Difference Between final, finally, and finalize in Java

Have you ever wondered about the differences between final, finally, and finalize in Java? While final is used to create constants and prevent method overriding or class inheritance, finally is a block that executes after try-catch for guaranteed execution, typically for cleanup. On the other hand, finalize is a method called before an object's garbage collection, used for final resource release tasks. Let's understand more!

"final" is a keyword used to define immutable values or unchangeable behaviours in classes and methods. "finally" is a block in exception handling that ensures the execution of code regardless of whether an exception occurs."finalize" is a method that is called by the garbage collector before an object is destroyed, typically used for cleanup activities. Each plays a crucial role in the language's structure and behaviour management. In this blog, we will understand the differences between them!

Table of Content

• Difference Between Final, Finally, and Finalize in Java
• What is final in Java?
• What is finally in Java?
• What is finalize in Java?

Difference Between final, finally, and finalize

Below is a table differentiating between final, finally and finalize.

What is final in Java?

In Java, final is a keyword used to apply restrictions on classes, methods, and variables. When final is used with different Java entities, it has the following implications:

1. Final Variables

• A final variable cannot be reassigned once it has been assigned a value. This means once a final variable has been initialized, its value cannot be changed.
• It effectively makes the variable a constant. This is useful for defining values that should remain constant throughout the execution of a program, like final int MAX_SIZE = 100;
• A final variable must be initialized at the time of declaration or within the constructor if it is an instance variable.

2. Final Methods

• A final method cannot be overridden by subclasses. This is useful when you want to keep the implementation of a method unchanged in the inheritance hierarchy.
• It ensures that the semantic behaviour of the method stays consistent across different subclasses.

3. Final Classes

• A final class cannot be subclassed. This is a way to declare a class as "final" or "complete" and it cannot be extended further.
• It is useful when creating immutable classes like String or utility classes that should not be altered through inheritance.

What is finally in Java?

In Java, finally is a block used in conjunction with exception handling. It is part of the try-catch-finally construct and has the following characteristics:

1. Usage in Exception Handling

• The finally block is always executed after the try and catch blocks, regardless of whether an exception was thrown or caught.
• It is typically used for cleanup activities, such as closing file streams, releasing resources, or other necessary housekeeping tasks that should occur regardless of whether an error occurred or not.

2. Execution Characteristics

• The code inside a finally block will execute even if there's a return statement in the try or catch blocks.
• The only scenarios in which the finally block will not execute are if the JVM exits during the try or catch block, or if the thread executing the try or catch block is interrupted or killed.

3. Example

Here's a simple example to illustrate the use of finally

4. Importance

• The finally block is crucial for preventing resource leaks. For instance, if your try block opens a file for reading and an exception occurs, without a finally block to close the file, it would remain open.
• It ensures that important cleanup tasks are performed even if an unexpected exception disrupts the normal flow of code execution.

What is finalize in Java?

In Java, finalize is a method that is part of the Object class, the superclass of all classes in Java. The finalize method is called by the garbage collector on an object when there are no more references to that object, just before the garbage collector reclaims the memory used by the object. It's primarily intended for an object to release system resources or to perform other cleanup operations before it is garbage collected. Here are key points about finalize in Java:

1. Method Definition

The finalize method is declared in the Object class as protected void finalize() throws Throwable.

2. Usage and Purpose

• It's used to perform cleanup operations on objects that the garbage collector is about to collect.
• Typically, these cleanup operations might include closing file streams, releasing network connections, or freeing up any other system resources that the object holds.

3. Automatic Invocation

• You do not call the finalize method explicitly in your code. It is invoked automatically by the garbage collector.
• There is no guarantee when, or even if, the finalize method will be invoked. The timing depends on the garbage collector, which operates asynchronously.

4. Override in Subclasses

Subclasses override the finalize method to dispose of system resources or to perform other cleanup.

5. Caution in Use

• Relying on finalize is generally not recommended. It creates unpredictability since you can't be certain when, or even if, the garbage collector will invoke it.
• The use of finalize is often associated with poor performance and unpredictable behaviour. As of Java 9 and later, the finalize method is deprecated.

6. Alternatives

Java offers better alternatives for managing resources, such as try-with-resources and the AutoCloseable interface, which provide a more predictable way of releasing resources.

7. Example

Here is a basic example of overriding the finalize method

Thus, each of these plays a vital role in Java programming, but they serve very different purposes and should be understood and used accordingly to write efficient and clean Java code.

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