Stephanie Chatagner's Blog

Well.

This week, it’s … Java. So, Go head!
Although this first day was quiet, the foundations of this language are laid! Object Oriented − In Java, everything is an Object:

• portable, statically typed, object-oriented programming language
• developed by Sun in the mid 1990s
• useful for web pages and mobile apps or for the needs scalability, performance, multithreading, memory management and portability
• From C and C++

Here, I found help in my Java path:
Java Tutorial (English)
Achref El Mouelhi (French)

Major Building blocks

• Keywords : predefined words of the Java language
• Variables : to store data
• Loops: to iterate over data structures
• Methods : to write a block of code once that we can then re-use many times
• Access Modifiers: to restrict access to variables and methods
• Javadoc : JavaDoc produces a searchable HTML document that defines the classes and interfaces of an application
• Arrays : to easily and efficiently store and retrieve collections of data

Java Keyword

• Keywords are simply words that have a predefined meaning in the Java language.
• used for some internal process or represent some predefined actions.
• these words already have a meaning in Java, so they are reserved.
• not allowed to use as a variable names or objects.

Variables

• A variable is a combination of:
  • A location in the computer’s memory and
  • An associated name that we can use in our code to refer to the data in that memory location
• Static Typing
  • The data type is attached to the variable when it is first declared
  • The data type is checked when the code is compiled
  • The data type for a variable cannot later be changed
  • ; : end of the statement
• Primitive vs Reference
  • primitive : a value, by itself type name = value; lowercase char name = 'value' ; !!!! simple quote
  • reference value : refers to an object stored in another location in memory, with data object Type name = value; uppercase
    • String name = "few words" ; !!!! double quote
    • Types are String or Array, methods attached to accss and manipulate the data they contain text.length();, can be customized
    • user-defined classes
• Type Casting
  • change type in another type
    • Automatic : converts a smaller type into a larger type

        int intNumber = 3;
        double doubleNumber = intNumber;
      

    • Manuel : Convert a larger type into a smaller type, Convert one object type into another.

        double doubleNumber = 3.5;
        int intNumber = (int)doubleNumber;
      

    • Truncation : loss precision

Methods

• block of code to re-use
• calling or invoking the method
• Syntax : Name, Parameters, Method body, Return type
• Methods vs Functions:
  • A function is any block of reusable/callable code
  • A method is a block of reusable/callable code that is attached to a class or object

      public class MethodExercise{
      public static void main(String[] args) {
          System.out.println("The Sum is:" + MethodExercise.addNumbers(7,7));
      }
    
      //Add your function here:
      public static int addNumbers(int num1, int num2){
              return num1 + num2;
      }
    

• Stack vs Heap
  • two different memory regions
    • Stack used to store primitives and object references //pile
      • Items get added and removed as a given method executes
      • can only be accessed by the related method
      • removed from the stack in a Last-In-First-Out (LIFO) order: last element added to the stack is the first that gets popped off the stack
    • Heap is used to store the objects themselves //paquet
      • objects stay until the application is done or no object references using them
      • accessible from anywhere in the program
  • determine how other classes are allowed to access your variables and methods.

Access Modifiers

• restrict access to certain data in the application in order to ensure it doesn’t get modified
• Access modifiers determine how other classes are allowed to access your variables and methods.
• Type of Access Modifiers:
  • Public : the class can be accessed from everywhere. expose a method to all other classes.
  • Private : only the defining class can access the data. This provides security, by not allowing other classes to change the data directly. changes the data via the provided methods only.
  • Protected means that access is restricted to the defining class, package, or subclass. useful with subclasses and inheritance. allow subclasses to use variables and methods from the parent class.

  • Default means access is restricted to the defining class or the package. used when classes inside the same package that we may want to expose data and methods too.

    Access Modifiers on Methods
    private void methodName()
void methodName() // The default is no access modifier

    Access Modifiers on Variables
    private int number;
int number3; // Default is no access modifier

Array

• fixed-sized data structure =⇒ on ne plus rajouter d’element. seulement modifier
• to store multiple values same value
• array element be accessed by array index
• int [] numbers = {1, 2, 3, 4}; create an array
• int variable =numbers[1] access te array
• Create array

    int [] numbers =newint[4]; // init array, empty
    numbers[0] = 1; // assign values
    numbers[1] = 2;
    numbers[2] = 3;
    numbers[3] = 4;
  

• Loop over array

  Loops

  Components of a loop: Initialization, condition, execution body, increment or decrement

  while Loop: continuously executes as long as a given condition is True.

    while(condition){
        Execution block
    }
  

  for Loop: iterates over the execution blocked until condition is met

    for(initialization; condition; increment or decrement){
        Execution block
    }
  

  do while Loop: runs the wxeption block first the evluates the condition to determine if it shoulld continue to iterate

    do {
     Execution block
    } while(condition);
  

  Even if the condition is false right from the start, the code inside the loop will still get run once.

So, step by step and keep learning!