Prerequisite – ArrayList in Java
ArrayList in Java (equivalent to vector in C++) having dynamic size. It can be shrinked or expanded based on size. ArrayList is a part of 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
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 which is formed by 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.
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.
// Java program to illustrate customArraylist in Javaimport 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:
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