Difference Between Errors and Exceptions in Java
In Java, one of the main difference between errors and exceptions is that errors represent severe issues that indicate resource exhaustion or system problems beyond the program's control. Recovering from an error is generally impossible. On the other hand, exceptions represent unexpected events that occur during program execution due to issues within the code itself. These can often be handled using try-catch blocks to provide alternative behaviour or informative messages.
In Java, both errors and exceptions are subclasses of the Java Throwable class that belongs to java.lang package. Even though both are the subclass of the same class, they represent distinct issues that can arise during program execution.
Table of Content (TOC)
- Difference Between Errors and Exceptions
- What are Errors?
- Error Example
- What are Exceptions?
- Exception Example
- Key Differences Between Errors and Exceptions
Difference Between Errors and Exceptions
For better clarity, let's comprehend the difference between these two subclasses in a tabular format.
| Aspect | Error | Exception |
|---|---|---|
| Definition | A serious problem that cannot be recovered from, typically arising from system-level issues. | An issue that can disrupt the normal flow of a program but can be caught and handled. |
| Origin | System abnormalities such as hardware failures, system crashes, or out of memory. | Application code, including invalid input or incorrect API usage. |
| Recovery | Fatal and non-recoverable. | Can often be recovered from using try-catch blocks. |
| Types | Syntax Error, Runtime Error, Logical Error. | Checked Exceptions (detected at compile time) and Unchecked Exceptions (occur at runtime). |
| Examples | OutOfMemoryError, StackOverflowError. | IOException, NullPointerException, SQLException, etc. |
| Handling | Cannot be handled or caught by the program. | Can be caught and handled in the program to maintain flow or recover from the situation. |
| Hierarchy in Java | Extends the Error class in in Java’s class hierarchy. | Extends the Exception class in the hierarchy. |
| When They Occur | Can occur both at compile time and runtime. | Primarily occur at runtime, though checked exceptions can be detected at compile time. |
| Impact | May cause the program (and potentially the system) to terminate. | Disrupts the normal flow but allows for redirection or handling within the program. |
| Predictability | Unpredictable and often outside the control of the application. | Can be anticipated and handled through proper coding practices. |
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What are Errors?
Errors in Java denote serious issues that majorly occur at runtime due to external factors beyond the program's control. Common causes of these errors include critical system failures and resource limitations, such as running out of memory or encountering a stack overflow.
Due to their gravity, errors are represented by the Error class and its subclasses. Attempting to recover from them within the program is nearly impossible. Instead, the recommended approach is to log the error and exit the application. Some common examples of Java errors are:
- OutOfMemoryError: Occurs when the Java Virtual Machine (JVM) exhausts available memory resources.
- StackOverflowError: Arises when the call stack becomes too deep due to excessive method invocations.
- NoClassDefFoundError: Triggered when the JVM cannot locate a required class.
Error Example: OutOfMemoryError
public class ErrorExample { public static void main(String[] args) { try { // Intentionally create an array size that is too large to fit into memory int[] largeArray = new int[Integer.MAX_VALUE]; } catch (Throwable e) { // Catch the OutOfMemoryError System.out.println(e.toString()); } }}
Output:
Explanation: This example tries to allocate an array that's too large for the JVM's memory, causing an OutOfMemoryError. This error is caught by catching Throwable (the superclass of all errors and exceptions), and its type is printed. Usually, catching such errors is not recommended unless you're doing specific error handling or logging, as it indicates issues that an application usually cannot recover from by itself.
What are Exceptions?
Exceptions in Java are issues that occur within a program and disrupt the normal flow of its execution. These can be recoverable errors like NullPointerException and IllegalArgumentException. Java has two types of exceptions: checked and unchecked. They differ in their handling requirements.
- Checked Exceptions: These are known to the compiler at compile time, necessitating explicit handling within the code.
- Unchecked Exceptions: These are detected at runtime and are typically caused by programming errors, allowing for more flexibility in handling.
Developers can use try-catch blocks to manage exceptions effectively. This allows them to provide informative error messages to users and prevent program crashes.
Must Explore: Exception Handling in Java
Exception Example: FileNotFoundException
import java.io.File;import java.io.FileReader;
public class ExceptionExample { public static void main(String[] args) { try { // Attempt to open a file that does not exist File file = new File("nonexistent.txt"); FileReader fr = new FileReader(file); } catch (java.io.FileNotFoundException e) { // Catch the FileNotFoundException System.out.println(e.toString()); } }}
Output:
Explanation: This example attempts to open a file that does not exist, which throws a FileNotFoundException, a checked exception. The catch block catches this exception and prints its type and message. Unlike errors, exceptions like FileNotFoundException are expected to be handled by applications to either recover from the condition or provide informative feedback to the user.
Key Differences Between Errors and Exceptions
Here are the key differences between errors and exceptions:
- Errors indicate unrecoverable system issues beyond program control. In contrast, exceptions represent unexpected events within the program that can often be handled gracefully.
- All errors are subclasses of the java.lang.Error class. Meanwhile, all exceptions are subclasses of the java.lang.Exception class, which itself inherits from java.lang.Throwable.
- In Java, errors occur at runtime when the system encounters resource limitations. In contrast, exceptions occur both at runtime and compile time.
- Due to their unrecoverable nature, errors are not meant to be caught within the program. In contrast, exceptions can be caught and handled using try-catch blocks.
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FAQs
How do exceptions differ from errors?
Exceptions are used to handle recoverable issues within the program, whereas errors signify critical system failures that typically require program termination.
Can all errors and exceptions be prevented in Java programming?
While some errors and exceptions can be mitigated through careful coding and exception handling, others, such as critical system errors, may be unavoidable.
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