1. Exam 2 EXAM 2 Thursday!!! 25% of Final Grade
Everything through Last Week, Lab 9
Know:
loops, switch/case
Files
Input failure (e.g. scan.hasNextInt())
Arrays (declaration, access)

2. Files Review For output to a file: For input from file:
FileOutputStream variable initialized to filename (String) and append (boolean)
PrintWriter variable initialized to FileOutputStream variable
For input from file:
File variable initialized to filename (String)
Scanner variable initialized to File variable

3. mydata.txt file 5 8 9.3 Jon 6 14.335 Bill 0 35.67e9 Mary
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 < loops; i++)
integer = scan.nextInt();
decimal = scan.nextFloat();
name= scan.next();
System.out.print(integer + " ");
System.out.print(decimal + " ");
System.out.print(name + " ");
System.out.println(); }
mydata.txt file 5
8 9.3 Jon
Bill
e9 Mary
Smith
-3 -4e3 xyz
Output:
8 9.3 Jon
Bill
E10 Mary
Smith
-3 – xyz

4. Methods public static void main(String [] args) public static void {…
displayVals();
return(0); }
public static void
displayVals() {
System.out.println(…);
return; /*back to where
we left off */ }

5. Methods
Method: A Discrete Piece of Code that Performs a Specific Operation or Task
Named with a Descriptive Identifier
Called from main() or Another Method
When Called, Program Control (Execution) Is Transferred to the method
Method Performs Required Tasks, and then Possibly Returns a Value
After Return from Method, Control Returns to the Statement Following the Method Call

6. Method Attributes Method Name: Identifier Used to Call method
Method Parameter(s) or Argument(s): Value(s) Passed into method for Use by method Code
Method Return Value: Value Returned by method Back to Calling method

7. Method Parameters (Arguments)
May Pass as Many Parameters as Necessary to method
A Copy of the Value of the Parameter Is Passed to the Method
Changing the Value of the Parameter in the Method Does Not Affect the Value of the Original Variable
This Is Called Pass-by-Value

8. Methods – Return Values
Methods Are Typed According to Their Return Values: void, int, double, etc.
Method Returns a Value to Calling method via return Statement

9. class BasicMethod {
public static void main(String [ ] args)
int val = 9;
System.out.println(“squareVal returned: " + squareVal(val)); }
public static int squareVal(int numToSq)
System.out.println("In squareVal ");
return(numToSq * numToSq);

10. Classes A Class Is an Object Type
A Class Represents a “Thing” (e.g., employee, wrench, list, store, shopping cart, etc.)
Service Class – Class used by Other Programs
Programmers Define Classes with Data Members (or Fields) and Methods
Must Be Created in ClassName.java File

11. Object Declaration class useObject {
public static void main(String [ ] args)
Object varName = new Object();//instance
varName.objectMethod(); //invoke method }}
Instance of Object Type Is Called Invoking Object of Class Methods
varName is an instance of Object
varName is invoking object of objectMethod()

12. Designing a Class Decide How It Will Be Used
Decide on Interface (i.e., public representation, public methods)
Decide on Implementation (i.e., private data and data manipulation)
Example: String Methods (interface) includes length(), toUpper(), toLower(), charAt(), etc.
Example: String Implementation includes (*probably*) char variables to hold characters, integer to hold length (we don’t actually need to know)

13. Constructor Class Method of Same Name
Example: class Employee Method Employee()
Called When Variable Declared (instantiated) of Class Type
Initializes Instantiated Object
May Have Multiple Constructors Each with Different Parameters

14. Access Modifiers Used to Identify What May Use Methods
public – any method may use
private – only methods in same class may use
protected – only methods in same class or related classes may use.

15. Example: Class Employee
Employee emp1;
String firstName;
String lastName;
double salary;
First and last names and salaries are attributes.

16. //Employee.java file
public class Employee {
private String firstName;
private String lastName;
private double salary;
private final double MAXSALARY = ;
public Employee()
firstName = "NoFirstName";
lastName = "NoLastName";
salary = 0.0; }

17. Employee Declaration Employee emp1 = new Employee(); String firstName;
"NoFirstName"
String lastName;
"NoLasttName"
double salary;
0.0

18. Accessor Methods
Public Methods for Getting Attributes of Class

19. public String GetFirstName() return firstName;
class Employee {
private String firstName;
private String lastName;
private double salary;
private final double MAXSALARY = ;
public Employee()
firstName = "NoFirstName";
lastName = "NoLastName";
salary = 0.0; }
public String GetFirstName()
return firstName;
public String GetLastName()
return lastName;
public double GetSalary()
return salary;

20. Client Program A Program that Uses a Class Is a Client of that Class
Class Objects are Declared and Instantiated Using the new keyword.
new ClassName(parameters) Calls Constructor for Class
Class Public Methods Called Using Dot (e.g., variable.GetName();)

21. class useEmployee {
public static void main(String [ ] args)
Employee emp1 = new Employee();
System.out.println("Name is" + emp1.GetFirstName() + " " + emp1.GetLastName()); }

22. Mutator Methods
Class Methods Used to Modify a Class Object are Called Mutator Methods
Allows Restricted Manipulation of Class Object Data

23. public boolean SetSalary(double passedSalary){
if (passedsalary <= MAXSALARY)
salary = passedSalary;
return true; }
else
return false;

24. class useEmployee { public static void main(String [ ] args)
Employee emp1 = new Employee();
System.out.println("Name is" + emp1.GetFirstName() + " " + emp1.GetLastName());
if (emp1.SetSalary(55000))
System.out.println("Salary set to 55000"); }
else
System.out.println("Salary not set");

25. Exam 2 EXAM 2 Thursday!!! 25% of Final Grade
Everything through Last Week, Lab 9
Know:
loops, switch/case
Files
Input failure (e.g. scan.hasNextInt())
Arrays (declaration, access)