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Tutorial 2 - Basic Java Syntax and Semantics

 

Basic data types

 

 

Data Type Wrapper Class Size Value range

byte

java.lang.byte 8-bit (1-byte)

-128 to127

short

java.lang.Short

16-bit (2-byte)

-32,768 to 32,767

int

java.lang.Integer

32-bit (4-byte)

-2,147,483,648 to 2,147,483,647

long

java.lang.Long

64-bit (8-byte)

-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

float

java.lang.Float

64-bit (8-byte)

4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative)

String (object)

java.lang.String

Unlimited

 

char

java.lang.Character

16-bit (2-byte)

0 to 65,535

boolean

java.lang.Boolean

8-bit (1-byte)

true and false



When we declare a variable we assign it an identifier and a data type.

For Example
String message = “hello world”

In the above statement, String is the data type for the identifier message. If you don’t specify a value when the variable is declared,

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> ;    

          ....;      

          ....;

    }



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