Unit 1

int, boolean, char, and double are primitives
Strings and other classes are objects
Compare primitives with == and objects with .equals()
Objects have properties while primitives do not
casting is when you assign a value of one primitive data type to another type. In integer division, the decimal is truncated. You need to use a double in order to keep the decimal
casting rounds down while Math.round rounds to the nearest int

int a = 7;
int b = 3;

System.out.println(a/b);
System.out.println((double)a/(double)b);

2
2.3333333333333335

@Type(type="json")
@Column(columnDefinition = "jsonb")
private Map<String,Map<String, Object>> stats = new HashMap<>(); 

public Integer height;

public Integer weight;

// Constructor used when building object from an API
public Person(Integer weight, Date dob) {
    this.height = height;
    this.weight = weight;
}

test this

4
3

They are both true

They are both true once again

11

no object needed

test output

@Type(type="json")
@Column(columnDefinition = "jsonb")
private Map<String,Map<String, Object>> stats = new HashMap<>(); 

public Integer height;

public Integer weight;

// Constructor used when building object from an API
public Person(Integer weight, Date dob) {
    this.height = height;
    this.weight = weight;
}

Concatanation is when you combine primatives together. For example, you would use the .append for combining two strings. You could use "+" to add together integers and doubles. You can concatanate a string with an integer through "+".

String a = "test ";
String b = "this";

System.out.println(a+b);

test this

Math.round rounds to the nearest int
Math.random gives a random number between two numbers

double a = 3.54;
double b = 3.49;

System.out.println(Math.round(a));
System.out.println(Math.round(b));

4
3

Unit 3

Compound boolean values uses logical operators AND and OR to evaulate an expression as true or false

boolean t = true;
boolean f = false;


if (t) {
    System.out.println("1");
}

if (f) {
    System.out.println("2");
}

if (f && !t) {
    System.out.println("3");
}

if (t && !f) {
    System.out.println("4");
}

if (t || f) {
    System.out.println("5");
}

if (!t || !f) {
    System.out.println("6");
}

if ((t && !f) && (t || f)) {
    System.out.println("7");
}

if ((!t || (t && f)) || t ) {
    System.out.println("8");
}

if (!((f || !t) || (f && t))) {
    System.out.println("9");
}

if (!((f && !t) || (f || t))) {
    System.out.println("10");
}

Truth Tables used to see the values of boolean expressions

De Morgan's Law is in essence, Not (A and B) is the same as Not A or Not B
Remember that "!" denotes Not.

boolean test1 = true;
boolean test2 = true;

if (!(test1 && test2)){
    System.out.println("Test1 and Test2 are both false");
}
else{
    System.out.println("They are both true");
}

They are both true

boolean test1 = true;
boolean test2 = true;

if (!test1 || !test2){
    System.out.println("Test1 and Test2 are both false");
}
else{
    System.out.println("They are both true once again");
}

They are both true once again

Unit 4

For loops defines a variable that changes every loop and runs when the conditional is true
Enhanced for loop interates through the whole thing
in the format for (int i : arr)

While loops run when conditional is true
Do While loop runs once no matter what and then checks conditionals

int i=1;   
 
do{    
    System.out.println(i);    
i++;    
}while(i<=10);

int i=11;   
 
do{    
    System.out.println(i);    
i++;    
}while(i<=10);

11

nested loops are loops used inside each other
this can be seen in our monkey nursery rhyme thing

Unit 5

Classes have properties and methods
Properties store information about each object
private and public
Methods runs code
Getter and setter methods are coded to modify private attributes

Classes are created using the class keyword and the first letter is capitalized
main method class is the tester. Automatically called

public class Person {
    
    // automatic unique identifier for Person record
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;

    // email, password, roles are key attributes to login and authentication
    @NotEmpty
    @Size(min=5)
    @Column(unique=true)
    @Email
    private String email;

    @NotEmpty
    private String password;

    // @NonNull, etc placed in params of constructor: "@NonNull @Size(min = 2, max = 30, message = "Name (2 to 30 chars)") String name"
    @NonNull
    @Size(min = 2, max = 30, message = "Name (2 to 30 chars)")
    private String name;

    @DateTimeFormat(pattern = "yyyy-MM-dd")
    private Date dob;
    
    // inches
    public Integer height;

    public Integer weight;

    /* HashMap is used to store JSON for daily "stats"
    "stats": {
        "2022-11-13": {
            "calories": 2200,
            "steps": 8000
        }
    }
    */
    @Type(type="json")
    @Column(columnDefinition = "jsonb")
    private Map<String,Map<String, Object>> stats = new HashMap<>(); 
    

    // Constructor used when building object from an API
    public Person(String email, String password, String name, Integer height, Integer weight, Date dob) {
        this.email = email;
        this.password = password;
        this.name = name;
        this.dob = dob;
        this.height = height;
        this.weight = weight;
    }

    // A custom getter to return age from dob attribute
    public int getAge() {
        if (this.dob != null) {
            LocalDate birthDay = this.dob.toInstant().atZone(ZoneId.systemDefault()).toLocalDate();
            return Period.between(birthDay, LocalDate.now()).getYears(); }
        return -1;
    }

    // note this is just an example. just doing bmi *10
    public int numberofsteps() {
        int numberofsteps = (int) (weight/Math.pow(height, 2) *703 *10);
        return numberofsteps;
    }

    public String toString() {
        return ( "{ \"email\": "  +this.email+  ", " + "\"password\": "  +this.password+ "\"name\": "  +this.name+ "\"height\": "  +this.height+ "\"weight\": "  +this.weight+ "\"dob\": "  +this.dob+ " }" );
    }

    public static void main(String[] args) throws ParseException {
        Date dob = new SimpleDateFormat("MM-dd-yyyy").parse("01-28-2006");

        //no arg
        Person test = new Person();
        System.out.println(test);

        //arg
        Person test2 = new Person("wutwilliam@gmail.com", "CyberPatriot1!", "William Wu", 71, 180, dob);
        System.out.println(test2);
        System.out.println(test2.numberofsteps());
        System.out.println(test2.toString());
    }

}

getters and setters can both be seen in use in this code
they get and set properties of an object
this keywords gets access to properties of the class
public = accessible anywhere
private = accessible only in its own class
static methods dont need an object. part of the class. only initialized once at the start of the execution

public class Example {

    public static void ex() {
        System.out.println("no object needed");
    }

    public static void main(String[] args){
        ex();
    } 
}

Example.main(null);

no object needed

extends in when a class is inherited from a different class
subclass = class that inherits
superclass = class inherited from

public class Super {
    public void ex() {
        System.out.println("test output");
    }
}

public class Sub extends Super {
    public static void main (String[] args) {
           Sub ex1 = new Sub();
    ex1.ex(); 
    }

    
}

Sub.main(null);

test output

toString() returns value to string. automatically ran. can be overrided
hashCode() returns the hash code of an object
Polymorphism is when you have multiple methjods with the same name but different parameters.
Overloading is when you have multiple methods with the same name but different parameters.
Overriding is when you have a method with the same name and parameters as a method in a superclass but you want to modify the method in the subclass.
Late binding is when you have allow the compiler to determine which method to use at runtime instead of compile time.
Big O notation tells you the number of operations an algorithm will make. Determines efficiancy

Unit 1-5 Vocab

Unit 1

Unit 2

Unit 3

Unit 4

Unit 5