Basic data types

it will be assigned the default value for its data type.

Identifier Naming Rules

• Can consist of upper and lower case letters, digits, dollar sign ($) and the underscore ( _ ) character.
• Must begin with a letter, dollar sign, or an underscore
• Are case sensitive
• Keywords cannot be used as identifiers
• Within a given section of your program or scope, each user defined item must have a unique identifier
• Can be of any length.
  
  Example:
  
  public class Main
  {
  
        /**
         * @param args the command line arguments
         */
      public static void main(String[] args)
        {
           // TODO code application logic here
           int iCount; //declaring an integer variable
           char cLetter; //declaring an charecter variable
           iCount = 10;
           cLetter = 'L';
           String strName = "Easy Steps";
           System.out.print(strName);
          }
  
  }
  
  User Defined Java Data Types
  
  Class
  

  Primitive data types are not sufficient. In the real world, we have much more complicated objects. Object oriented programming allows us to model real-world objects. User defined classes combine the data and methods that operate on that data.

• Class is a collection of member variables of primitive and/or composite data types and member methods or functions capable of accepting argument(s) of different primitive and/or class types. Each method can either return a value of specified return data type or no output value as indicated by void.

  Advantages:
  
  
• Class is responsible for the validity of the data.
• Implementation details can be hidden.
• Class can be reused.
• The client of a user-defined class is the program that instantiates instances of that class, and calls the methods of that class.
  
  Data within user-defined classes should be private to that class, and clients of that class should use the setter and getter methods to access that data.

  
  
  Syntax:
  
  Class
  {
           instance variable1;
  
  …
  
  …
  
           instance variableN;
  
           method(parameter-list1)
  
  {
  Method1 body;
  Return …;
   }
  
  …
  
  …
  methodZ(parameter-listZ)
  {
  MethodZ body;
  Return …;
   }
  }
  
  

  Access modifiers control access to this class. There are many ways in which a class can be accessed, such as:

  
  
  
• Methods of the user-defined class.
• Methods of other classes, outside of the user-defined class’s package.
• Methods of subclasses that inherit the user-defined class.
• Methods of classes in the same package.
  
  Access modifiers:
  
  
• public – methods of the same class and methods of other classes.
• private – methods of the same class only.
• protected – methods of the same class, methods of subclasses, and methods of classes in the same package.
• none – methods in the same package only
  
  Example:
  
  public class Bicycle
    {
      // the Bicycle class has three fields
      public int cadence;
      public int gear;
      public int speed;
      // the Bicycle class has one constructor
      public Bicycle(int startCadence, int startSpeed, int startGear)
        {
            gear = startGear;
            cadence = startCadence;
            speed = startSpeed;
        }
       // the Bicycle class has four methods
      public void setCadence(int newValue)
       {
            cadence = newValue;
        }
       public void setGear(int newValue)
        {
            gear = newValue;
        }
       public void applyBrake(int decrement)
        {
            speed -= decrement;
        }
       public void speedUp(int increment)
        {
            speed += increment;
        }

    } Structure
  
  Program Execution Control Statements
  
  Selection Statements
  
  if statement
  
  

  This is to execute a single statement or a block of code, when the given condition is true

   and if it is false then it skips if block and rest code of program is executed.
  
  

  Syntax:
  
  if(conditional_expression)
  {
  
       
        ;
        ...;
        ...;
  
  }
  
  Example:
  
  public class Main
  {
      public static void main(String[] args)
       {
         // TODO code application logic here
         int n = 10;
         if(n%2 == 0)
           {
             System.out.println("This is even number");
            }
        }
   }
  if-else statement
  
  The "if-else" statement is an extension of if statement that provides another option when

  'if' statement evaluates to "false" i.e. else block is executed if "if" statement is false.
  
  Syntax:
  
  if(conditional_expression)
  {
  <statements>;
  ...;
  ...;
   }
  else
  {
  
       <statements> ;    

        ....;      

        ....;

  }