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