Read: 02 - Arrays, Loops, Imports

Packages and Import

• Package = directory. Java classes can be grouped together in packages
• A package name is the same as the directory (folder) name which contains the

Package declaration

Following the optional package declaration, you can have import statements

Default package. Altho all Java classes are in a directory, it’s possible to omit the package declaration. For small programs it’s common to omit it, in which case Java creates what it calls a default package.

The statement order is as follows. Comments can go anywhere.

• Package statment (optional).
• Imports (optional).
• Class or interface definitions.

Import

• import javax.swing.*; when write * all classes that located in swing available to use in another program.
• import javax.swing.JOptionPane; just JOptionPane method available in my program.
• javax.swing.JOptionPane.showMessageDialog(null, "Hi"); write packages name and the method in my code.

Common imports

• import java.awt.*; Common GUI elements.
• import java.awt.event.*; The most common GUI event listeners.
• import javax.swing.*; More common GUI elements. Note “javax”.
• import java.util.*; Data structures (Collections), time, Scanner, etc classes.
• import java.io.*; Input-output classes.
• import java.text.*; Some formatting classes.
• import java.util.regex.*; Regular expression classes.

Array

Using array to stored data in the one variable like int []arr= {'1','2','3'}; of string or numbered and can fixed and compared to returned the result like which value of these array is long length or odd even capital letter or small letter.

Loops

Type

• While loop => Have a condition, if condition is true login in the while if not don’t join the loops.
• for loop using almost to search in the array value or to entered value many time.
• Do-while => using to do something before see the condition is true or false.