Key differences between Checked Exception in Java and Unchecked Exception in Java

Checked Exception in Java

In Java, a checked exception is a type of exception that is checked at compile-time rather than at runtime, meaning that the compiler requires the code to handle these exceptions either with a try-catch block or by declaring them with a throws clause in the method signature. These exceptions are part of the Exception class but do not include RuntimeException and its subclasses. Checked exceptions are used to handle recoverable conditions that occur outside the immediate control of the program, such as IOExceptions, SQLExceptions, or ClassNotFoundExceptions. They promote robust code by forcing developers to anticipate and mitigate conditions that might cause the program to terminate abnormally, thus improving the reliability and maintainability of applications.

Functions of Checked Exception in Java:

  • Enforcing Error Handling:

Checked exceptions require explicit handling; the compiler enforces that these exceptions are either caught or declared to be thrown. This ensures that error handling is not overlooked by the developer.

  • Improving Program Reliability:

By mandating handling of potential error conditions, checked exceptions encourage writing more robust and fault-tolerant code.

  • Documenting API:

When a method declares an exception, it becomes part of its signature, thus serving as a form of documentation. This informs users of the method about the potential issues they must consider when using it.

  • Promoting Thoughtful Error Management:

The necessity to handle or declare checked exceptions makes developers think critically about the possible causes of an error and how to manage it, leading to more deliberate and safer error management strategies.

  • Facilitating Graceful Recovery:

Handling checked exceptions allows the program to continue operation after a recoverable error, promoting a smoother user experience and preventing the program from crashing unexpectedly.

  • Encouraging Detailed Exception Handling:

Since checked exceptions can be subclassed to create more specific error types, they help in implementing detailed and specific error handling that can address various issues distinctly.

  • Separating Error Handling from Business Logic:

Checked exceptions help in separating the normal control flow from the error handling code, thus maintaining cleaner and more maintainable code.

  • Aiding in Debugging and Maintenance:

Since checked exceptions must be declared or handled, they can provide clues to developers during debugging and maintaining the code, as they pinpoint where things can go wrong.

Example of Checked Exception in Java:

In this example, the method readFile throws a checked exception FileNotFoundException which must be either caught or declared to be thrown


public class FileOpener {

    public void readFile(String filePath) throws FileNotFoundException {

        File file = new File(filePath);

        if (!file.exists()) {

            throw new FileNotFoundException(“File not found at path: ” + filePath);


        BufferedReader br = new BufferedReader(new FileReader(file));

        String line;

        try {

            while ((line = br.readLine()) != null) {



        } catch (IOException e) {

            System.out.println(“An error occurred while reading the file.”);

        } finally {

            try {


            } catch (IOException e) {

                System.out.println(“Failed to close the file.”);




    public static void main(String[] args) {

        FileOpener fo = new FileOpener();

        try {

            fo.readFile(“example.txt”); // specify the correct file path

        } catch (FileNotFoundException e) {





In this example:

  • The method readFile is declared to throw FileNotFoundException, a checked exception that must be either caught or declared by any method that uses readFile.
  • The main method uses a try-catch block to handle the FileNotFoundException thrown when attempting to open a file that does not exist.
  • This code exemplifies how Java enforces handling of checked exceptions to ensure robust error management.

Unchecked Exception in Java

Unchecked exceptions in Java are a category of exceptions that include runtime exceptions and errors. These exceptions are not checked at compile-time, meaning the compiler does not require methods to catch or declare them. This type of exception typically reflects programming errors, such as logic errors or improper use of an API. Unchecked exceptions include NullPointerException, ArithmeticException, ArrayIndexOutOfBoundsException, and similar issues that can arise during runtime. They are derived from the RuntimeException and Error classes, which are subclasses of the Exception class. The use of unchecked exceptions in Java simplifies coding by not forcing developers to handle or declare these exceptions, which are often indications of bugs that should be fixed in the code rather than merely handled.

Functions of Unchecked Exception in Java:

  • Simplifies Error Handling:

Unchecked exceptions are not required to be declared in a method’s throws clause, simplifying the coding process by reducing boilerplate code related to exception declarations.

  • Indicates Programmer Errors:

Unchecked exceptions often indicate bugs, such as logic errors or incorrect API usage (e.g., NullPointerException, IndexOutOfBoundsException). This helps in identifying and fixing programming errors that should not occur under normal circumstances.

  • Promotes Code Readability:

By not forcing the programmer to catch them or declare them in the method signature, unchecked exceptions reduce clutter in the code, enhancing readability and maintainability.

  • Encourages Good Programming Practices:

The use of unchecked exceptions encourages programmers to perform necessary null checks and validate arguments before method execution, adhering to good programming practices.

  • Facilitates Runtime Error Management:

Since unchecked exceptions represent conditions that a reasonable application should not try to catch, they help in managing errors that are typically due to programming mistakes and should ideally be fixed during development rather than handled at runtime.

  • Minimizes Exception Handling Overhead:

By eliminating the need for extensive exception checks at runtime for scenarios that are unlikely to occur, unchecked exceptions can potentially improve the performance of Java applications.

  • Improves API Design:

They provide a way for API designers to indicate to the developers about which exceptions are a result of programmatic errors versus those which are genuine exceptional conditions that the calling code should handle.

  • Enhances Propagation:

Unchecked exceptions propagate up the call stack until they are caught in a catch block or cause the program to terminate, allowing developers to handle them at an appropriate level rather than at every step where they might occur.

Example of Unchecked Exception in Java:

An example of an unchecked exception in Java is a NullPointerException. This occurs when your program attempts to use an object reference that has not been initialized. Here’s a simple example to illustrate how a NullPointerException can occur and how it can be handled (though typically it’s better to avoid such exceptions through null checks rather than handling them after they occur):

public class Main {

    public static void main(String[] args) {

        Person person = null;

        try {

            // Trying to access a method on a null reference


        } catch (NullPointerException e) {

            System.out.println(“Caught NullPointerException”);


        // Proper handling by checking if the object is null

        if (person != null) {


        } else {

            System.out.println(“Person object is not initialized”);



    static class Person {

        public void display() {

            System.out.println(“This is a Person object.”);




In this example:

  • The Person object person is declared but not initialized, hence it is null.
  • The attempt to invoke display() on a null object reference leads to a NullPointerException.
  • The exception is caught in the catch block, which prints a message indicating that a NullPointerException was caught.
  • A proper null check is demonstrated to prevent the exception from being thrown in the first place.

Key differences between Checked Exception in Java and Unchecked Exception in Java

Aspect Checked Exception Unchecked Exception
Compilation Check Checked by compiler Not checked by compiler
Handling Requirement Must be handled or declared No handling required
Keyword Usage Uses throws Usually no throws
Propagation Propagated with throws Propagated by JVM
Control Flow Affects control flow May disrupt control flow
Error Type Recoverable Often not recoverable
Examples IOException, SQLException NullPointerException, ArithmeticException
Package Mostly, java.sql Mostly java.lang
Catch Block Required for compilation Optional
Transaction Handling Often involves transaction roll-back Usually no transactions affected
Usage Scenario External system issues Programming errors
Programmer Control External factors Programmer’s logic errors
When to Use When caller can recover Runtime errors, bugs
Documentation Documented in JavaDoc Rarely documented
Impact on Program Design Influences API design Lesser impact on design

Key Similarities between Checked Exception in Java and Unchecked Exception in Java

  • Inheritance:

Both types of exceptions inherit from the java.lang.Exception class, although unchecked exceptions are further derived from java.lang.RuntimeException.

  • Throwable:

Both are a type of Throwable, which means they can be thrown and caught using try, catch, and finally blocks.

  • Object Type:

Each is an object in Java and behaves as any other object in terms of object-oriented features like methods and fields.

  • Purpose:

Both are used for handling errors in a program, providing a means to separate error-handling code from regular code logic.

  • Can be Thrown:

Both checked and unchecked exceptions can be explicitly thrown using the throw keyword within a method.

  • Can be Created:

Both types of exceptions can be defined by users by extending either Exception or RuntimeException classes.

  • Run-Time Behavior:

Regardless of being checked or unchecked, when an exception is thrown at runtime, it causes the normal flow of execution to be disrupted unless it is caught within a try-catch block.

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