md file added

Author: preeti-14-7

lessons/arraylist.md

@@ -5,3 +5,184 @@ order: "4B"
 section: "Arrays"
 description: "learn arrays"
 ---
+ ## ArrayList in java 
+ <hr>
+ The ArrayList class is in implementation of the list interface that allow us to create resizable array. In simple term we can say that ArrayList in java is dynamic array for storing the elements.
+ It is just like the vector in c++.
+
+
+## Creating An ArrayList
+
+```java
+ ArrayList<type>arraylist = new ArrayList<> ; 
+ //here type define any type of ArrayList. 
+Example:
+   ArrayList<Integer> arrlist = new ArrayList<Integer>(n);
+
+```
+
+## Code Snippet to demonstrate the working of ArrayList in Java
+```java
+import java.io.*;
+import java.util.*;
+
+class ArrayListExample {
+	public static void main(String[] args)
+	{
+		//create array
+		ArrayList<Integer> arr = new ArrayList<Integer>(n);
+
+		arr.add(1);
+		arr.add(2);
+		arr.add(3);
+		arr.add(4);
+        System.out.println("List: " + arr );
+	}
+}
+
+```
+
+## Output
+```java
+List : [1, 2, 3, 4] 
+```
+ 
+## Methods OF ArrayList :
+Some Commonly used Methods
+
+  Method       |  Detail
+------------- | -------------
+size()        | give the size of the ArrayList
+sort()        | to sort the elements in the list
+isEmpty()	  | Checks if the arraylist is empty.
+indexOf()	  | to find index of any element.
+
+
+
+## Basic Operation in Java ArrayList :
+The ArrayList class have some methods to perform different operations on arraylists. Let's see some of most used methods.
+
+- Add elements
+- Access elements
+- Change elements
+- Remove elements
+
+## Add Elements :
+ - add() : This is the method to insert any elements at the end of the list.
+```java
+import java.util.ArrayList;
+
+class Main {
+  public static void main(String[] args){
+  
+    ArrayList<String> playerName = new ArrayList<>();
+
+    // add() method 
+    playerName.add("Virat");
+    playerName.add("Dhoni");
+    playerName.add("Sachin");
+	//print 
+    System.out.println("ArrayList: " + playerName);
+  }
+}
+```
+## Output
+```
+ArrayList : [Virat,Dhoni,Sachin]
+```
+
+- get() : This method is used to acess the elements from the list.
+
+```java
+import java.util.ArrayList;
+
+class Main {
+  public static void main(String[] args){
+    
+    ArrayList<String> playerName = new ArrayList<>();
+
+   
+    playerName.add("Virat");
+    playerName.add("Dhoni");
+    playerName.add("Sachin");
+    System.out.println("ArrayList: " + playerName);
+
+	// get() method
+    String name1 = playerName.get(1);
+    System.out.println(name1);
+  }
+}
+
+```
+## Output
+```
+ArrayList : [Virat,Dhoni,Sachin];
+Dhoni
+```
+- set(): This method is used to set any elements at any position.
+
+```java
+import java.util.ArrayList;
+
+class Main {
+  public static void main(String[] args) {
+    ArrayList<String> languages = new ArrayList<>();
+
+    // add() method without the index parameter
+    playerName.add("Virat");
+    playerName.add("Dhoni");
+    playerName.add("Sachin");
+    System.out.println("ArrayList: " + playerName);
+
+
+    // change the element of the array list
+    languages.set(2, "Rohit");
+    System.out.println("New ArrayList: " + playerName);
+  }
+}
+```
+## Output
+```
+ArrayList : [Virat,Dhoni,Sachin]
+New ArrayList : [Virat,Dhoni,Rohit]
+
+```
+- remove() : To remove the elements from the list
+
+```java
+import java.util.ArrayList;
+
+class Main {
+  public static void main(String[] args) {
+    ArrayList<String> animals = new ArrayList<>();
+
+
+    // add() method without the index parameter
+    playerName.add("Virat");
+    playerName.add("Dhoni");
+    playerName.add("Sachin");
+    System.out.println("ArrayList: " + playerName);
+
+    // remove element 
+    String name1 = playerName.remove(2);
+	//print list after removal
+    System.out.println("New ArrayList: " + playerName);
+	//removed elements
+    System.out.println("Removed: " + name1);
+  }
+}
+```
+## Output
+```
+ArrayList : [Virat,Dhoni,Sachin]
+New ArrayList : [Virat,Dhoni]
+Removed: Sachin
+```
+## Some remembering points about ArrayList
+
+- It comes under java.util package.
+- This class maintains insertion order.
+- It allows random access.
+- ArrayList is not Synchronized  
+- To convert ArrayList into an array we use toArray() method.
+- To converst array into an arraylist we use asList() method.