Java ArrayList

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 ArrayList:(Derived Data Type / Collections)


—> A normal Array have some limitations: 1.It can store same DataType                          elements/values, 2.It is Fixed Size.

—>To Overcome the above limitations we can use ArrayList Which can store multiple       DataType elements/values & it as no-Limit of Size.

—>An ArrayList is a predefined Class, So we can call Methods using Object.


*Note:  the name of the Object becomes the name of the ArrayList.


  • ArrayList Declaration: Two ways we can declare ArrayList 
    • To store any type of elements.   : ArrayList obj=new ArrayList();

       Example: ArrayList list = new ArrayList();

            

            2. To store same type of elements :

                ArrayList <Datatype> obj=new ArrayList <Datatype> ();

              Example: 1. ArrayList <String> list = new ArrayList <String>();//String type 

      2.ArrayList<Integer> list = new ArrayList <Integer>();//Number type


  • Adding Values to ArrayList: 
                To add values to ArrayList we use Method called “add()”

               Example: 1.ArrayList <String> obj = new ArrayList <String>();

  obj.add(“John”);  //adding string element to ArrayList. Duplicate                                                                 value also allowed.

   

               2.obj.add(index no, ”String”); // Syntax to insert element in specific                                                                                 location.

   obj.add(1, “Kakarla”); // Inserting element at index value :1


  • To know Size of an ArrayList:
        To Know the Size of an ArrayList we use Method called ”size()”.

         Example: System.out.println(obj.Size());



  • Remove an Element from ArrayList:
        To remove an element from ArrayList we use Method called ”remove()”.

        Example: obj.remove(index no); // It removes the element stored in that index                                                                   number.


  • Reading Values from ArrayList: There are Two ways 
             1.To list values separated by “,”  just give the object name in print statement.

                Example: System.out.println(obj);// It print all the elements present in the                                                                           ArrayList like: [value1,value2,value3]

             2.To list values individually we use Loop statements like “for loop”(enhanced                  for loop / for each loop). 

                Example: for(datatype variable: Name of ArrayList) //here the DataType                                         //Variable stores each value for every iteration of forLoop.

{

System.out.println(variable);// the variable contain the value 

}


*Note: the for loop will get error when ArrayList contain Multiple DataType Values, So              use  “Object”  as DataType for that variable in forLoop. In Java Object is a                    DataType which can support multiple DataType Values. We can use this for                any variables like: Object a; just like string a; but the Object DataType “a”

    can store multiple datatype values like: a=10; or a=raj; like this. Even a

            normal Array can store multiple datatype value by using Object datatype like: 

    Example: int a[ ]=new int a[5]; //can store only integer values 

    Object a[ ]= new object[5]; // can store multiple datatype values


    Example: for(Object variable: Name of ArrayList )                             {

System.out.println(variable);


    }

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