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LESSON 4 OF 410 · WELCOME TO JAVA

Variables in Java

Lesson

In computer science, data is anything that is meaningful to the computer. Java provides a large number of data types, the most frequently used being:

  • int - represents integer numbers like 3 and -12
  • double - represents floating point numbers like 3.14
  • char - represents a single character like 'a', 'Z' or '?'
  • String - represents a sequence of characters like "John Doe"
  • boolean - represents one of two values: true or false

For example, computers distinguish between numbers, such as the number 12, and strings, such as "12", "dog", or "123 cats", which are collections of characters. Computers can perform mathematical operations on a number, but not on a string.

Variables are containers for storing values. A piece of information / data lives in memory and we use a variable to store and descriptively label that data.

Variable declaration:

To create / declare a variable, we must tell Java the variable's data type followed by the variable's name, like so:

String name;

creates a String variable named name.

Variable initialization:

We can initialize a variable to an initial value in the same line as it is created using the assignment operator (=). This code:

String name = "AlgoCademy";

creates a new String variable named name and assigns it an initial value of "AlgoCademy".

When executing this code, Java will allocate some memory, then it will store the string "AlgoCademy" in that memory and finally will attach this name label to that memory location.

You can think of this memory location as a box. In that box, we put string "AlgoCademy". Then, we put the label name on this box.

Accessing values in variables:

Now we can use this label anywhere in our program to access the value in that box. We can print it for example:

// We create and initialize two variables:
String name = "AlgoCademy";
int age = 10;

// We access the variables:
System.out.println(name);
System.out.println(age);

The output of this code is:

AlgoCademy
10

Important notice:

We almost never want to create a variable without initializing it! It's a bad coding practice and can create a lot of problems.

Assignment
Follow the Coding Tutorial and let's create some variables.

Hint
Look at the examples above if you get stuck.

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