ArrayList of User-Defined Objects

Introduction

Since ArrayList supports generics, you can create an ArrayList of any data type. It can be of simple types such as Integer, String, or Double, or complex types such as an ArrayList of ArrayLists, an ArrayList of HashMaps, or an ArrayList of any user-defined objects.

Lab Objective

In the following lab, you will learn how to create an ArrayList of user-defined objects. We will utilize Arraylist, constructors, getters, and setters. This concept is very important for future lectures such as DAO, Hibernate, and Spring Boot. By the end of this lab, learners will be able to utilize the ArrayList of user-defined objects.

Instructions

Step 1

Create a new Java project and create a new Class named “Book,” and then add the code below in the Book class.

public class Book {
  private int number;
  private String name;
  private String author;
  private String category;

  // Constructor with arguments
  public Book(int number, String name, String author, String category) {
    this.name = name;
    this.category = category;
    this.author = author;
    this.number = number;
  }

  // Constructor without arguments
  public Book() {}

  public int getNumber() { return number; }

  public void setNumber(int number) { this.number = number; }

  public String getName1() { return name; }

  public void setName(String name1) { this.name = name1; }

  public String getAuthor() { return author; }

  public void setAuthor(String author) { this.author = author; }

  public String getCategory() { return category; }

  public void setCategory(String category) { this.category = category; }
}

The above is actually a POJO class for setter and getter.

Step 2

Create a new Class named “AddDataToArrayList,” and add the code below in the AddDataToArrayList class.

import java.util.ArrayList;
import java.util.Iterator;

public class AddDataToArrayList {
  public ArrayList<Book> bookdetails() {
    // User-defined class objects in Java ArrayList
    ArrayList<Book> list = new ArrayList<Book>();

    // Passing data using Constructors
    Book b1 = new Book(1, "Death note", "John", "cartoon");
    Book b2 = new Book(2, "Stranger Things", "brothers", "suspense");
    Book b3 = new Book(3, "Spider man", "Alex", "Kids");
    Book b4 = new Book(4, "GentleMen", "Max", "Action");

    // Passing data using setter
    Book b5 = new Book();
    b5.setNumber(5);
    b5.setName("Java FullStack");
    b5.setAuthor("Flex");
    b5.setCategory("Programming");

    // Adding Books objects to Arraylist
    list.add(b1);
    list.add(b2);
    list.add(b3);
    list.add(b4);
    list.add(b5);

    return list;
  }
}

In the above class, as a demonstration, we are passing Data to Book class by using the constructor and by using the setter method.

Step 3

Create a new Class named “showData,” and add the code below in the showData class.

import java.util.ArrayList;
import java.util.Iterator;

public class showData {
  public static void main(String[] args) {
    // instantiation to class AddDataToArrayList
    AddDataToArrayList b = new AddDataToArrayList();
    ArrayList<Book> mybooklist = b.bookdetails();

    for(Book showValue: mybooklist) {
      // invoking getter method for getting Data
      System.out.println(showValue.getNumber() + " " + showValue.getName() +" "+ showValue.getCategory() +" "+ showValue.getAuthor());
    }
  }
}

Output:

1 Death note cartoon John
2 Stranger Things suspense brothers
3 Spider man Kids Alex
4 GentleMen Action Max
5 Java FullStack Programming Flex

2KB

GLAB - 303.11.3 - ArrayList of User-Defined Objects.zip

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