How To Fix Common Java Errors and Exceptions?

Introduction

Java programs can be a rewarding experience, but even the most skilled developers can run into errors that cause headaches and frustration if you've ever spent hours debugging to find the cause of errors.

In this article, you will learn the most common Java errors and tips to rectify them to help you streamline your programming workflow. You will find example code snippets and best practices.

Common Java errors

Some of the common errors encountered by Java developers are:

1. NullPointerException
2. ArrayIndexOutOfBoundsException
3. ClassCastException
4. ConcurrentModificationException
5. OutOfMemoryError
6. StackOverflowError

Here's the explanation for each of them.

NullPointerException

This error occurs when a program tries to access an object or variable that has not been initialized or is null (i.e., has no value assigned).

Let us see a couple of examples:

Examples

Example 1:
Following is a simple example with String variable that contains null.

// Example code that can result in a NullPointerException 
public class Error {  
	public static void main(String[] args) {  
		String str = null;  
		int length = str.length();  
		System.out.println(length);  // throws NullPointerException
	}  
}

We run into NullPointerException.

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.length()" because "str" is null
	at src.articles.Error.main(Error.java:6)

Why a NullPointer? String API has a lot of methods, and one of them is .length() that checks the length of the string that has been assigned.

We cannot call a .length() on null, it throws NullPointerException.

Example 2:

// Example code that can result in a NullPointerException 
public class Error {  
	public static void main(String[] args) {  
		Object obj = null;  
		System.out.println(obj.toString());  
	}  
}

We run into NullPointerException.

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.toString()" because "obj" is null
	at src.articles.Error.main(Error.java:6)

Same explanation, we cannot call the method .toString() on a null object.

Rectifying the error

public class Error {
    public static void main(String[] args) {
        // Rectified code
        String str = "Hello World";
        if (str != null) {
            int length = str.length();
        }
    }
}

ArrayIndexOutOfBoundsException

This error occurs when a program tries to access an element in an array with an index outside the array's bounds.

Illustration

Consider an array A[] that has 5 elements. To access the last element of the array, we use A[4].

With this knowledge, if N is the array length, then (N-1) is how we access the last element.

This small illustration helps you understand how we access array elements using their indexes.

What happens if we do A[-100], A[N], and A[N+1] ?

We run into ArrayIndexOutOfBoundsException.

Example

I hope you understand the above example. Here is the sample code depicting the above explanation.

// Example code that can result in an array index out of bounds exception 
public class Error {  
	public static void main(String[] args) {  
		int[] array = {1, 2, 3};  
		int value = array[3];  
	  
		System.out.println(value);  
	}  
}

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 3 out of bounds for length 3
	at src.articles.Error.main(Error.java:6)

Rectifying the error

public class Error {
    public static void main(String[] args) {
        // Rectified code
        int[] arr = {1, 2, 3};
        if (arr.length > 3) {
            int num = arr[3];
        }
    }
}

ClassCastException

This error occurs when a program tries to cast an object to a type that is not compatible with the actual type of the object.

Example

For example, trying to cast an Integer object to a String object will result in this error.

// Example code that can result in a ClassCastException
public class Error {
    public static void main(String[] args) {
        Object obj = "Hello World";
        Integer num = (Integer) obj;
    }
}

We run into ClassCastException.

Exception in thread "main" java.lang.ClassCastException: class java.lang.String cannot be cast to class java.lang.Integer (java.lang.String and java.lang.Integer are in module java.base of loader 'bootstrap')
	at src.articles.Error.main(Error.java:6)

Rectifying the error

public class Error {
    public static void main(String[] args) {
        // Rectified code
        Object obj = 5;
        if (obj instanceof Integer) {
            Integer num = (Integer) obj;
        }
    }
}

ConcurrentModificationException

This error occurs when a program tries to modify a collection while it is being iterated over, which can cause inconsistent behavior.

Example

For example, this error may occur if a program tries to remove an element from a collection while iterating over it.

import java.util.ArrayList;
import java.util.List;

public class Error {
    public static void main(String[] args) {
        List<String> list = new ArrayList<>();
        list.add("one");
        list.add("two");
        
        for (String str : list) {
            if (str.equals("one")) {
                list.remove(str);
            }
        }
    }
}

Rectifying the error

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Error {
    public static void main(String[] args) {
        // Rectified code
        List<String> list = new ArrayList<>();
        list.add("one");
        list.add("two");
        Iterator<String> iterator = list.iterator();
        while (iterator.hasNext()) {
            String str = iterator.next();
            if (str.equals("one")) {
                iterator.remove();
            }
        }
    }
}

OutOfMemoryError

This error occurs when a program runs out of memory, which can happen if it creates too many objects or doesn't release memory properly.

Example

import java.util.ArrayList;
import java.util.List;

public class Error {
    public static void main(String[] args) {
        // Example code that can result in an OutOfMemoryError
        List<Integer> list = new ArrayList<>();
        while (true) {
            list.add(Integer.MAX_VALUE);
        }
    }
}

We run into OutOfMemoryError.

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space

Rectifying the error

import java.util.ArrayList;
import java.util.List;

public class Error {
    public static void main(String[] args) {
        // Rectified code
        List<Integer> list = new ArrayList<>();
        try {
            while (true) {
                list.add(Integer.MAX_VALUE);
            }
        } catch (OutOfMemoryError e) {
            // Handle the error
            e.printStackTrace();
        }
    }

}

StackOverflowError

This error occurs when a program's call stack overflows, which can happen if a recursive function calls itself too many times or if there is an infinite loop.

Example

package src.articles;

public class Error {
    public static void main(String[] args) {
        recursiveCall(0);
    }

    // Example code that can result in a StackOverflowError
    public static void recursiveCall(int i) {
        recursiveCall(i++);
    }
}

We run into StackOverflowError.

Exception in thread "main" java.lang.StackOverflowError
	at src.articles.Error.recursiveCall(Error.java:13)
	at src.articles.Error.recursiveCall(Error.java:13)
	at src.articles.Error.recursiveCall(Error.java:13)

All the recursive method calls loaded into the stack are waiting to be executed. A base condition should be declared to avoid these errors.

Rectifying the error

public class Error {
    public static void main(String[] args) {
        recursiveCall(0);
    }

    // Rectified code
    public static void recursiveCall(int i) {
        if (i < 100) {
            recursiveCall(i + 10);
        }
    }
}

How can these errors impact the performance?

Errors in Java programming can impact the performance of a program in several ways:

1. Resource usage: Errors such as OutOfMemoryError can cause a program to use up more memory than necessary, resulting in slower performance and potential crashes.
2. Processing time: Errors such as StackOverflowError can cause a program to become stuck in an infinite loop, resulting in longer processing times and slower performance.
3. Inconsistent behavior: Errors such as ConcurrentModificationException can cause a program to behave unexpectedly, resulting in uneven or incorrect results.
4. Debugging time: Errors can also impact the time it takes to debug and fix a program, especially if the error is difficult to identify or caused by a complex interaction between different parts of the code.

Errors can significantly impact a program's performance, making it slower, less reliable, and more challenging to maintain. Developers can create more efficient, effective, and reliable programs by identifying and rectifying errors.

Best Practices for Rectifying Java Errors

Importance of testing and debugging

Testing and debugging are crucial parts of the software development process and play an essential role in identifying and rectifying errors in Java programming.

Here are some reasons why testing and debugging are essential:

1. Identifying errors early: Testing and debugging can help identify errors early in the development process, allowing developers to fix them before they become more complex and challenging to resolve.
2. Ensuring program functionality: Testing and debugging can help ensure that a program functions as intended, minimizing the risk of errors that could impact the user experience or result in crashes.
3. Saving time and resources: Identifying and rectifying errors early in the development process can save time and resources by preventing the need for more extensive debugging and rework later on.
4. Enhancing program quality: Testing and debugging can help improve a program's quality by identifying and resolving errors that could impact its performance or functionality.
5. Improving developer skills: Debugging can be a challenging but rewarding experience for Java developers, providing opportunities to enhance their skills and gain a deeper understanding of Java programming concepts.

Overall, testing and debugging are critical parts of the software development process that can help identify and rectify errors in Java programming, leading to higher-quality programs that meet the needs of end users.

Tips for handling exceptions, including try-catch and throw

Here are some tips for handling exceptions in Java programming:

Use try-catch blocks

They catch exceptions and handle them gracefully. By wrapping a block of code in a try block and specifying one or more catch blocks to handle specific exceptions, you can ensure that your program continues to run even if an exception occurs.

Specify exception types

When using try-catch blocks, it's important to specify the types of exceptions that each catch block can catch. This ensures that the correct catch block is executed for each exception type and can help you handle errors more effectively.

Use finally blocks

finally blocks are used to execute code that should always be run, regardless of whether an exception is thrown. This can be useful for cleaning up resources or ensuring certain actions are always taken.

Use throw statements

Throw statements can manually throw an exception, allowing you to handle errors more specifically and customized way. By specifying the type of exception to be thrown and any relevant error messages or details, you can create more informative and helpful error messages for users.

Handle exceptions at appropriate levels.

When handling exceptions, it's important to handle them at the appropriate level of your program. For example, you may want to catch exceptions at the method or application levels, depending on the nature of the error and its impact on the program.

Overall, handling exceptions in Java programming requires careful attention and thoughtful design. By using try-catch blocks, specifying exception types, using finally blocks, and throwing exceptions when appropriate, you can create more reliable, robust, and effective programs that meet users' needs.

Identifying the root cause of errors

Understanding the code and identifying the root cause of errors is crucial for effective error handling in Java programming. Here are some reasons why:

Efficient resolution: Understanding the code and identifying the root cause can help developers resolve errors more efficiently. By pinpointing the source of the error, developers can focus their efforts on fixing the specific issue rather than trying to solve a more general problem.

Preventing future errors: Identifying the root cause of an error can also help prevent similar errors from occurring in the future. By understanding how the error occurred and what factors contributed to it, developers can take steps to avoid similar mistakes in the future.

Improved code quality: By understanding the code and identifying the root cause of errors, developers can also improve the overall quality of their code. By identifying and fixing errors, developers can create more reliable, efficient, and effective programs that meet end-users needs.

More effective communication: Understanding the code and identifying the root cause of errors can also improve communication between developers. By sharing information about the error and how it was resolved, developers can work together more effectively, share knowledge, and improve their understanding of the codebase.

Understanding the code and identifying the root cause of errors is essential for effective error handling in Java programming. By taking the time to understand the code and identify the source of errors, developers can create more reliable, efficient, and effective programs that meet end-users needs.

Use of profiling and other debugging tools to identify and fix errors

Profiling and other debugging tools are powerful tools that can help identify and fix errors in Java programming. Here are some ways these tools can be used:

Identifying performance bottlenecks: Profiling tools can be used to identify performance bottlenecks in a program. By analyzing the program's memory usage, CPU utilization, and other metrics, developers can pinpoint areas of the program that are causing performance issues and take steps to optimize them.

Identifying memory leaks: Profiling tools can also identify memory leaks in a program. By tracking memory usage over time, developers can identify areas of the program that are not releasing memory properly and take steps to fix them.

Debugging complex errors: Other debugging tools, such as debuggers and code analyzers, can debug complex errors that are difficult to identify using other methods. By stepping through the code and analyzing its behavior, developers can identify the source of the error and take steps to fix it.

Improving code quality: Profiling and other debugging tools can also be used to improve the overall quality of a program. By identifying and fixing errors, optimizing performance, and eliminating memory leaks, developers can create more reliable, efficient, and effective programs that meet end-users needs.

Profiling and other debugging tools are essential for effective error handling in Java programming. By using these tools to identify and fix errors, developers can create more reliable, efficient, and effective programs that meet end-users needs.

Conclusion

In conclusion, Java errors are common for developers, but with proper understanding and handling, they can be rectified efficiently. The impact of errors can vary from program crashes to reduced performance, so it is crucial to test and debug code to identify and rectify errors. Tips such as using try-catch blocks and throw statements, understanding the code, and profiling and other debugging tools can be valuable in identifying and fixing errors.

We explored examples of common Java errors and exceptions, such as ArrayIndexOutOfBoundsException, ClassCastException, ConcurrentModificationException, OutOfMemoryError, StackOverflowError, and NullPointerException and how to rectify them. By using appropriate techniques and modifying the code, we can avoid errors and ensure that our Java programs run smoothly. It is essential to handle errors effectively to deliver reliable and robust software that meets our user's expectations.

What error do you think you primarily run into when working on a software product?