to display ArrayList elements through the loop?
With for Loop
import java.util.ArrayList;
public class School {
public static void
main(String[] args)
{
int i;
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.remove("Shakil");
student.add("Uma");
student.add("Kapil");
// Elements
display through for loop
for (i = 0; i
< student.size(); i++) {
System.out.println(student.get(i));
}
}
}
Output:
Amit
Sunil
Akbar
Uma
Kapil
With for each Loop
import java.util.ArrayList;
public class School {
public static void
main(String[] args)
{
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.remove("Shakil");
student.add("Uma");
student.add("Kapil");
// Elements
display through for each loop
for (String i
: student) {
System.out.println(i);
}
}
}
How to sort an ArrayList element?
ArrayList elements can be sort with another sort() method
which is in Collection class of java.util package.
import java.util.ArrayList;
import java.util.Collections;
public class School {
public static void
main(String[] args)
{
ArrayList<String> student = new ArrayList<String>();
student.add("Amit");
student.add("Sunil");
student.add("Akbar");
student.remove("Shakil");
student.add("Uma");
student.add("Kapil");
// Elements
display in sort order
Collections.sort(student); //
for (String i
: student) {
System.out.println(i);
}
}
}
Output
Akbar
Amit
Kapil
Sunil
Uma
Search in ArrayList java
We can
search in ArrayList element by contains method. When we search an element in
ArrayList, it will return true if found and return false if not found.
import java.util.*;
public class ArrayListSearch {
public static void
main(String []args)
{
Scanner sc =
new Scanner(System.in);
//Declaring
ArrayList
ArrayList<String> student = new ArrayList<String>();
student.add ("Shami");
student.add
("Virat");
student.add
("Dhoni");
student.add
("Vijay");
student.add
("Amir");
student.add
("Akbar");
student.add
("Ajay");
System.out.println(student);
System.out.println("Enter a name to search: ");
String
searchName = sc.nextLine();
if
(student.contains(searchName)){
System.out.println("The name is found!");
}
else
{
System.out.println("The name does not exist!");
}
}
}
Output:
[Shami, Virat, Dhoni, Vijay, Amir, Akbar, Ajay]
Enter a name to search:
Dhoni
The name is found!
[Shami, Virat, Dhoni, Vijay, Amir, Akbar, Ajay]
Enter a name to search:
Nikhil
The name does not exist!
How to merge two ArrayLists in Java?
With the help of addAll() method we can add or merge two
ArrayList into one.
import java.util.ArrayList;
import java.util.Arrays;
public class MergeArrayList
{
public static void
main(String[] args) throws Exception
{
// First
ArrayList
ArrayList<String> student1 = new ArrayList<String>();
student1.add
("Shami");
student1.add
("Virat");
student1.add
("Dhoni");
student1.add
("Vijay");
student1.add
("Amir");
student1.add
("Ajay");
System.out.println ("First ArrayList");
System.out.println (student1);
// Second
ArrayList
ArrayList<String> student2 = new ArrayList<String>();
student2.add
("Amit");
student2.add
("Sunil");
student2.add
("Akbar");
student2.add("Uma");
student2.add("Kapil");
System.out.println("Second ArrayList");
System.out.println(student2);
// Merge both
lists
student1.addAll(student2);
// After
Merging of two array
System.out.println("After Merging of two array");
System.out.println(student1);
}
}
Output:
First ArrayList
[Shami, Virat, Dhoni, Vijay, Amir, Ajay]
Second ArrayList
[Amit, Sunil, Akbar, Uma, Kapil]
After Merging of two array
[Shami, Virat, Dhoni, Vijay, Amir, Ajay, Amit, Sunil, Akbar,
Uma, Kapil]
Merge two ArrayList without duplicates
With the help of LinkedHashSet, we can merge two
ArrayList without duplicate values. It will also intake the order.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
public class MergeArrayListNoDuplicate
{
public static void main(String[]
args) throws Exception
{
ArrayList<Integer>
arrayList1 = new ArrayList<>(Arrays.asList(1, 3, 4, 5, 7, 8));
ArrayList<Integer>
arrayList2 = new ArrayList<>(Arrays.asList(11, 22, 4, 33, 55));
System.out.println("First ArrayList :" + arrayList1);
System.out.println("Second ArrayList:" + arrayList2);
Set<Integer> hashSet
= new LinkedHashSet<>(arrayList1);
hashSet.addAll(arrayList2);
List<Integer>
mergeList = new ArrayList<>(hashSet);
System.out.println("Merge ArrayList
:" + mergeList);
}
}
Output:
First ArrayList :[1, 3, 4, 5, 7, 8]
Second ArrayList:[11, 22, 4, 33, 55]
Merge ArrayList :[1, 3, 4, 5, 7, 8, 11, 22, 33, 55]
How do you convert an ArrayList to Array?
Converting ArrayList to the array we can use toArray() method,
and it will return an array with all elements of ArrayList.
import java.util.ArrayList;
import java.util.Arrays;
public class ArrayListToArray
{
public static void
main(String[] args) throws Exception
{
ArrayList<Integer> arrayList = new
ArrayList<>(Arrays.asList(1, 3, 4, 5, 7, 8));
Object[] array
= arrayList.toArray();
//Printing the
elements of the array.
for (Object ob
: array)
{
System.out.print(ob
+ " ");
}
}
}
Output:
1 3 4 5 7 8
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