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How Objects Can an ArrayList Hold in Java?

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  • Difficulty Level : Medium
  • Last Updated : 04 Oct, 2021
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ArrayList is a part of the collection framework and is present in java.util package. It provides us with dynamic arrays in Java just as Vector in C++. Though, it may be slower than standard arrays but can be helpful in programs where lots of manipulation in the array is needed.

In order to understand the problem is divided into two halves:

  1. First Half: Representing generic addition of a normal element in the ArrayList. Data-type of the elements that are to be stored in the ArrayList is either String or Integer type.
  2. Second half: Making the same ArrayList with class objects as elements.

Syntax: Declaring List 

ArrayList<String> names = new ArrayList<String>();

Here <String> represents the data-type of the elements that is to be stored in the ArrayList. Remember that this can not be any primitive data-type such as int or float.

Illustration: Sub Class taken for consideration is randomly named ‘Person’.

Method: List.get() method of List interface in Java is used to get the element present in this list at a given specific index.

  • Make an auxiliary java class.
  • Give it some properties. For example, class Person can include name, age, number, etc
  • Create a new object.
  • Store the above-created object inside the ArrayList.
  • Print elements of above object created using List.get() method.

Implementation: 

  • Making a Person class object.
  • Making an ArrayList with Person objects as elements.

(A) First Half: Representing generic addition of a normal element in the ArrayList.

Example

Java




// Java Program to add elements to List
 
// Importing ArrayList class from
// java.util package
import java.util.ArrayList;
 
// Class
public class GFG {
 
    // Mai driver method
    public static void main(String[] args)
    {
        // Creating an ArrayList object
        // (Declaring List of String type)
        ArrayList<String> names = new ArrayList<String>();
 
        // Adding (appending) elements to List
        // Custom inputs using add() method
        names.add("Computer");
        names.add("Science");
        names.add("Portal");
 
        // Printing all the elements of ArrayList
        // Declaring generic ArrayList of String type
        System.out.print(names);
    }
}


Output

[Computer, Science, Portal]

B) Second half: Making the same ArrayList with class objects as elements.

Example 

Java




// Java Program to show
// How objects can an ArrayList hold
 
// Importing ArrayList class from
// java.util package
import java.util.ArrayList;
 
// Class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
 
        // Make Person data-type objects
        Person p1 = new Person("Aditya", 19);
        Person p2 = new Person("Shivam", 19);
        Person p3 = new Person("Anuj", 15);
 
        // Create an ArrayList object
        //(Declaring List of Person type)
        ArrayList<Person> names = new ArrayList<Person>();
 
        // Adding objects to the ArrayList
        names.add(p1);
        names.add(p2);
        names.add(p3);
 
        // Print and display the elements of adobe ArrayList
        // using get() method
        System.out.println(names.get(0).name);
        System.out.println(names.get(0).age);
        System.out.println(names.get(1).name);
        System.out.println(names.get(1).age);
        System.out.println(names.get(2).name);
        System.out.println(names.get(2).age);
 
        // New Line
        System.out.println();
 
        // Optional Part for better understanding
        System.out.println(
            "Optional Part Added For Better Understanding");
 
        // (Optional)
        // Displaying what happens if printed by simply
        // passing List object as parameter
        System.out.println(names);
    }
}
 
// Class user-defined
class Person {
 
    // Random properties associated with the person
    // Person name
    String name;
    // Person age
    int age;
 
    // Constructor for class Person
    // for initializing objects
    Person(String name, int age)
    {
        // This keyword for efering to current object
        this.name = name;
        this.age = age;
    }
}


Output

Aditya
19
Shivam
19
Anuj
15

Optional Part Added For Better Understanding
[Person@214c265e, Person@448139f0, Person@7cca494b]

 
 

 


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