mrloulass/java-notes

java-notes

Java Programs

• Java can be used to build:
  • Web applications
  • Mobile applications
  • Desktop applications
  • Web servers
  • Embedded systems

Java Development Kit (JDK)

• use for building and developing Java applications
• Includes the JRE and other tools to create Java programs

Java Runtime Environment (JRE)

• use for running Java applications
• has Libraries and classes
• JVM Java Virtual Machine

Java Virtual Machine (JVM)

• execute Java programs

Running Java code

• 1st: need to complied Java source code to Java byte code javac Filename.java
• 2nd: to run the code java FileName
• Anytime you change the source code you need to complied the code before you run the code.

Integrated Development Environment (IDE)

• is a software we can use to build and run Java programs
• Built for compiling and executing code
• has a Graphical User Interface (GUI)
• Contains built-in tools to make the development process faster
• Example:
  • IntelliJ IDEA
  • Eclipse
  • NetBeans

Input/Output

• Output using System.out.println() to the console
• Input using Scanner input = new Scanner(System.in) this allow the user to input information to the console;
  • Scanner is a class in java.util package used for obtaining the input of the primitive types like int, double, etc. and strings.

Control Flow

• A program's control flow is the order in which the program's instructions or code statements are executed.

Operators in Java

• Relational Operators
  • less than <
  • greater than >
  • equal to ==
  • greater than or equal to >=
  • less than or equal to <=
  • not equal to !=

Decision- making with if statement in Java

• An if statement is a control flow statement, where if the condition is true, it performs some kind of action

Understanding scope in Java

• The scope of a variable is the part of the program where a piece of code is accessible or in which it can be used
• Curly braces {} create different blocks or regions in Java

While Loop

• A while loop allows code to be executed repeatedly based on a Boolean condition

Debugging in Java

• involves locating and fixing a program's errors (bugs)

Print Statement

• use print statements to print the value of a given variable and follow the control flow of a code

Syntax Errors

• are misspelled variable or missing semicolon
• can cause your code to fail before it runs
• the code must be in the right format for a computer to read

Logical Errors

• deal with the logic of a program
• the program doesn't act as the user expects

IDE: Integrated Development Environment

• helps compile and run Java programs
• helps debug Java programs by detecting and revealing errors
  • Breakpoints: an intentional stopping point put into a program for debugging purposes. This allow us to inspect its internal state
    • click the line of code number and run the code in debug mode
    • internal state: variable values, the result of certain lines of code is executed ot not

Package

• organizing and group your classes together

Comments

• single line uses // in the begin
• multi line uses /*can add multi comments between */

Variables

• is a box that store data types

Data Types

Primitive Types

• Boolean: represent a true or false value (Ex: Is a light on or off)
• Int: represent a whole number (Ex: number of siblings)
• Double: represent a decimal number (Ex: your GPA 3.3)
• Char: represent a single letter or symbol (Ex: your First initial)

Reference Types

• String: a sequence of ordered characters (Ex: a word or person's name) or built out of characters
  • String value: will have quotation marks around it ("speaker")
  • String variable: string myFavoriteWord = "speaker"
  • String operation:
    • charAt: is a special string operation that allows us to access a character at a specific location within the string
      • variable.charAt(index)
      • Input: index of the wanted character
      • Output: the value of the character at the inputted index