Know for Quiz 2

1
Know for Quiz 2

• Everything through Exam 1
• Loops while, for, do-while
• switch-case Statement

2
Strings Revisited

• String Is a Type (Object) in JAVA
• Automatically imported in java.lang
• May Initialize or Assign with Double Quoted
  Values
• Can Add String to String with Operator
• CANNOT Compare using Equality Operators (uses
  .equals() method instead)
• Methods Available to
• Access single characters
• Get length of String
• Find a character or substring in String
• Convert to lower or upper case

3
Objects

• Objects Types of Variables Made from Built-In
  Types
• Variables Can be Declared as an Object Type
• Objects Usually Have Functions Tied to Them
• Member functions
• Public functions
• Interface functions
• Methods
• String Is an Example of an Object Type
• StringVariable.length() Returns the Number of
  Characters in the String

4
Methods

• Also called Procedures, Functions
• Have Parenthesis (e.g., method() )
• May be Passed Arguments, or Parameters
• Parameters are values to initialize new variables
  in method
• Parameters used to pass information to method

5
String Methods

• charAt(int index) return char at named index
  (starting at 0)
• equals(String str) return boolean
• indexOf(char) return int of first occurrence of
  char (index starts at 0)
• indexOf(String substr) return int of first
  occurrence of String substr
• length() return int length of String
• substring(int start, int end) return String
  between start and end
• toLowerCase(), toUpperCase() convert String

6
String myString "My Dog Sandy",compareString
System.out.println("The fourth character is "
myString.charAt(3)) if (myString.equals("my dog
sandy")) System.out.println("Strings are
equal") else System.out.println("Strings are not
equal") compareString myString
myString System.out.println("Added strings are
" compareString) Output The fourth character
is D Strings are not equal Added strings are My
Dog SandyMy Dog Sandy
7

• compareString myString.toLowerCase()
• System.out.println("String is "
  compareString)
• System.out.println("Char S is at location "
  myString.indexOf('S'))
• System.out.println("substring og is at location
  " myString.indexOf("og"))
• System.out.println("Length of string is "
  myString.length())
• System.out.println("substring between location 3
  and 5 is " myString.substring(3,5))
• Output
• String is my dog sandy
• Char S is at location 7
• Substring og is at location 4
• Length of string is 12
• Substring between location 3 and 5 is Do

8

• import java.util.Scanner
• public class MyProgram
• public static void main( String args)
• Scanner scan new Scanner(System.in)
• String lastname
• boolean instructor false
• System.out.print(Enter last name)
• lastname scan.next()
• if(lastname.equals(hanrath))
• instructor true // privileged
• else
• instructor false // not privileged

9
More on Input

• Input Failure Common
• MUST Be Part of Test Plan
• Pages 310-313 in Anderson
• Check Input for Type Desired
• If not, Notify User, and Get Rid of Line

10
Input Failure Example

• import java.util.
• class InputFailureExample
• public static void main(String args)
• int numE
• String garbage
• Scanner scan new Scanner(System.in)
• System.out.print("Enter Integer ")
• while (!scan.hasNextInt())
• garbage scan.nextLine()
• System.out.println("Please try again.")
• System.out.print("Enter Integer ")
• numE scan.nextInt()
• System.out.println("You entered " numE)

11
Files

• Data in Main Memory is volatile
• File Place for permanent data storage
• C drive, A drive, Flash drive, etc.

Main Memory
File
main() int num string firstname
Disk
12
Input Files

• import java.io.
• import java.util.Scanner
• class FileInput
• public static void main(String args) throws
  IOException
• File ifile new File("data.txt")
• Scanner scan new Scanner(ifile)
• while (scan.hasNextInt())
• i scan.nextInt()

13
Output File Streams

• import java.io.
• class FileOutput
• public static void main(String args) throws
  IOException
• int i
• FileOutputStream ofile new FileOutputStream("da
  ta2.txt",false) //trueAPP
• PrintWriter pw new PrintWriter(ofile)
• for (i0i lt 100 i i 2)
• pw.println(i)
• pw.close() // Writes data to file on disk

14

• import java.util.Scanner
• import java.io.
• class FormatFileData
• public static void main(String args) throws
  IOException
• int loops, integer, i
• float decimal
• String name
• File ifile new File("mydata.txt")
• Scanner scan new Scanner(ifile)
• loops scan.nextInt()
• for(i 0 i lt loops i)
• integer scan.nextInt()
• decimal scan.nextFloat()
• name scan.next()

mydata.txt file 5 8 9.3 Jon 6 14.335 Bill 0
35.67e9 Mary -23 -4.55 Smith -3 -4e3 xyz
Output
8 9.3 Jon 6 14.335 Bill 0 3.567E10 Mary -23
-4.55 Smith -3 4000.0 xyz
15
Know for Quiz 2

• Everything through Exam 1
• Loops while, for, do-while
• switch-case Statement