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Sep 10, 2024 · What are Java Exceptions? In Java, Exception is an unwanted or unexpected event, which occurs during the execution of a program, i.e. at run time, that disrupts the normal flow of the program’s instructions. Exceptions can be caught and handled by the program.
- Types of Exception in Java With Examples
To raise an exception of a user-defined type, we need to...
- Checked vs Unchecked Exceptions in Java
Below is the list of important built-in exceptions in Java....
- Types of Exception in Java With Examples
The try statement allows you to define a block of code to be tested for errors while it is being executed. The catch statement allows you to define a block of code to be executed, if an error occurs in the try block. The try and catch keywords come in pairs:
- Overview
- First Principles
- Exception Hierarchy
- Handling Exceptions
- Throwing Exceptions
- Anti-Patterns
- Conclusion
In this tutorial, we’ll go through the basics of exception handling in Java as well as some of its gotchas.
2.1. What Is It?
To better understand exceptions and exception handling, let’s make a real-life comparison. Imagine that we order a product online, but while en-route, there’s a failure in delivery. A good company can handle this problem and gracefully re-route our package so that it still arrives on time. Likewise, in Java, the code can experience errors while executing our instructions. Good exception handling can handle errors and gracefully re-route the program to give the user still a positive experience.
2.2. Why Use It?
We usually write code in an idealized environment: the filesystem always contains our files, the network is healthy, and the JVM always has enough memory. Sometimes we call this the “happy path”. In production, though, filesystems can corrupt, networks break down, and JVMs run out of memory. The wellbeing of our code depends on how it deals with “unhappy paths”. We must handle these conditions because they affect the flow of the application negatively and form exceptions: This code chooses no...
Ultimately, exceptions are just Java objects with all of them extending from Throwable: There are three main categories of exceptional conditions: 1. Checked exceptions 2. Unchecked exceptions / Runtime exceptions 3. Errors Runtime and unchecked exceptions refer to the same thing. We can often use them interchangeably.
In the Java API, there are plenty of places where things can go wrong, and some of these places are marked with exceptions, either in the signature or the Javadoc: As stated a little bit earlier, when we call these “risky” methods, we must handle the checked exceptions, and we mayhandle the unchecked ones. Java gives us several ways to do this:
If we don’t want to handle the exception ourselves or we want to generate our exceptions for others to handle, then we need to get familiar with the throwkeyword. Let’s say that we have the following checked exception we’ve created ourselves: and we have a method that could potentially take a long time to complete:
6.1. Swallowing Exceptions
Now, there’s one other way that we could have satisfied the compiler: The above is called swallowing an exception. Most of the time, it would be a little mean for us to do this because it doesn’t address the issue andit keeps other code from being able to address the issue, too. There are times when there’s a checked exception that we are confident will just never happen. In those cases, we should still at least add a comment stating that we intentionally ate the exception: Another way we can...
6.2. Using return in a finally Block
Another way to swallow exceptions is to return from the finallyblock. This is bad because, by returning abruptly, the JVM will drop the exception, even if it was thrown from by our code: According to the Java Language Specification:
6.3. Using throw in a finally Block
Similar to using return in a finally block, the exception thrown in a finallyblock will take precedence over the exception that arises in the catch block. This will “erase” the original exception from the tryblock, and we lose all of that valuable information:
In this article, we’ve gone through the basics of exception handling as well as some good and poor practice examples. As always, all code found in this article can be found over on GitHub!
We can use the try...catch block, finally block, throw, and throws keyword to handle exceptions in Java. In this tutorial, we will learn about Java exception handling with the help of examples.
Sep 11, 2023 · To raise an exception of a user-defined type, we need to create an object to his exception class and throw it using the throw clause, as: MyException me = new MyException(“Exception details”); throw me;
When an exception occurs within a method, it creates an object. This object is called the exception object. It contains information about the exception such as the name and description of the exception and state of the program when the exception occurred.
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Catching and Handling Exceptions. This section describes how to use the three exception handler components — the try, catch, and finally blocks — to write an exception handler. Then, the try-with-resources statement, introduced in Java SE 7, is explained.
