02.Types of Objects in Java

Types of Objects in Java. Objects are instances of classes, but they can be categorized based on how they are created, their lifecycle, and behavior.

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1. Regular / Normal Object

• Definition: Standard object created using the new keyword.

• Characteristics: Stored in heap memory; can have multiple instances.

• Example:

class Car {
    String brand;
}
public class Main {
    public static void main(String[] args) {
        Car c1 = new Car(); // Regular object
        Car c2 = new Car();
    }
}

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2. Anonymous Object

• Definition: Object without a reference variable; used when the object is needed only once.

• Characteristics: Cannot be reused; often used in method calls.

• Example:

class Car {
    void drive() {
        System.out.println("Driving...");
    }
}
public class Main {
    public static void main(String[] args) {
        new Car().drive(); // Anonymous object
    }
}

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3. Singleton Object

• Definition: Only one instance of the class exists in the application.

• Characteristics: Used for resource management, logging, configuration.

• Example:

class Singleton {
    private static Singleton instance;
    private Singleton() {}
    public static Singleton getInstance() {
        if(instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}
public class Main {
    public static void main(String[] args) {
        Singleton s1 = Singleton.getInstance();
        Singleton s2 = Singleton.getInstance();
        System.out.println(s1 == s2); // true
    }
}

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4. Immutable Object

• Definition: Object whose state cannot change after creation.

• Characteristics: Thread-safe by default; often used for Strings and wrapper classes.

• Rules to Create Immutable Class:

  1. Declare class final

  2. Make fields private and final

  3. No setters, only getters

  4. Initialize fields via constructor

• Example:

final class Person {
    private final String name;
    private final int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() { return name; }
    public int getAge() { return age; }
}

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5. Object via Cloning

• Definition: Object created as a copy of another object using clone() method.

• Characteristics: Shallow copy by default; deep copy requires custom implementation.

• Example:

class Car implements Cloneable {
    String brand;
    Car(String brand) { this.brand = brand; }
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
}
public class Main {
    public static void main(String[] args) throws Exception {
        Car c1 = new Car("BMW");
        Car c2 = (Car)c1.clone();
        System.out.println(c1.brand + " " + c2.brand);
    }
}

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6. Object via Deserialization

• Definition: Object recreated from a byte stream (saved file or network).

• Characteristics: Used to persist objects or send over network.

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✅ Summary Table