CSCE 2013L: Lab 2

1
CSCE 2013L Lab 2

• Overview
• Primitive Types in Java
• Notes About Arithmetic Expression Types
• Primitive Type Conversion (Casting)?
• Java Strings
• Input/Output (Command line and Swing)?
• Lab Programs
• NumericTypes.java
• Use proper casting and order of operations to
  correct logic
• Add additional functionality manipulate strings
  and calculate volume
• Mileage.java
• Write a program to calculate miles per gallon
  from scratch

2
Primitive Types in Java

• Primitive in this case means not created from a
  class. These are the most basic types and they
  only hold a single value and have no methods.
• Integer Types
• byte, short, int, long (whole numbers)?
• IEEE Floating Point Types
• float (7 digits), double (15 digits)?
• boolean (true or false)?
• char (a Unicode character)?

3
Arithmetic Expressions

• The result of a division between 2 integers is an
  integer.
• It does not matter if you try to store it in a
  floating point variable. The fractional part will
  be missing.
• Example
• double result 5 / 2
• You might expect result to contain the value 2.5,
  but it actually has 2.0
• Integer division results in truncation

4
Arithmetic Expressions Cont.

• In order for a division to return a floating
  point type, one of the operands must be a float.
  It does not matter which one.
• Example
• double result 5.0 / 2
• double result 5 / 2.0
• Either one of these statements gives the expected
  value of 2.5

5
Primitive Type Conversion(Casting)?

• Java (if it is able to) allows us to convert from
  one type to the other using an operation called
  the cast.
• The name of the type we are converting to goes in
  parentheses in front of the variable name we want
  to convert.
• Examples
• (double)someInteger
• (int)someDouble
• (int)(1.5 1.6) //my value is 3
• (int)1.5 (int)1.6 //my value is 2

6
Java Strings

• The String class is an example of a type Java
  provides that is not primitive.
• We can declare a String variable with
• String myString
• String anotherString Another String
• Strings have various methods that can be called
  such as length() and toUpperCase()?
• We can call a method from an object with the .
  (dot) operator
• int anotherLength anotherString.length()
• The value of anotherLength is 14

7
String Operations

• Strings can be concatenated together with the
  (plus) operator.
• Examples
• String first First
• String last Last
• String firstLast1 first last
• String firstLast2 First Last

8
Useful String Methods

• charAt(index)?
• This method returns the char located at the
  position specified by int index. The numbering
  starts from 0.
• String name Ebony
• char initial name.charAt(0)
• initial now holds the Unicode character for 'E'
• toUpperCase()?
• Returns a new String that is the uppercase
  version of the string contained in the object
• String bigName name.toUpperCase()
• bigName has the value EBONY

9
Output (Command Line)?

• public class Output
• public static void main(String args)?
• System.out.println(Hello, world!)

10
Input (Command Line)?

• import java.util.Scanner
• public class Input
• public static void main(String args)?
• Scanner input new Scanner(System.in)
• String name input.nextLine()

11
Output (Swing)?

• import javax.swing.JOptionPane
• public class OutputSwing
• public static void main(String args)?
• JOptionPane.showMessageDialog(null, Hello,
  world!)

12
Input (Swing)?

• import javax.swing.JOptionPane
• public class InputSwing
• public static void main(String args)?
• String name
• JOptionPane.showInputDialog(What is your
  name?)
• JOptionPane.showMessageDialog(null, Your
  name is name)

13
NumericTypes.java Task Summary

• Task 1
• Correct the errors due to incorrect order of
  operations and improper type conversions
• Task 2
• Use either Scanner or JOptionPane in order to get
  the user's first and last names and output their
  full name.
• Task 3
• Use the methods in String to get the user's
  initial and convert their name to uppercase.
• Task 4
• Write code to calculate the volume of a sphere

14
Mileage.java Task Summary

• Task 5
• Write a program from scratch following the
  guidelines in the lab manual in order to get user
  input to calculate miles per gallon.
• Task 6
• Following the example set by the
  NumericTypes.java, make sure your Mileage.java is
  well-commented. Be sure to provide the exact
  comments that the lab asks for.

15
Command Reference

• How do I compile my program?
• javac MyFile.java
• How do I run my program?
• java MyFile
• How do I submit my assignment?
• submit csce2013-005 elb02 lab2
• if you are enrolled in the Wednesday session
• submit csce2013-004 elb02 lab2
• if you are enrolled in the Monday session
• The files I require for this lab are
  NumericTypes.java, Mileage.java, and the Lab 2
  worksheet