Casting, specifically for Division

integer and integer resulting in integer
if you want it to become a decimal, make it into a double
type promotion (with an integer and a double value) makes it more complicated, resulting in the decimal

//example
public class Variables {
    public static void main (String[] args) {    

    }
}
System.out.println(10.0/15);

0.6666666666666666

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

int x=10;
int y=15;
System.out.println(1 / 3);
System.out.println(1.0 / 3);
System.out.println(1 / 3.0);
System.out.println((double) x / y);
//type promote; produces decimal answer

0
0.3333333333333333
0.3333333333333333
0.6666666666666666

//modulus
public class Variables
{
   public static void main(String[] args)
   {
   }}

System.out.println(15%10);

5

Casting, specifically for Truncating or Rounding

truncation vs. rounding
Rounding a number in the range [2.5, 3.5) returns the number 3
Truncating a number in the range [3.0, 4.0) returns the number 3
- Where a square bracket '[' denotes inclusion in the range, and a parenthesis '(' denotes non-inclusion in the range -- ie. [3.0, 4.0) is the range of all numbers between 3 and 4, including 3 but not including 4.
truncation; chops off decimal portion

//truncation
public class truncation
{
   public static void main(String[] args)
{}}
//example
int a, b, c;
double d, e;

//declare variables
a = 5;
b = -13;
d = 2.8;

c = a + (int)d; //typecasting
//truncation, cut off decimal
//d became 2 instead of 2.8, so 2 + 5 = 7

System.out.println("c is: " + c);

c is: 7

//rounding
public class rounding
{
   public static void main(String[] args)
{}}

double number = 2.8;
System.out.println( "before rounding: " + number ); 

number = Math.round(number);
System.out.println( "after rounding: " + number ); 

double number = 2.4;
System.out.println( "before rounding: " + number ); 

number = Math.round(number);
System.out.println( "after rounding: " + number );

before rounding: 2.8
after rounding: 3.0
before rounding: 2.4
after rounding: 2.0

Concatenation

appendage of strings

//ex
String firstName = "John ";
String lastName = "Doe";
System.out.println(firstName.concat(lastName));

John Doe

class concatenation
{
    public static void main(String arg[])
    {
        }
}

String str1 = "hello", str2 = " to you", str3 = " too";
str1 = str1 + str2 + str3; // LINE A
System.out.println(str1);
//line a is '+' operator

str2 = str2.concat(str3);
System.out.println(str2); //line B
//concat() method

boolean folklore = true;
boolean evermore = false;
System.out.println("Folklore is a great album." + "\nThis statement is " + folklore); // LINE C
System.out.println("Folklore is a bad album." + "\nThis statement is " + evermore);
//concatenation of a boolean to a string

hello to you too
 to you too
Folklore is a great album.
This statement is true
Folklore is a bad album.
This statement is false

Math Classes (Random Usage)

methods to perform math tasks on numbers
random() returns a random number between 0 (inclusive) and 1
public static double random^

import java.lang.Math;
 
//java.lang.Math.random()
class random {
 
    // driver code
    public static void main(String args[])
    {
    }
}
double rand = Math.random();
System.out.println("Random Number:" + rand);

Random Number:0.7941694146696837

Type Casting in Java

when you assign a value of one primitive data type to another type.

two types of casting in Java:

       - Widening Casting (automatically) - converting a smaller type to a larger type size
             byte -> short -> char -> int -> long -> float -> double

       - Narrowing Casting (manually) - converting a larger type to a smaller size type
             double -> float -> long -> int -> char -> short -> byte

Why wrap int, double, etc?
way to use primitive data types as objects

primitive type and corresponding wrapper class
Wrapper classes are used to convert any data type into an object. The primitive data types are not objects; they do not belong to any class; they are defined in the language itself. Sometimes, it is required to convert data types into objects in Java language.

HOMEWORK

//HW
//2006 FRQ

//2a
public double purchasePrice() {
    return getListPrice() * (1+taxRate);
}
//3a
public int compareCustomer(Customer other)
  {
    int compare =  getName().compareTo(other.getName());
    if (compare == 0) {
      return getID() - other.getID();
    }
    else {
      return compare;
    }
  }