Arrays of Objects in Java

In Java, you can create arrays not only for primitive types (like int, double) but also for objects, including user-defined classes. Arrays of objects are widely used to store multiple instances of a class in a single container, making data management efficient.

Why Use Arrays of Objects?

Organize related objects in a single container.
Efficient for storing multiple user-defined types.
Useful in real-world applications, such as:
- School management → array of Student objects.
- Employee management → array of Employee objects.
- Inventory systems → array of Product objects.

Declaring and Creating Arrays of Objects

Step 1: Declare the Array

Student[] students; // Declares an array of Student objects

Step 2: Allocate Memory

students = new Student[3]; // Array can hold 3 Student references

At this point, students[0], students[1], students[2] are null because no objects have been created yet.

Step 3: Initialize Objects

class Student {
    int id;
    String name;

    Student(int id, String name) {
        this.id = id;
        this.name = name;
    }

    void display() {
        System.out.println(id + " " + name);
    }
}

public class ArrayOfObjectsExample {
    public static void main(String[] args) {
        Student[] students = new Student[3];

        students[0] = new Student(1, "Aman");
        students[1] = new Student(2, "Neha");
        students[2] = new Student(3, "Ravi");

        for (Student s : students) {
            s.display();
        }
    }
}

Output:

1 Aman
2 Neha
3 Ravi

Points to Remember

Arrays store references, not the actual objects.
Always instantiate each object before use to avoid NullPointerException.
Use array.length to get the number of object references.
Arrays of objects can be multidimensional:

Student[][] classes = new Student[2][3];

For-each loop provides clean iteration syntax:

for (Student s : students) {
    s.display();
}

Polymorphism with Arrays of Objects

You can store subclass objects in a superclass array:

class Animal { void sound() { System.out.println("Some sound"); } }
class Dog extends Animal { void sound() { System.out.println("Woof"); } }
class Cat extends Animal { void sound() { System.out.println("Meow"); } }

public class PolymorphismArrayExample {
    public static void main(String[] args) {
        Animal[] animals = new Animal[2];
        animals[0] = new Dog();
        animals[1] = new Cat();

        for (Animal a : animals) {
            a.sound(); // Runtime polymorphism
        }
    }
}