Introduction to Packages in Java

      Packages are containers for classes.We can define  classes inside a package that are not accessible by code outside that package.A package can be defined by including a package command as the first statement in the Java source file.Any classes declared within that file will belong to the specified package.The package statement defines a namespace in which classes are stored.If we omit the package statement,the class names are put into the default package,which has no name.
     General Form:
               package package_name ;
      Example:   package MyPackage ;
      which creates a package called MyPackage.Java uses the file system directories to store packages ,that is the class file for any classes that declared to be a part of MyPackage and must be stored in a directory called MyPackage.The directory name must match the package name exactly.More than one file can include the same package statement.We can create a hierarchy of packages.To do so simply separate each package name from the one above it by use of a period.The general form of a multilevel package statement is ;
                                        package pkg1.[pkg2.[pkg3]] ;
         A package hierarchy must be referred in the file system of the Java Development System,
                                        package java.awt.image ;
        needs to be stored in the java\awt\image
Example program:
        
      package MyPackage;
      class Balance 
      {
                  String name;
                  double bal;
                  Balance (String n,double b)
                  {
                               name = n;
                               bal = b;
                               show( );
                  }
                  void show( )
                  {
                               if(bal > 0)
                               {
                                              System.out.println("Name = "+name+"  balance = "+bal);
                               }
                               else
                               { 
                                              System.out.println("Name = "+name+"  balance = ----");
                               }
                  }
      }
      class AccountBalance
      {
                  public static void main(String args[ ])
                  {
                              balance current[ ] = new Balance[3];
                              current[0] = new Balance("John",123.25);
                              current[1] = new Balance("Jack",155.99);
                              current[2] = new Balance("Tom",160.00);
                  }
      }
OUTPUT
     Name = John Balance = 123.25
     Name = Jack Balance = 155.99
     Name = Tom Balance = 160.00