1. Software Development Packages
Computer Science 209
Software Development
Packages

2. What Is a Package?
A package organizes related resources (interfaces and classes) into a conceptual unit
Like a module in other languages
Examples:
java.lang (basic Java resources, no need to import)
java.util (scanners, collections, arrays, random numbers)
java.io (I/O, file processing)
javax.swing, java.awt (GUIs)

3. Using a Package: Typical Imports
import java.util.Scanner;
import java.util.Arrays;
public class CircleArea{
public static void main(String[] args){
int[] numbers = new int[3];
Scanner input = new Scanner(System.in);
for (int i = 0; i < numbers.length; i++)
numbers[i] = input.nextInt();
Arrays.sort(numbers);
for (int n : numbers) System.out.println(n); }
Bring in specific classes only

4. Using a Package: Fully Qualified Imports
import java.util.Scanner;
import static java.util.Arrays.sort;
public class CircleArea{
public static void main(String[] args){
int[] numbers = new int[3];
Scanner input = new Scanner(System.in);
for (int i = 0; i < numbers.length; i++)
numbers[i] = input.nextInt();
sort(numbers);
for (int n : numbers) System.out.println(n); }
Bring in specific classes and static methods only

5. Using a Package: The Wildcard Gets All
import java.util.*;
public class CircleArea{
public static void main(String[] args){
int[] numbers = new int[3];
Scanner input = new Scanner(System.in);
for (int i = 0; i < numbers.length; i++)
numbers[i] = input.nextInt();
Arrays.sort(numbers);
for (int n : numbers) System.out.println(n); }
Bring in all classes with wildcard

6. Using a Package: No Imports Needed
public class CircleArea{
public static void main(String[] args){
int[] numbers = new int[3];
java.util.Scanner input = new
java.util.Scanner(System.in);
for (int i = 0; i < numbers.length; i++)
numbers[i] = input.nextInt();
java.util.Arrays.sort(numbers);
for (int n : numbers) System.out.println(n); }
Use fully qualified names with no imports

7. Packages and Files
In Python, a module is typically a single file, which may define several related classes
In Java, a package is a directory, which may include several related classes in source code files and byte code files

8. File Organization within a Package
Source files for classes should be in a directory whose name is the package name
When byte code is generated, it is placed in a directory with the package’s name
These directories should be just below the directories of the source or byte code files that use them

9. Example: The Student Class
studentexample
StudentTester.java
StudentTester.class
student
Student.java
Student.class

10. Defining a Package Define Use package student; public class Student{
// Blah blah blah }
Use
import student.Student;
public class StudentTester{
// Blah blah blah }

11. Creating a Package from the Terminal
Place the .java files in a directory whose name is the package name
Attach to this directory and run javac *.java
Place the package directory in the directory where your client program will be
Run javac or java from this client program’s directory as needed

12. All Classes in One Package
student
StudentTester.java
StudentTester.class
Student.java
Student.class

13. Defining a Package Define Use package student; public class Student{
// Blah blah blah }
Use
package student;
public class StudentTester{
// Blah blah blah }

14. Compile and Run
> cd student
> javac *.java
> java student.StudentTester
Need qualified name to locate main class within package