Lessons

Marines believe that if you have physically able men and women, you can make extraordinary soldiers out of virtually all of them with the proper training. Programming is a skill just like playing the guitar, swimming, or riding a bike...

Learning based on practice There are people who love CodeGym with all their hearts, and there are people who hate it with all their hearts. But even CodeGym's most vicious critic will readily agree that it has an impressively huge number of tasks. And the reason why there are so many of them is because all CodeGym training...

Community. At CodeGym, we believe that exchanging knowledge between students is extremely valuable. As programmers help others, they themselves grow. And there's no better way to understand something yourself than to explain it to someone else. That's why we have created special sections on our website that...

Programs are divided into blocks. A block can be a class, or a method, or an operator. Java variables can be seen from one block but not another. This may seem superfluous to the beginner, but it's actually very convenient (and very important!). This lesson introduces you to variable scope and access modifiers.

It's time to dig deeper and understand what variables exist only at the level of a command, which exist until a method returns, and which exist as long as an object is alive. In this lesson, we'll try to understand the access modifiers "public" and "private". And let's also take a first look the special independent variables we call static.

There are no completely invisible variables. That would be pointless! But one may be visible throughout an entire object. Another may only be visible in a loop or another block. This approach may seem complicated, but it's actual completely logical. The same thing is true in life: homes aren't visible over a mountain, and from the street you can't see someone sitting at a computer and completing tasks about the visibility of variables.

On the fourth level, CodeGym students already know that in Java a code block is bounded on each side by curly brackets, and that each command ends with a semicolon... Or don't they know that yet? Or do they not know it, but instead intuitively feel it? In any case, it's time to deal with these concepts—the command and the code block.

Without conditional statements, a programmer must move straight ahead and never turn around. This is uninteresting and inefficient. So on the fourth level, it's time to teach branching. This will let us write smarter programs that can make choices. At least, like this: If (a == “right?”) {“sing song”} else if (a == “left?”) {“tell story”}.

We're not absolute. To realize our place in the world, we must compare ourselves with others... Uh, wait, why are we slipping into philosophy? In Java, mathematical comparisons are performed in the most ordinary way. In this lesson, we'll delve into comparison operators. We'll use them to create conditional statements and complete some interesting tasks to reinforce what you learn.

Evaluating integer expressions. The right side of an assignment operator (equal sign) can be any expression — any combination of numbers, variables, and mathematical operators (+, -, *, /). You can also use parentheses (). In Java, as in mathematics, expressions inside parentheses are evaluated first, and then what is outside the parentheses.

Remember the game "Truth or Lie"? Oh, wait. The game is called "Truth or Dare". "Truth or Lie" is the critical question for all logical tasks. This boils down to the fact that Java has a special type that can take only 2 values. You guessed correctly. These 2 values are true and false.

"Greetings, Amigo! I was so carried away by solving logic problems that I didn't notice you come in. Here's one for you: if crocodiles fly, then snow is white. There's a flying crocodile. What's the conclusion?" "Um... So we conclude that snow is white?" "Excellent. You passed the initiation test. You are ready to master the next topic...