Variables and Methods

Variables:

Variable is a name given to a memory location in which, we can store some value which can be used in a program.

Variable Declaration: It is process of specifying what type of data to be stored into the memory location.

              Syntax:     datatype <variable_name>  OR datatype <var1>, <var2>, <var3>

Ex: 

                          int age;  (age is a variable name given to a memory location where we can store integer type of data)

                          float marks;

                          char c;

                          boolean status;

 

1. A Java program can contain any number of variables.

2. In java language, the variable must be first declare then use it. We cannot use the variable without declaring it.

Rules in a variable Declaration:

·         A java program can contain any number of variables

·         The declaration of the variable is dynamic that means we can declare a variable anywhere in a program.

·         The variable in java language must be first declare and use. (java is strongly typed language)

·         When a variable is declared, the memory for that variable is allocated depending upon the data type that is specified

·         Once a variable is declared, the memory for that variable will be allocated and the variable will be automatically initialized with the default value of that corresponding data type.

Data Type                    Default Value            Data Type                     Default Value

  byte                ->                  0                           float                                    0.0

  short               ->                  0                           double                                0.0

  int                  ->                   0                           char                                    space

  long               ->                   0                           boolean                               false

 

              The default data type under integer category is “int”. The default data type under floating point category is “double”.

              If a variable is declared and if we do not provide any value, then that variable will be automatically initialized with the default value.

 

Declaring and Initializing a Variable:

              The variable can be initialized with our own values at the time of declaration.

Syntax:

          datatype <variable_name> = <value>;                     (OR)

          datatype <variable_name1> = value1, <variable_name2> = value2  so on……

Ex:    int a = 12;        OR      int a=10, b=20, c=30;

Initialization: The process of providing a value to the variable for the first time is called a initialization.

Assignment: The process of providing a value to a variable second time onwards is called a assignment.

              The value of a variable can be changed during the execution of a program that a variable can be assigned any number of times but variable can be initialized only one time.

              Ex:       int a=10;          // Initializing

                          int a=20;          // Assigning

Note: We can also call a value as a literal.

                          int a = 10;                    // 10 is integral literal

                          float b = 12.2               // 12.2 is floating point literal

                          char c = ‘$’                  // $ is character literal

Method: A method is a block of code that perform some task or an action.

JVM executes a method only when we call or invoke it.

We write a method once and use it many times. We do not require to write code again and again.

A method must be declared within a class.

A method can be called any number of times.

Method Creation Syntax:

              <access specifier> <return type> <method name>(parameters list){

            //Method body

}

Example of Method Creation:

public void addition(int a, int b) {

           System.out.println(a+b);

}

A method contains Two parts. Method Header and Method Body. Method header contains 4 components those are access specifier, return type, method name and parameters.