Question

State true/false: (a) Abstract class cannot be instantiated. (b) A final method can be overridden. (c) Declaring a method synchronized guarantees that the deadlock cannot occur. (d) Volatile modifier is used to modify by synchronous threads.

Short answer

(a) True, (b) False, (c) False, (d) False.

Step-by-step solution

Understanding Abstract Classes

An abstract class is a class that cannot be instantiated on its own and may include incomplete methods that are meant to be implemented by subclasses. This characteristic means such classes are designed to be subclasses rather than used directly.

Final Method Properties

A final method in Java is a method that cannot be overridden by subclasses. This is a way to prevent any class from modifying the behavior defined by an inherited method.

Synchronized Method and Deadlocks

Synchronized methods ensure that only one thread can access the method at a time. However, using synchronized methods does not prevent deadlocks, which can occur if two or more threads are waiting forever for locks held by each other.

Volatile Modifier Explanation

The volatile modifier in Java indicates that a variable's value may be changed by different threads. It guarantees visibility but does not ensure atomicity or synchronization.

Key concepts

Abstract Class

An abstract class in Java represents a blueprint for other classes. It allows you to define methods that can be shared among multiple subclasses. However, you cannot create an instance of an abstract class directly. This is because abstract classes often include abstract methods—methods declared without an implementation.
These must be completed in the subclasses, allowing different classes to share a common template while still providing room for diversity in implementations.

• Purpose: Abstract classes are used to group related classes under a common banner, sharing code where possible.
• Instantiation: Instantiation of an abstract class is not possible directly, you can only instantiate concrete subclasses.
• Method Behavior: Abstract methods within these classes must be implemented by any concrete subclass, ensuring that these subclasses follow a certain structure.

Final Method

The final method is an essential concept in Java when you want to restrict methods from being overridden by subclasses. A method marked as final cannot be changed by any subclass. This is particularly useful when you want to ensure that the functionality implemented in the method remains constant across all instances of subclasses.
Why use a final method? This concept helps maintain the integrity of the method’s implementation, safeguarding it from unintended modifications.

• An effective way to prevent overriding, ensuring the method’s operation stays consistent.
• Useful in security-sensitive applications where the method’s behavior should remain unaltered.
• Although final restricts overriding, it does not affect method overloading, which is allowed.

Synchronized Method

A synchronized method in Java ensures that only one thread executes the method at a time. By using synchronized, you can prevent inconsistent data and ensure thread safety when multiple threads are accessing shared data.
However, synchronized methods aren't a panacea for all multithreading issues. They do not inherently eliminate deadlocks, which can happen when two or more threads end up stuck, waiting for each other's locks.

• Ensures thread safety by allowing only one thread to execute at a time.
• Prevents race conditions but requires careful design to avoid deadlocks.
• Exercise caution to ensure the synchronized code does not become a bottleneck.

Volatile Modifier

The volatile modifier in Java is used when you're dealing with variables that might be modified by multiple threads simultaneously. It ensures visibility, which means when one thread changes the value of a volatile variable, other threads get the updated value immediately. However, the volatile modifier does not guarantee atomicity—a property where an operation is completed as a single indivisible entity.
This feature prevents threads from reading stale data, however, it does not synchronize access between threads. This means while threads can see the latest updated values, complex operations need additional synchronization mechanisms to avoid race conditions.

• Ensures visibility of changes to variables across threads.
• Does not prevent thread interference or race conditions.
• Best used for simple flags and similar scenarios where atomicity is not a concern.