Why is the Java Object Class Not Abstract?

Why does Java's Object class not use the abstract keyword?

The Java Object class serves as the root of the class hierarchy in the Java programming language. Unlike other languages where the root class might be abstract, the Java Object class is concrete, allowing it to instantiate objects. This design choice has significant implications for object-oriented programming (OOP) in Java.

// Example of creating an Object instance and using it for synchronization.
Object lock = new Object();
synchronized(lock) {
   // critical section of code
}

Causes

• The Object class provides essential methods such as `equals()`, `hashCode()`, `toString()`, and `clone()` that are fundamental to many Java programs; thus, it needs to be instantiated.
• Having a concrete Object class allows developers to utilize Object instances for synchronization and as locks in multithreading scenarios.
• Java's design is intended to support polymorphism and message passing, where instances of classes can be treated as Objects, facilitating code flexibility.

Solutions

• To utilize the Object class, simply create an instance using the `new` keyword: `Object obj = new Object();` This allows you to employ it practically in lock mechanisms and synchronization, as mentioned.
• Understanding the implications of the non-abstract Object class can help in grasping concepts of inheritance and overriding methods for better code design.

Mistake: Assuming you can only use the Object class for locking via synchronized blocks.

Solution: While the Object class can be used for this, consider using dedicated locking objects or alternatives like ReentrantLock for better clarity and avoidance of potential deadlocks.

Mistake: Underestimating the utility of the Object class methods in everyday programming.

Solution: Always leverage methods like `equals()` and `hashCode()` when dealing with collections and custom classes to ensure proper function.