Lessons

You can learn to program and not become a programmer, but instead apply your new skill to advance your current career Sergey, a Moscow resident, shared his success story with CodeGym students. He used the course to study for 3.5 years, but still isn't working as a developer. What went wrong? Or perhaps everything...

A stack obeys the "first in, last out" principle. In Java, the StackTrace rule says: Remember that the last function called is the first function to end. That is, if function A calls function B, which calls function C, which calls function D, then returning from function B requires that we first return from function C, which requires that we first return from function D.

A stack is like a stack of plates at a cafeteria. If for some reason the third plate from the top catches your fancy, you'll have to remove the top two to get to it. The Java call stack is a special collection that the virtual machine uses to record all function calls. We'll learn how to get the plate we want by completing some tasks involving StackTrace.

Previously, when an error occurred in a method, the program would terminate. Now the Java machine creates a special object (an exception), which stores information about the error. The program exits the current method, then exits the method that called that method, and so on until it reaches the main method. For the program to continue working, the exception must be "caught".

In Java, exceptions are divided into two types: checked and unchecked, i.e. exceptions that must be caught and exceptions that do not have to be caught. By default, all exceptions must be caught. Now we'll try to understand how to work with exceptions thrown by the Java machine.

Exceptions are a very elegant and convenient mechanism for dealing with errors. But to work with them, you must understand some things about Java programming, and you need to get used to how the call stack unwinds. In this lesson, let's look at an example of how to create, throw, and catch exceptions.

By Level 9, CodeGym students have already completed dozens of tasks. But not without some mistakes, right? Previously, the program would terminate if an error occurred. Now Java has exceptions and a special "trap" for exceptions: the try-catch block. Let's complete several tasks involving exceptions while working with numbers, strings, arrays, and collections.

The catch statement, which is used to catch exceptions, can catch multiple exceptions. What does using a single multi-catch block do for you? It makes code simpler and more understandable, eliminates repetition, and is mood-enhancing (this last property is an optional consequence of using multi-catch).

How multi-catch works? If an exception occurs in a try block, execution of the program jumps to the first catch. If the type specified inside the catch statement matches the exception type, then the code inside the {} block starts executing. Otherwise, execution moves to the next catch and the check is repeated. Now let's practice to help reinforce this concept.

In this level, you learned how and why exceptions occur. This is a very important topic for your future work as a programmer. We are sure you won't be hurt by seeing a few more real-world examples and a couple of additional articles. Catching and handling exceptions This interesting article will help...