Android Development - Part 2

Welcome video

Why android studio

IDE : integrated development environment
- it helps your while your coding
- give you feed backs
- it is fast because of the auto complete mechanism
- better to troubleshoot because of debugging feature
- i can change class name in all of my program easily, don’t need to search for each file

The best tool to develop your app

there are three ways to test your app
- first your can use emulator : has problems
- second use a physical device : better but have to test on specific number of device, depending on what you own
- use genymotion : best way

Files, packages, classes and methods

Java code components
- File
- class
- attribute
- methods

Syntax symbols

case of the writing : how you write variables or methods or any name
- camelCase : small first word camel and capital the second one Case
- PacalCase : capital each word

Method signature

there are five components for the java method signature
1. accessibility keyword, this defines what has access to this method
2. the return value type, even if there is no return value
3. method name, so we can call it
4. syntax symbols like parenthesis or braces
5. parameters, these are the inputs to the method

Data types and variables

attribute is in the beginning of the class
how to differentiate between class and method
- the class’s name followed by braces {}, it’s better to use PascalCase to define it
- the method’s name followed by parenthesis (), it’s better to use camelCase to define it

example of class, a private method and variables

// class definition
public class MyInfo
{
  // attributes
  int myAge = 33;
  String myName = "Ahmed";
  boolean isMale = true;
  char middleInitial = 'M';
  float myHeightInMeters = 1.6f;
  // method definition
  private void updateMyInfo ()
  {
    myAge = 35;
    myName = "Ahmed Khairy";
  }
}

Memory lockers

memory
reading, writing
pointers, that used when one location is not sufficient, so it give it the beginning of the memory that can be used

Introduction to computer memory

if we use pointer it won’t be known where is the end of that variable until we put \n that’s mean the end of that variable, the benefit of pointer that i can use data without copying it
there are two different data types
it is better to reduce the usable memory as possible

Reference and null

references are pointers
to define a reference you use : int[] new = new int [4];
- this code means that this is an int array called new and it reserves 4 places in memory each place is int data type
to assign value to each place : new [0]= 2;, and so one to new [3]
if i want to make reference but not giving it a memory we use : int [] new;, this declaration make the reference equal null
so for example if i create another reference : int[] new2; it’s value will be null
i can make the new reference points to the value of the first reference by writing : new2 = new;, but if i assign a null to new reference, the new2 still point to the same data

Android studio

installing android studio
sdk manager installing

Arrays

if i want to declare one int variable i can use int x, but if i want to declare array of int variables i can use int []

i can set array elements by

int [] myArray = new int [5];
myArray [0] =  0;
myArray [1] = 4;
etc ...

int [] myArray = {0,4,etc,...}; //the size of the array is defined depending on the elements

Lists

list types
- arraylist
- linkedlist
- vector
difference between array and list
- String[] days = {"sat","sun","mon","tue","wed","thur","fri"} : array
  - if i want to insert an element between them i have to create new array then take the elements before the inserted element then add the new element and take the other elements from the original array and so on
- ArrayList<String> myList = new ArrayList<String>(); : define a collection in java
  - if i want to add elements to that list i will use myList.add("first"); myList.add("second"); myList.add("fourth");
  - if i want to insert an element between them i will just use the index number and use add myList.add(2,"third");

Sets

it is used to store data that is unique and never duplicate
types of Sets
- hashset
- treeset
- linkedhashset

if i want to store data like

HashSet<String> mySet = new HashSet<String>();
mySet.add("one");
mySet.add("two");
mySet.add("three");
mySet.add("two"); // this won't be added, it will keep just one of them

Maps

it is used to give a key to an element instead of index number like

key >>>> value
0   >>>> "cat"
1   >>>> "dog"
200 >>>> "anything"

types of maps
- hashmap
- hashtable
- treemap

to declare a map

HashMap<String,String> myhashmap = new HashMap<String, String>();
myhashmap.put("mykey","dog"); //to put elements
myhashmap.get("mykey"); //to get it

to make a list of key maps

HashMap<String,HashMap<String,String>> newhashmap = new HashMap<String,HashMap<String,String>>();
newhashmap.put("USA",newhashmap);

Objects and ‘new’

java is an object oriented programming

differences between class and Object

public class MyClass  //this is class (blue print)
{
  String variable = "moose";
  public MyClass (String aString)
  {
    variable = aString;
  }
}

to get from a class to an object, we use the new keyword
- MyClass myObject = new MyClass();
- this will point to MyClass memory, it takes it’s blue print
if i use this command
- MyClass otherObject
- this will point to null
if i create an array of objects the inheret from MyClass
- MyClass[] someObjects = new MyClassp[5];
- all of them will point to null, i have to assign to each object like
  - someObjects[0]= myObject

Constructors and allocation

MyClass myObject = new Myclass();
- MyClass : is the class i want to make object from
- myObject : name of the new object
- new : keyword
but why is there a parenthesis?
- we use parenthesis when we deal with methods, but how ?
```
public class MyClass
{
  String memberVariable = "moose";
  public MyClass()
  {

  }
  public MyClass (String aString)
  {
    memberVariable = aString;
  }
}
```
- first and second methods are called constructors, because they are called when constructing the object for the first time
- even if we didn’t create them, they will be generated for us

Garbage collection and null

it is used to un allocate memories locations to free up spaces
java keep track of memory spaces and count how many times the program points to that location

Operators and assignments : bitwise and unary

The return statement

##The if statement