Reading-notes

Arrays, Loops, Imports

Packages and Import :

-packages its the same of “directory”. A package is a single folder (directory) containing a group of related classes (.java files) and interfaces.

• Import statments allowed you to name the packages from other libraries .

Package declaration :

-A package declaration, if used, must be the first thing in the file, and describes the folder in which it occurs.

Package declaration syntax:

• The statement order is as follows. Comments can go anywhere.
  1. Package statment (optional).
  2. Imports (optional).
  3. Class or interface definitions.

Imports: three options:

if we take an example to see what the three options , we have JOptionPane class , this class located in the swing package which is located in the javax package.

The wildcard character (*) is used to specify that all classes with that package are available to your program:

• import javax.swing.*; // Make all classes visible altho only one is used.

Classes can be specified explicitly on import instead of using the wildcard character: -import javax.swing.JOptionPane; // Make a single class visible.

Alternately we can the fully qualified class name without an import like in this ex :

• class ImportTest { public static void main(String[] args) { javax.swing.JOptionPane.showMessageDialog(null, “Hi”); System.exit(0); }}

Common imports :

Java 5 added an import static option that allows static variables (typically constants) to be referenced without qualifying them with a class name.

A Guide to Java Loops :

• Types of loops that we can find in Java:
• Simple for loop
• Enhanced for-each loop
• While loop
• Do-While loop

for-loop :

• an entry-controlled loop that facilitates a user to execute a block of a statement(s) iteratively for a fixed number of times.

while loop :

• a control flow statement that allows code to be executed repeatedly based on a given Boolean condition.

Do-While Loop :

• is used to iterate a part of the program repeatedly, until the specified condition is true.