Custom ArrayList in Java

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ArrayList in Java
ArrayList in Java (equivalent to vector in C++) having a dynamic size. It can be shrunk or expanded based on size. ArrayList is a part of the collection framework and is present in java.util package.
An ArrayList:

ArrayList <E> list = new ArrayList <> ();

E here represents an object datatype e.g. Integer. The Integer class wraps a value of the primitive type int in an object. An object of type Integer contains a single field whose type is int.
More about Integer Object: here
list
Custom ArrayList: A custom ArrayList has attributes based on user requirements and can have more than one type of data. This data is provided by a custom inner class that is formed by a combination of various primitive object datatypes.

Consider a case when we have to take input as N number of students and details are:
roll number, name, marks, phone number
A normal method using object ArrayList would be:

   // define 4 ArrayLists and save data accordingly in
   // each of them.
    
   // roll number arraylist
   ArrayList<Integer> roll = new ArrayList<>(); 

   // name arraylist
   ArrayList<String> name = new ArrayList<>();

   // marks arraylist
   ArrayList<Integer> marks = new ArrayList<>();

   // phone number arraylist
   ArrayList<Long> phone = new ArrayList<>();

   // and for n students
   for(int i = 0; i < n; i++)
   {
     // add all the values to each arraylist 
     // each arraylist has primitive datatypes
     roll.add(rollnum_i);
     name.add(name_i);
     marks.add(marks_i);
     phone.add(phone_i);
  }

Now using a custom Arraylist:
The custom ArrayList simply supports multiple data in the way as shown in this image.
custom
To construct Custom ArrayList

Build an ArrayList Object and place its type as a Class Data.
Define a class and put the required entities in the constructor.
Link those entities to global variables.
Data received from the ArrayList is of that class type which stores multiple data.

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// Java program to illustrate customArraylist in Java

import java.util.ArrayList;

class CustomArrayList

{

// custom class which has data type

// class has defined the type of data ArrayList

// size of input 4

int n=4;

// the custom datatype class

class Data

{

// global variables of the class

int roll;

String name;

int marks;

long phone;

// constructor has type of data that is required

Data(int roll, String name, int marks, long phone)

{

// initialize the input variable from main

// function to the global variable of the class

this.roll = roll;

this.name = name;

this.marks = marks;

this.phone = phone;

}

public static void main(String args[])

{

// suppose the custom input data

int roll[] = {1, 2, 3, 4};

String name[] = {"Shubham", "Atul", "Ayush", "Rupesh"};

int marks[] = {100, 99, 93, 94};

long phone[] = {8762357381L, 8762357382L, 8762357383L,

8762357384L

};

// Create an object of the class

CustomArrayList custom = new CustomArrayList();

// and call the function to add the values to the arraylist

custom.addValues(roll, name, marks, phone);

}

public void addValues(int roll[], String name[], int marks[],

long phone[])

{

// local custom arraylist of data type

// Data having (int, String, int, long) type

// from the class

ArrayList<Data> list=new ArrayList<>();

for (int i = 0; i < n; i++)

{

// create an object and send values to the

// constructor to be saved in the Data class

list.add(new Data(roll[i], name[i], marks[i],

phone[i]));

}

// after adding values printing the values to test

// the custom arraylist

printValues(list);

}

public void printValues(ArrayList<Data> list)

{

// list- the custom arraylist is sent from

// previous function

for (int i = 0; i < n; i++)

{

// the data received from arraylist is of Data type

// which is custom (int, String, int, long)

// based on class Data

Data data = list.get(i);

// data variable of type Data has four primitive datatypes

// roll -int

// name- String

// marks- int

// phone- long

System.out.println(data.roll+" "+data.name+" "

+data.marks+" "+data.phone);

}

Output:

1 Shubham 100 8762357381
2 Atul 99 8762357382
3 Ayush 93 8762357383
4 Rupesh 94 8762357384

References:

Oracle documentation
ArrayLists

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