8/22/2019 Package Java
1/3
JAVA: Creating a Simple Package
Packages are the libraries in Java. They can be either
pre-defined or user-defined. Creating
packages follows a very simple mechanism. It is possible to use
to include the same package
command in more than one Java source file to indicate that all
such classes belong to the samepackage.
The following example shows how to create a simple package that
has only one class. This classhas only one method test() whose
objective is to determine if a given string is a palindrome or
not. A palindrome as it is known is a set of characters that
reads the same both ways. For
instance, ABBA is a palindrome.
This class is created under the mypackage package. This package
later is imported in another
class that is shown in a further example to make use of the
method test().
package mypackage;
public class Palindrome
{
public boolean test(String str)
{
char givenstring[];
char reverse[] = new char[str.length()];
boolean flag = true;
int count = 0, ctr = 0;
givenstring = str.toCharArray();
for(count = str.length() - 1; count >= 0; count++)
{
reverse[ctr] = givenstring[count];
ctr++;
}for(count = 0; count < str.length(); count++)
{
if(reverse[count] != givenstring[count])
flag = false;
}
return flag;
}
}
Save the code as Palindrome.java in the current working
directory. Compile the program usingthe following command:
javac -d . Palindrome.java
8/22/2019 Package Java
2/3
It must be noted that there must be space before the . (dot) and
another space after the dot. This
creates a folder called mypackage in the current working
directory and the class file is stored in
mypackage directory.
The CLASSPATH must be set to the current working directory so
that the user-defined packages
(class files) are available for use. Now that the package is
created, it can be used in any Javaprograms. The import statement
is used to include the newly created package in a program. This
is illustrated in the next example:
import mypackage.*;
class Palintest
{
public static void main(String args[])
{
Palindrome objPalindrome = new Palindrome();
System.out.println(objPalindrome.test(args[0]));
}
}
In the above example, the user defined package is imported just
as Javas built-in packages wereimported. An instance of Palindrome
class is created since the method test() is not static. If the
method test() was declared static then the method could have
been invoked using only the class
name and there would have been no need to create an instance of
the class. The method test() is
used just like any other built-in method.
When a java program is executed, the JVM searches for the
classes used within the program on
the file system. Java uses one of the two elements to find a
class:
The package name The directories listed in the CLASSPATH
environment variable.
It must be noted that you must ensure that the Palindrome.java
file is not located in the samedirectory as the Palintest.java
file. The Palindrome.java file can be moved to the package
folder
mypackage.
The output of the above folder is:
The Palindrome.class file is located in the mypackage
folder.
Thus this can be concluded that the user-defined package
mypackage can serve as a library for
any other class.
