5 Common Errors You May See in Java Stack Traces and How to Avoid Them

5 Common Errors You May See in Java Stack Traces

Many different types of errors can occur in a Java application. The specific errors you see in a stack trace depend on the problem’s nature and the application’s characteristics. Some common errors that you might see in a stack trace include the following:

1. NullPointerException: This error occurs when your application tries to access or modify a null object reference. This can happen if you try to call a method on a null object, or if you try to access a field of a null object.
2. ArrayIndexOutOfBoundsException: This error occurs when your application tries to access an array element at an index that is outside the bounds of the array. This can happen if you try to access an array element with a negative index or an index larger than the array’s size.
3. ClassNotFoundException: This error occurs when your application tries to load a class that cannot be found. This can happen if the class is not on the classpath, or if the class has been removed or renamed.
4. NoSuchMethodError: This error occurs when your application tries to call a method that does not exist. This can happen if you have compiled your code against a version of a library other than the one you are using at runtime, or if you have made a typo in the method name.
5. OutOfMemoryError: This error occurs when your application tries to allocate more memory than is available in the Java heap. This can happen if you have a memory leak in your application or if you are trying to process very large data sets.

Here are some checks you can put in place to avoid these common errors

How to avoid NullPointerException

NullPointerException is a runtime exception that occurs when your Java application tries to access or modify a null object reference. Here are some ways you can avoid this exception:

Check for null values: Before accessing or modifying an object, make sure that it is not null. You can use an if statement to check for null values. For example:

if (obj != null) {
  // access or modify the object
} else {
  // handle the error
}

Use the optional class: You can use the Optional class to wrap an object and check for null values in a more concise way. For example:

Optional<String> opt = Optional.ofNullable(str);
if (opt.isPresent()) {
  // access the object
} else {
  // handle the error
}

Use the @Nonnull annotation: You can use the @Nonnull annotation to specify that a method or constructor parameter cannot be null. This can help prevent null pointer exceptions by making it easier to catch null values at compile time.

Initialize variables and fields: Make sure that variables and fields are initialized to a non-null value before you try to access them. If a variable or field is not initialized, it will have a default value of null, which can cause a null pointer exception when you try to access it.

How to avoid ArrayIndexOutOfBoundsException

ArrayIndexOutOfBoundsException is a runtime exception that occurs when your application tries to access an array element at an index that is outside the bounds of the array. Here are some ways you can avoid this exception:

Check the array bounds before accessing an element: Before accessing an element of an array, you should always check that the index is within the bounds of the array. You can do this by using an if statement to check if the index is less than the length of the array. For example:

if (index >= 0 && index < array.length) {
  // access the element
} else {
  // handle the error
}

Use a for loop to iterate over the array: If you are iterating over the elements of an array, you can use a for loop to avoid going out of bounds. The for loop will automatically stop when it reaches the end of the array.

for (int i = 0; i < array.length; i++) {
  // access the element at index i
}

Use the ArrayList class: If you need a resizable array, you can use the ArrayList class instead of an array. The ArrayList class automatically increases its size as needed, so you don’t have to worry about going out of bounds.

List<String> list = new ArrayList<>();
list.add("item 1");
list.add("item 2");
// access an element with list.get(index)

How to avoid ClassNotFoundException

ClassNotFoundException is a runtime exception that occurs when your Java application tries to load a class that cannot be found. Here are some ways you can avoid this exception:

Check the classpath: Make sure that the class you are trying to load is on the classpath.  The classpath lists directories and jar files that the JVM searches for classes. If the class is not on the classpath, the JVM will be unable to find it and throw a ClassNotFoundException.

Use the fully qualified class name: Make sure you use the fully qualified class name, including the package name, when loading the class. If you use the wrong class name, the JVM will not be able to find the class and will throw a ClassNotFoundException.

Check for spelling errors: Make sure there are no spelling errors in the class or package names. If there are spelling errors, the JVM will be unable to find the class and throw a ClassNotFoundException.

Check for missing dependencies: If the class you are trying to load depends on other classes or libraries, ensure that these dependencies are on the classpath. If a dependency is missing, the JVM will be unable to find the class and throw a ClassNotFoundException.

How to avoid NoSuchMethodError

NoSuchMethodError is a runtime error that occurs when your Java application tries to call a method that does not exist. Here are some ways you can avoid this error:

Check the method signature: Make sure that the method you are trying to call has the correct name and parameter types. If the method signature is incorrect, the JVM will not be able to find the method and will throw a NoSuchMethodError.

Check the class hierarchy: Make sure that the class you are calling the method on is correct. If you are calling a method on a subclass, make sure that the method is defined in the subclass or in one of its superclasses. If the method is not defined in the class hierarchy, the JVM will throw a NoSuchMethodError.

Check for spelling errors: Make sure that there are no spelling errors in the method name or parameter types. If there are spelling errors, the JVM will not be able to find the method and will throw a NoSuchMethodError.

Check for missing dependencies: If the class you call the method on depends on other classes or libraries, ensure that these dependencies are on the classpath.  If a dependency is missing, the JVM will be unable to find the method and throw a NoSuchMethodError.

How to avoid an OutOfMemoryError

OutOfMemoryError is a runtime error that occurs when your Java application tries to allocate more memory than is available in the Java heap.  Here are some ways you can avoid this error:

Monitor your application’s memory usage: FusionReactor can monitor your application’s memory usage and identify potential memory leaks. By monitoring your application’s memory usage, you can identify areas of your code that are using large amounts of memory and optimize them to reduce the risk of running out of memory.

Use a larger heap size: If your application requires a large amount of memory, you can increase the size of the Java heap by using the -Xmx command-line option when starting the JVM. For example, to set the maximum heap size to 2GB, you can use the following command:

java -Xmx2g MyClass

Use a memory-efficient data structure: If you are working with large data sets, you can choose a data structure that uses memory efficiently. For example, instead of using a HashMap to store large amounts of data, you could use a TreeMap, which uses less memory because it stores the data in sorted order.

Use a memory-efficient algorithm: You can also optimize your application’s memory usage by choosing algorithms that use memory efficiently.  For example, you can use an iterative algorithm instead of a recursive one, reducing the risk of running out of memory.

How do you find common errors in your Java application?

There are several ways to find common exceptions in a Java application:

• Reviewing log files: Exceptions are typically logged in the application’s log files. One way to find common exceptions is to review the logs and look for recurring exception messages regularly.
• Using an Application Performance Management (APM) tool such as FusionReactor: APM tools can monitor the performance of an application in real-time and provide detailed information about exceptions, including the frequency and cause of each exception.
• Setting up exception tracking and alerts: You can set up exception tracking and alerts in your application so that you are notified when specific exceptions occur and then analyze the data to identify common exceptions.
• Profiling your application: Profiling tools can give insight into how your application runs and help you identify performance bottlenecks and common exceptions.
• Using an exception handling framework: Some exception handling frameworks provide a way to group and count the exception by their type, message, or even custom tags.

It’s important to note that finding common exceptions is an ongoing process and requires regular monitoring and analysis of the application’s performance to ensure that the exceptions are identified and resolved promptly.

Conclusion – 5 Common Errors You May See in Java Stack Traces and How to Avoid Them

In this article; 5 Common Errors You May See in Java Stack Traces and How to Avoid Them, we have looked at these common errors that you might see in a stack trace: NullPointerException, ArrayIndexOutOfBoundsException, ClassNotFoundException, NoSuchMethodError, and the OutOfMemoryError. We have explained the errors and described how they could be avoided. If you are looking for less common exceptions, check out our post Diagnosing Less Common Java Exceptions: Techniques and Tools.