Read: 02 - Arrays, Loops, Imports

Packages and Import

• package is collection of classes grouped together.
• the package name should be the same as the parent directory.

Package declaration

• package decleration is on top of the file before any thing and it’s optional.
• below it i can import stuff and thse statements allow me to use classes from other packages.

Package declaration syntax

• to declare a package first i type package packageName;.
• Imports comes after package decleration.
• then i can define class to work on.

Imports

• i have 3 ways to import classes.
  • USING WILD CARD.
    • import java.swing.*; this line of code uses wild card star which means import everything, but hey i can only use 1 class.
  • using class name.
    • i import it similar to wild card but with name import java.Math;.
  • declare and use it inside code.
    • javax.swing.SomeMethod();.

Common imports

most imported packages are:

• 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.

Loops

• loop statement can interpret and altr the normal flow of the program.
• loop statement allow me to run piece of code more than once.
• There are 2 types of loops for loops and while loops.

for loops:

• i use for loop when i know the end of the loop (or at least i can the program), for example i give user 5 attempts to enter correct password.
• syntax for(int i= 0; i<5; i++){ code statements here….};
  1. first part: is the loop start and current iterate number, and it will always compiler read it first.
  2. second part: as long as the comprasion operator evaluate to true the code inside braces will run, and it get’s executed 2nd.
  3. third part: when the current round is finished this block get executed.
• important note about for loop: first part and second part will be executed before the loop start, and third part will be executed after the round finished.

#### While loop and do white:
  * I use it when I don't know how many times i need to iterate, for example a user want to enter password.
  * syntax  `while(condition) {code ....};`
  * as long as the condition evaluate to true, the while loop keep running.
  

2.1 do while:
  * It's the while loop but do while exist because i might want to execute code inside at least once.
  * syntax:  `do { code ...} while(condition);`


### Branching Statements
#### break
* break is used when i want to break the iteration statement before it's finished based on a condition.
* so basically let's say my for loop will iterate 50 times, and i tell it to exit loop if it exceed 20 times.
* example:

for(int i=0; i<5; i++){ if(i>2){ break; // loop when i = 0, 1,2 }; };

#### continue:
* i use it when i want to skip executing code based on condition, for example i want for loop to keep iterating to the end, but on 5th iteration it should not execute.
* example:

for(int i=0; i<5; i++){ if(i>2){ continue; // skip executing when i > 2 }; };

## Arrays
* Arrays are variables container, that means it contain more than 1 variable.
* it contains as many variables as i store in it.
* java start assigning indexes from 0, meaning when i have array of size 5 data will be stored at indexes from 0 to 4 (count them it's 5).
* to refer to a variable or target a variable i have to use indexes.

* to declare an array I should use following: 
  * int[] arr;
* to make an array with specific length: 
  * int[] arr = new int[5];
* to get the length of array i use property
  *  arr.length;
* **shortcut**, i can create array and assign values to indexes at the same line.
     int[] arr = {1,2,3,4,5,6};

#### forEach:
  * it's a shorthand version of for loop.
  * it's used when i want to iterate over array.
  * for (int element : arrName){ execute code on element};
  * example :

int[] nums = {1,2,3,4,5};

for (int num : nums){ System.out.println(num); };