Anonymous Class in Java – Definition, Syntax, and Example

Singleton Class in Java – Definition, Syntax, and Example

Definition:

A Singleton Class in Java is a design pattern that ensures only one instance of the class exists in the JVM. It provides a global point of access to that instance.

Key Points:

• Only one instance is created during the entire lifecycle.
• Private constructor to prevent external instantiation.
• Static method to provide access to the single instance.

Syntax Example:

public class Singleton {
    private static Singleton instance;

    private Singleton() {
        // private constructor
    }

    public static Singleton getInstance() {
        if (instance == null) {
            instance = new Singleton();
        }
        return instance;
    }
}

public class Main {
    public static void main(String[] args) {
        Singleton obj1 = Singleton.getInstance();
        Singleton obj2 = Singleton.getInstance();
        System.out.println(obj1 == obj2); // true
    }
}

Advantages:

• Controlled access to the single instance.
• Reduces memory footprint.
• Ensures consistent state across application.

Limitations:

• Difficult to test with multiple instances.
• Can introduce global state issues.

❓ Frequently Asked Questions

Q1: Can a Singleton class have parameters in the constructor?

No. Singleton constructors are private and parameters are not allowed for external calls.

Q2: Is Singleton thread-safe by default?

No, you need to implement synchronization for multi-threaded environments.

Q3: Can Singleton be broken by serialization?

Yes, unless you override readResolve() method.

📚 Related Java Class Concepts

• Concrete Class in Java
• Anonymous Class in Java
• Inner Class in Java
• Singleton Class in Java
• Static Nested Class in Java
• POJO Class in Java
• Final Class in Java
• Abstract Class in Java