reading_notes
Read: 02 - Arrays, Loops, Imports
Java Imports:
A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. Packages are divided into two categories:
Built-in Packages (packages from the Java API) User-defined Packages (create your own packages)
package declaration syntax:
- Package statment (optional).
- Imports (optional).
- Class or interface definitions.
import options:
* import javax.swing.*; // Make all classes visible altho only one is used.
* import javax.swing.JOptionPane; // Make a single class visible.
* Alternately we can the fully qualified class name without an import.
Common imports:
There are 166 packages containing 3279 classes and interfaces in Java 5. However, only a few packages are used in most programming. GUI programs typically use at least the first three imports.
| import type | used for |
|---|---|
| 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. |
Different types of loops in Java:
In programming languages, looping is a feature which facilitates the execution of a set of instructions until the controlling Boolean-expression evaluates to false.
Types of loops:
- Simple for loop: control structure that used to repeat certain operations by incrementing & evaluating a loop counter.
- Enhanced for-each loop: It provides an alternative approach to traverse the array or collection in Java
- While loop: It repeats a statement or a block of statements while its controlling Boolean-expression is true.
- Do-While loop: looks like while loop but the first condition evaluation happens after the first iteration of the loop.
