1. Math class services (functions)
Primitive vs reference data types
Scanner class
Suppose you want to find the absolute value of a number.
You could square it and then take the square root. OR
You can ask Math for some help. Math is a class of services
automatically provided to help us with a range of math services.
To request Math’s help in this problem, we essentially say, Math,
calculate the value of this number.
In code, you would see something like this:
double original;
double result;
original = ;
result = Math.abs(original);

2. Appendix G – Math functions
In code, you would see something like this:
double original;
double result;
original = ;
result = Math.abs(original);
Appendix G – Math functions
Lab will include some play with math functions
The argument to the method (value that the method will act upon)
Name of class providing service
Name of the function
(static method)
Math class services (functions)
Primitive vs reference data types
Scanner class
We say that this method, abs, returns a value. In this case that value is assigned to the variable result.
MathPlay.java

3. The object that contains the character string “Charleston”
Reference Types
Primitives
int
byte
long
short
float
double
char
boolean
int num;
num = 5;
When a variable references an object, it contains the memory address of the object’s location.
Then it is said that the variable references the object.
String cityName = "Charleston ";
num 5
The object that contains the
character string “Charleston”
Math class services (functions)
Primitive vs reference data types
Scanner class
cityName
Address to the object
Charleston
Reference types take up 2 chunks of memory, one
that is the named variable that contains an address or
referenceand the other that contains the data contents
of the object.

4. Decimal Formatter – Another class in Java Creating an object
Math class services (functions)
Primitive vs reference data types
Scanner class
Decimal Formatter – Another class in Java
Creating an object
variables
Data type (class name)
DecimalFormat twoDecimals;
DecimalFormat threeDecimals;
twoDecimals = new DecimalFormat(“##0.00”);
threeDecimals = new DecimalFormat(“##0.000”);
We say that we are instantiating a new DecimalFormat
object with the new operation. Below, we use those formats.
Formatting.java
double number1;
number1 = ;
System.out.println(twoDecimals.format(number1);
System.out.println(threeDecimals.format(number1);
Book Chap 3.10

5. 23.4\n567.98\nThis little piggy\n
Math class services (functions)
Primitive vs reference data types
Scanner class
Data type (class name)
variable
Standard input
Scanner keyboard;
keyboard = new Scanner (System.in);
We say that we are instantiating a new Scanner
object with the new operation.
keyboard
23.4\n567.98\nThis little piggy\n
System.in

6. Examples – assume all variables have been initialized to the
Math class services (functions)
Primitive vs reference data types
Scanner class
keyboard
System.in
If I want to read in data, I will use keyboard’s methods to do so, since I want to read from standard input and keyboard references the Scanner object which will read from standard input.
Scanner methods
int: nextInt()
double: nextDouble()
String: next()
String: nextLine()
Examples – assume all variables
have been initialized to the
appropriate types
abc = keyboard.nextInt();
text = keyboard.nextLine();
MPG.java
Book chapter 2.13

7. Scanner methods (except for nextLine()) treat “whitespace”
as a delimiter. For each next method, it will pluck off the next
token.
If the input is not correct, such as using nextInt and the user
has entered “abc”, you will get a runtime error.
If you try to read in a String after you have read in a number,
you must “consume” the new line character prior to reading the String. See page 88 (purple) or 86 (green).
Math class services (functions)
Primitive vs reference data types
Scanner class
InputProblem.java