• Java is a common language. 
• It is class based, unlike Python, which is interpretive. 
• This means that everything needs to be in a class. 
• The class name has to be the same name of the file. 
• Don't forget the semi colons! 

CODE

System.out.println("Hello World!");

public class HelloWorld {
    public static void main(String[] args){
        
       System.out.print("Hello World!");

    }
}

1. If System.out.println is used after System.out.print: the next text will be printed on a new line. 
2. If System.out.println is used after System.out.println: the next text will be printed on a new line. 

• Enclose a string.
• String: a specific order of characters. 
• Must include, or else IDE won't understand.

• Boolean variables: true/false. 
  i.e: true, false, yes, no
• Int: numbers, specifically integers & whole numbers
  i.e: phone numbers, years, id numbers, percent grades
• Double: floating point numbers, i.e. decimals. 
  i.e: pi, division, money, scores
• String: order of specific characters 
  i.e: names, notes, addresses, places

Code

public class StudentInfo {
    public static void main(String[] args){

        String name = "Adhithi";

        double avgGrade;       
        avgGrade = 97.90;

        final int numClass;        
        numClass = 5;

        boolean atDelNorte;        
        atDelNorte = true;

        System.out.print(name + "has an average grade of " + avgGrade);
  
        System.out.println(name + "is taking " + numClass + " classes."); 
                     
        System.out.println(name + "is currently at Del Norte for the 2021-22 school year: " + atDelNorte);

    }}

• This code includes all the variables and data types discussed.
• Do you think you can make your own, in a different scenario?
• What are some scenarios you could use this for? Try coding it! 

• + is addition 

• - is subtraction 

• * is multiplication 

• / is division 

• % is modulus

1. Int <operation> Int -> Int 
2. Double <operation? Double -> Double 
3. Int <operation> Double -> Double

• You can't divide by 0; that will result in an error. 
• You can create compound expressions.

7 = x; 

x = 7;

Code: 

public class HelloWorld {
    public static void main(String[] args){
        double scoreOne;         
        scoreOne = 90;    
            
        double scoreTwo;         
        scoreTwo = 94;

        double scoreThree;         
        scoreThree = 99;

        double average;         
        average = (scoreOne + scoreTwo + scoreThree)/3;

        System.out.print(average);
    }
}

• Why are we using double instead of int? 
• Could you think of any other scenarios we could use? 
• RogerHub uses similar algorithms and code to calculator your grade for you. 

• The operator will come in front of the equal sign. 
• To add to the variable: += 
• To subtract from the variable: -=
• To multiple from var: *=
• To divide from var: /=
• To mod from var: &=

x++; 

• Used to change data types 
• Casting operators - two types 
• To change a double to an int: (int) 
• To change an int to a double: (double) 
• You can use rounding here as well 
• Note: Integers have limit of digits that can be used 

double x; 
(int) (x + 0.5);

double x;
(int) (x - 0.5);

Code

1. Where would you need to cast or round something? 
2. Code a program that you could use for the above scenario. 

double fact1 = 1/2;

1. Note down CB Talk 1.2, Variables and Data Types 
2. Pay attention to calculations, which are done from left to right 
3. Make sure to note which values are integers and doubles 

• Java is an object oriented programming language (oop). 
• A class can be used to define new data types or create blueprints for objects. 
• An object is created from a class, resulting in an instance of a class. 

• What attributes does your class have?
•  If you did a class that was identity, you might have their name, email, phone number, id, etc. 

CODE

public class DogTester{

Dog graceDog = new Dog("Grace", "lab", 1);
graceDog.bark();

}

• What are some other classes you could create? 
• What do you think you could use it for? 

• Constructors are used to initialize the attributes for the object. 
• Think of init.py and init in python. Similar idea here. 
• We can have more than one constructor per object. This is called overloading the constructor. 
• A no argument constructor has no parameters and sets the instance variables for the object to default values.

CODE 

public Person(string nm, int ag, boolean ad)

• These are our parameters. Parameters are characteristics that define our class. 
• How many parameters are there here? 
• What are the parameters? 
• Can you think of a class, and include your own parameters?

(string nm, int ag, boolean ad) 

Dog graceDog = new Dog("Grace", "lab", 1);

• Dog is the name of the class.
• graceDog is the name of the new value. 
• new indicates we're going to create a new value. 
• Dog is the class, and within that we're including our parameters. 

• We went over procedural abstraction briefly, for those of you coming in from CSP. 
• Instead of rewriting the same code for each thing we want to do, we compile our algorithm into a procedure. 
• This procedure can be called in place of the repetitive code. 

CODE 

• Sometimes, we want to compare two numbers or see if two things are equal. 
• To do this, we use boolean expressions, which represent logic and tell whether something is true or false. 
• These are the two values that boolean primitive types can take. 
• There are several operators that can be used to create boolean expressions. 
• Any statement containing these operators will result in a boolean. 

• == equals to (two primitive types have the same value)
• != checks for inequality (not equal)
• < less than
• <= less than or equal to
• > greater than
• >= greater than or equal to

CODE 

• Sometimes, we want our code to perform an action only if a certain condition is met (eg. the integer is even), while other conditions result in different actions. 
• This will take a conditional statement to run. 
• These usually consist of a conditional statement header with the in it condition and a body that includes the code that is run if the conditional statement header is true.

if (x > y){ 
result = x - y;
System.out.print(result);
}

CODE 

if (x % 2 = 0) { 
System.out.print("This number is even.");
} 
else if (x % 3 = 0) { 
System.out.print("This number is divisible by three.");
} 
else {
System.out.print("Try again")'
}

• We have just covered if statements, but what if we want something to be done if the condition that we are checking is false? 
• This is where the else statement comes into play. 
• The header for the else does not have a condition and is just "else" while the body is what is performed if the condition for the if statement is false.
• Together, these create an if-else statement, or a two-way selection. 

if (x>y) { 
System.out.print("x is greater than y.");
} 
else {
System.out.print("x is not greater than y.");
}

• Repetition of statements 
• While helps for repeating a process if a certain condition is true. 
• A loop is an infinite loop when the Boolean expression always evaluates to true. 

• Setting a song to repeat 
• shampoo instructions 
• cooking recipe 

• initialization - should a var start at 1 or 0? 
• boolean expression - is it just greater than or greater than or equal to? 
• update - should the value increase or decrease by one each time? 

• String.substring method: retrieves particular portion of string. 
  • last 4 digits of credit card 
• String.equals method: compares the content of two strings. 
  • if password entered matches database. 
• String.length method: returns the length of a string. 
  • to see if new password fits length requirement. 
• for loop: allows us to repeat task. 

• A strong example is like a clock. Minutes, Seconds, Hours, etc. 
• When a loop is inside another loop, that inner loop must go all the way through the iterations before the outer loop can keep going.