☕Understanding `final`, `finally`, and `finalize` in Java

☕Understanding `final`, `finally`, and `finalize` in Java | ZhenXiao Mark Yu

Java programming involves a myriad of keywords, each serving distinct purposes to enhance the functionality and robustness of the code. Among these, final, finally, and finalize often cause confusion due to their similar nomenclature. However, they serve entirely different purposes. This article will elucidate the differences between these keywords, their uses, and practical examples to clarify their roles in Java programming.

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Introduction

In Java, final, finally, and finalize are keywords with distinct functions:

final: A keyword used in variable, method, and class declarations to denote constants, prevent method overriding, and inheritance.
finally: A block used in exception handling to execute code regardless of whether an exception is thrown or not.
finalize: A method used to perform cleanup operations before an object is garbage collected.

Understanding the differences and applications of these keywords is crucial for writing effective Java code.

The `final` Keyword

Purpose

The final keyword is versatile and can be applied to variables, methods, and classes.

Use Cases

Final Variables: When applied to a variable, the final keyword makes it a constant, meaning its value cannot be changed once assigned.
Final Methods: When applied to a method, it prevents the method from being overridden by subclasses.
Final Classes: When applied to a class, it prevents the class from being subclassed.

Code Examples

Final Variables

public class Constants {
    public static final int MAX_USERS = 100;
    public static final String APP_NAME = "MyApp";
}

In this example, MAX_USERS and APP_NAME are constants that cannot be changed.

Final Methods

public class Parent {
    public final void display() {
        System.out.println("This is a final method.");
    }
}

public class Child extends Parent {
    // This will cause a compile-time error
    // public void display() {
    //    System.out.println("Attempting to override a final method.");
    // }
}

Here, the display method in the Parent class cannot be overridden by the Child class.

Final Classes

public final class Utility {
    public static void performTask() {
        System.out.println("Performing a task.");
    }
}

// This will cause a compile-time error
// public class AdvancedUtility extends Utility {
// }

The Utility class cannot be subclassed due to the final keyword.

The `finally` Block

Purpose

The finally block is used in exception handling to execute code that must run regardless of whether an exception is thrown or caught.

Use Cases

Resource Management: Ensuring resources like files and database connections are closed properly.
Cleanup Operations: Performing necessary cleanup actions after try-catch blocks.

Code Example

public class FileOperations {
    public void readFile(String filePath) {
        FileReader fileReader = null;
        try {
            fileReader = new FileReader(filePath);
            // Perform file operations
        } catch (IOException e) {
            System.out.println("An error occurred: " + e.getMessage());

In this example, the finally block ensures that the FileReader resource is closed regardless of whether an exception occurs.

The `finalize` Method

Purpose

The finalize method is invoked by the garbage collector before an object is reclaimed. It is used to perform cleanup operations, such as releasing resources.

Use Cases

Cleanup Operations: Performing cleanup before an object is garbage collected.

Code Example

public class ResourceHolder {
    private FileReader fileReader;

    public ResourceHolder(String filePath) throws FileNotFoundException {
        this.fileReader = new FileReader(filePath);
    }

    @Override
    protected void finalize() throws Throwable {
        try {
            if (fileReader != null

Here, the finalize method ensures that the FileReader is closed before the ResourceHolder object is garbage collected. However, it's important to note that the finalize method is deprecated in recent Java versions due to unpredictability and better alternatives like try-with-resources and explicit resource management.

Summary

In summary, final, finally, and finalize are three distinct keywords in Java with different purposes:

final: Used to declare constants, prevent method overriding, and inheritance.
finally: A block used in exception handling to execute necessary code regardless of exceptions.
finalize: A method used for cleanup operations before an object is garbage collected (now largely deprecated).

Understanding these keywords helps in writing more robust, maintainable, and efficient Java code. By using final, you can create immutable variables and secure methods and classes. The finally block ensures resource management and cleanup, while finalize (despite its deprecation) shows the historical approach to object cleanup before garbage collection.

References:

☕Understanding `final`, `finally`, and `finalize` in Java

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Understanding the `throw` and `throws` Keywords in Java

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Introduction

The `final` Keyword

Purpose

Use Cases

Code Examples

Final Variables

Final Methods

Final Classes

The `finally` Block

Purpose

Use Cases

Code Example

The `finalize` Method

Purpose

Use Cases

Code Example

Summary

相关阅读

Understanding the `throw` and `throws` Keywords in Java

Advanced Java: Simplifying Object Property Copy and Manipulation with BeanUtil

The True Cost of Poor Data Quality: Why It Matters and How to Improve It

Introduction

The final Keyword

Purpose

Use Cases

Code Examples

Final Variables

Final Methods

Final Classes

The finally Block

Purpose

Use Cases

Code Example

The finalize Method

Purpose

Use Cases

Code Example

Summary

The `final` Keyword

The `finally` Block

The `finalize` Method