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6.2 PACKAGES IN JAVA
                 A package is like a folder in a computer where we can store similar types of files and sub-folders. In the same way,
                 a package in Java can store similar types of Java classes and packages. A package inside another package is known
                 as a sub-package.

                 Each class within a package can use the public properties              Definition
                 and behaviours of other classes. This saves time and effort,   A package is  a collection  of Java classes and
                 making the program efficient. A package is also helpful in   other packages having similar functionality.
                 resolving any issue related to naming conflicts if a class has
                 the same name as any predefined Java class.
                 For example, if you define a class named Date, there might be a naming conflict if your code imports java.util.Date.
                 However, if you place your Date class in a package, you can avoid this conflict by using the fully qualified name, and
                 the Java compiler will recognise it as distinct from the Date class in the Java class library.


                 6.2.1 Built-In Packages in Java
                 The packages that are already defined in the Java class library are called built-in packages. Java has a set of built-in
                 packages that are available to use without writing long codes. These packages contain several built-in Java classes
                 in them. Some of the built-in packages are:


                                                                 JAVA





                                    util          lang            io           swing           sql


                 Using the Built-in Packages
                 Suppose you want to use the Calendar class of the java.util package in your program, then you can use it the
                 following way:

                    java.util.Calendar obj = java.util.Calendar.getInstance();
                 Calendar is an abstract class of java.util package, hence it cannot be directly instantiated. You need to use the
                 getInstance() method to create an instance of the Calendar class. The drawback of using the built-in class in this
                 manner is that you need to type the complete hierarchy of the class each time when you want to use the class. So,
                 this process is very time consuming and it makes the program difficult to understand. To overcome this problem,
                 Java provides the import statement to use a class of a package in your program. The syntax of the import statement
                 is:

                    import <package-name>.<subpackage-name>.<class-name>;
                 Where, import is the keyword, <package-name> is the name of the package  <subpackage-name> can be the name
                 of any sub-package under the package and <class-name> can be the name of a particular class which you want
                 to import in your program. Similar to any other Java statement, every importing statement should be terminated
                 by placing a semicolon at the end of each statement. For example, if you want to import the Calendar class of the
                 java.util package, then:

                    import java.util.Calendar; //Importing the Calendar class of java.util package
                 Preceding statement imports only the Calendar class and its variables and methods. If you want to import all the
                 classes form a package, you just need to use the * (asterisk) symbol with your package name. For example,

                    import java.util.*; //Importing all the classes of java.util package


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