Declaration of a Variable

(When you read about objects, you will find that objects of a particular type do consist of varying numbers of bytes. Ignore this for now.) Here is a program that uses the variable payAmount.

class example
{
  public static void main ( String[] args )
  {
    long payAmount = 123;    //a declaration of a variable

    System.out.println("The variable contains: " + payAmount );
  }
}

The line   long payAmount = 123;   is a declaration of a variable. A declaration of a variable is where the program says that a variable will be needed. For our small programs, declaration statements will be placed between the two braces of the  main   method.

The declaration gives a name and a data type for the variable. It may also ask that a particular value be placed in the variable. In a high level language (such as Java) the programmer does not need to worry about how the computer hardware actually does what was asked. If you ask for a variable of type long, you get it. Details like bytes and memory addresses are up to the Java compiler.

The declation in the example program requested a 64 bit section of memory which will use primitive data type long and will be named payAmount. Initially, the variable will have the value 123 stored in it. The compiler and java interpreter will (later on) make sure that this happens.

A variable cannot be used in a program unless it has been declared. A variable can be declared only once.