Java Variables

Java Print variable

Display Variables

The println() method is often used to display variables.

To combine both text and a variable, use the + character:

Example:

    String name = "John";
    System.out.println("Hello " + name);
      

You can also use the + character to add a variable to another variable:

Example:

   String firstName = "John ";
   String lastName = "Doe";
   String fullName = firstName + lastName;
   System.out.println(fullName);
      

For numeric values, the + character works as a mathematical operator (notice that we use int (integer) variables here):

Example:

    int x = 5;
    int y = 6;
    System.out.println(x + y); // Print the value of x + y
      

From the example above, you can expect:

• x stores the value 5

• y stores the value 6

• Then we use the println() method to display the value of x + y, which is 11

Java Declare Multiple Variables

Declare Many Variables

To declare more than one variable of the same type, you can use a comma-separated list:

Example:

Instead of writing:

    int x = 5;
    int y = 6;
    int z = 50;
    System.out.println(x + y + z);
      

You can simply write:

    int x = 5, y = 6, z = 50;
    System.out.println(x + y + z);
      

One Value to Multiple Variables

You can also assign the same value to multiple variables in one line:

Example

    int x, y, z;
    x = y = z = 50;
    System.out.println(x + y + z);
      

Identifiers Variables

All Java variables must be identified with unique names.

These unique names are called identifiers.

Identifiers can be short names (like x and y) or more descriptive names (age, sum, totalVolume).

Note: It is recommended to use descriptive names in order to create understandable and maintainable code:

Example

        // Good
    int minutesPerHour = 60;

    // OK, but not so easy to understand what m actually is
    int m = 60;
      

The general rules for naming variables are:

• Names can contain letters, digits, underscores, and dollar signs
• Names must begin with a letter
• Names should start with a lowercase letter, and cannot contain whitespace
• Names can also begin with $ and _ (but we will not use it in this tutorial)
• Names are case-sensitive ("myVar" and "myvar" are different variables)
• Reserved words (like Java keywords, such as or int or boolean) cannot be used as names