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Learning Java Notes

https://www.linkedin.com/learning/learning-java-4/downloading-java-on-your-computer

Intro

public class Main {  
 public static void main(String[] args) {  
  System.out.println("Hello World! It's me!");  
 }  
}
  • Compiling Java code 
javac code.java
  • Running it 
java code

Data Types

  • Java classifies different pieces of data with data types based on their value.
  • A data type provides a set of possible values.
  • If a piece of data is one of a data type’s values, it is classified as that data type.
  • Primitive Types are the foundation for all other data types within the Java programming language.
  • Boolean: represents a true or false value (for example, is a light on or off?)
  • Int: represents a whole number (for example, number of siblings)
  • Double: represents a decimal number (for example, your GPA)
  • Char: represents a single letter or symbol (for example, your first initial)
  • Reference Types
  • String: a sequence of ordered characters (for example, a word or person’s name) 
import java.util.Scanner;  

public class Main {  

    public static void main(String[] args) {  
        double studentGPA = 3.45;  
        String studentFirstName = "Kayla";  
        String studentLastName = "Hammon";  
        char studentFirstInitial = studentFirstName.charAt(0);  
        char studentLastInitial = studentLastName.charAt(0);  
        System.out.println(studentFirstName + " " +  
                studentLastName + " has a GPA of " + studentGPA);  
        System.out.println("What do you want to update it to?");  

        Scanner input = new Scanner(System.in);  
        studentGPA = input.nextDouble();  

        System.out.println(studentFirstName + " " + studentLastName +  
                " now has a GPA of " + studentGPA);  
    }  
}

Control Flow

  • A program’s control flow is the order in which the program’s instructions or code statements are executed.
  • All of the programs we’ve looked at so far execute one statement after another, sequentially.
  • Here is where explanations or definitions can go; try and keep each built two or three lines max.
  • We can manipulate which line of code is executed with special control flow statements and conditions.
  • A line of code might never be executed, be executed once, or multiple times.
  • The conditions determine how many times a given line of code is executed.

Scope with an If-Else Statement

if (inputtedNum < 100) {  
 int favoriteNumber = 5;  
 System.out.println(favoriteNumber);  
 favoriteNumber = 10;  
 System.out.println(favoriteNumber);  
 // In scope (accessible) for favoriteNumber  
} else {  
 // Out of scope (not accessible) for favoriteNumber  
}  
// Out of scope (not accessible) for favoriteNumber  

String favoriteFood = "pizza";  
// In scope (accessible) for favoriteFood  
System.out.println(favoriteFood);  
if (inputtedNum < 100) {  
 // In scope (accessible) for favoriteFood  
 favoriteFood = "chicken tacos"”;  
 System.out.println(favoriteFood);  
} else {  
 // In scope (accessible) for favoriteFood  
 favoriteFood = "steak";  
 System.out.println(favoriteFood);  
}  
// In scope (accessible) for favoriteFood
Last update : August 31, 2023
Created : August 25, 2022

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