Variable

Just as in other programming languages, in Java, variable is also the basic unit needed to store a value to a specific data type in the computer's memory. Every variable has a scope and the time to live in the memory.

Variable Declaration

Here is the general form to declare variables in Java:

type variableName;   //to declare a variable
type variableName1, variableName2;   //to declare several variables

For example, if we want to declare a variable with name x and data type int, then we should write it as follows:

int x;

You can also declare some variable with the same type at once by using commas as its separator, as shown in the code below:

int x, y, z;   //declare variable x, y, z with int type
char ch1, ch2   //declare variable ch1, ch2 with char type

There are some rules to be considered in determining the variable name at the time of the declaration process, which is as follows:

• Variable name can not contain spaces.
• Variable name must not be preceded by a number or numeric characters (digits).
• Variable name must not contain the symbol, except for the $ sign.
• Variable name must not contain the keywords that have been defined in Java salutation, eg: while, break.
• In a program block, the variable name must be unique or different from one another.
• Keep the variable names as descriptive as possible so that the program code can be more easily understood by others (especially when working with the team).

In Java, variable names always begin with a lowercase letter, for example: hairColor, isExist, and so forth. This also applies to the method name in a class, for example: toString(). We will discuss about the method on next post.

Variable Initialization

Java allows us to initialize the value in variable declaration. The initial value is the value used as the initial (default) before finally variable is filled/replaced with another value. The general form of variable Initialization is as follows:

type variableName = value;
type variableName1 = value1, variableName2 = value2;

Here are two examples of code that demonstrates the variable Initialization:

int index = 0;
char ch = 'A';

The above code shows that we declare a variable named index and type int with 0 as initial value, and a variable named ch and type char with 'A' as initial value.

Scope and Life Cycle of Variable

Variables declared within the scope or a particular block will only be recognized within the scope of the relevant course. In Java, a block begins with { and end with }. Consider the following code examples:

class variableScope {
   public static void main(String[] args) {
      int a = 10;

      if(a>5) { //start of block
          int b = 15;
         System.out.println("a value in if block: " + a);
         System.out.println("b value in if block: " + b);
      }  //end of block

      System.out.println("a value outside if block: " + a);
      //false
      //System.out.println("b value outside if block: " + b);
   }
}

The following result will be displayed on the screen:

a value in if block: 10
b value in if block: 15
a value outside if block: 10

In the code above, b variable declared inside if block that would not be recognizable from outside the block.