Java: Data Types
Data types in Java are divided into two important groups according to how variables of this type are related and the values stored in them.
What will the following code output?
var a = 10;
var b = a;
a = 20;
System.out.print(b);
10 will be output, because with the assignment b = a, the number 10, which at this moment is contained in a, will be written into the variable b.
If you write
var a = "string";
var b = a;
- then the situation will be different.
Briefly
Primitive data types in Java:
- Strings in quotes
- The numbers
7,-198,0and so on
In fact, there are more, but now let's talk only about them.
There are different ways to present data in programs.
There are strings - character sets in quotes like "Hello, World!". There are integers - for example, 7, -198, 0. These are two different categories of information - two different data types.
The multiplication operation makes sense for integers but it does not make sense for strings: to multiply the word "mother" by the word "notepad" is nonsense.
The data type determines what can be done with the elements of a specific set of information.
A programming language recognizes types. Therefore, Java will not allow us to multiply a line by line (“multiply text by text”). But it will allow to multiply an integer by another integer. The presence of types and such restrictions in the language protects programs from random errors.
Unlike strings, numbers do not need to be wrapped in quotes. To print the number 5, just write:
System.out.print(5);
Note that the number 5 and the string "5" are completely different things, although the output of println for this data is identical.
Integers (1, 34, -19, etc.) and rational numbers (1.3, 1.0, -14.324, etc.) are two separate types data. This separation is associated with the characteristics of the device computers. There are other types, we will get to know them later.
Here is another example, but with a rational number:
System.out.print(10.234);
The lines in programming are called "strings", and the lines of text files are called "lines". For example, the code above has one line (lines), and there are no lines (strings). In all the lessons we will say string to indicate the data type "string", and line to indicate lines (lines) in files).
Programmers themselves can create new data types, albeit with certain restrictions.
Instructions
Display the number -0.304.
The exercise doesn't pass checking. What to do? 😶
If you've reached a deadlock it's time to ask your question in the «Discussions». How ask a question correctly:
- Be sure to attach the test output, without it it's almost impossible to figure out what went wrong, even if you show your code. It's complicated for developers to execute code in their heads, but having a mistake before their eyes most probably will be helpful.
In my environment the code works, but not here 🤨
Tests are designed so that they test the solution in different ways and against different data. Often the solution works with one kind of input data but doesn't work with others. Check the «Tests» tab to figure this out, you can find hints at the error output.
My code is different from the teacher's one 🤔
It's fine. 🙆 One task in programming can be solved in many different ways. If your code passed all tests, it complies with the task conditions.
In some rare cases, the solution may be adjusted to the tests, but this can be seen immediately.
I've read the lessons but nothing is clear 🙄
It's hard to make educational materials that will suit everyone. We do our best but there is always something to improve. If you see a material that is not clear to you, describe the problem in “Discussions”. It will be great if you'll write unclear points in the question form. Usually, we need a few days for corrections.
By the way, you can participate in courses improvement. There is a link below to the lessons course code which you can edit right in your browser.