Wednesday, January 17, 2007

Lecture 4

Employee Database

  • say you are implementing an employee database
  • Employee' will be an object
  • Employees start out w/ an employee number which is given but never changes
  • default salary is $40,000 which can change or start different
  • employees have names which are initially given but CAN change

  • Need to be able to read:
  • Name
  • Employee Number
  • Annual Salary
  • Monthly Salary

  • these are the 'accessors' for the program.

public class Employee {

public Employee (String name, int enum, double salary)
public Employee (String name, int enum)
//methods: accessors
public String GetName()
public int GetEmNum()
public double GetAnnSalary()
public double GetMonSalary()
//methods: mutators
public void SetName(String Name)
public void SetSalary(double salary)
private String EmployeeName;
private int EmployeeNumber;
private double EmployeeSalary;

  • after writing this on the board Andrew carried on w/ code he prepared before class

Utility Classes And The 'Static' Keyword

  • a utility class is a special class w/ no fields that only provides methods that are useful to other objects.
  • example: java.lang.math

Why Have Utilities?
  1. to organize useful methods in a matter similar to objects
  2. use methods w/o involking storage

double x;

  • the keyword 'static' is used to refer to methods that can be used independantly of objects

class myClass {
public static void mymethod(){}

myClass mc = new myClass();
//legal to say
//also legal to say
myclass.mymethod(); //better practice
//legal to use even if no objects of type myClass exist

ample 2

public class myutil{

public static int addint(int a, int b){

return a+b;



c= myutil.addint(3,4;



return: 7

  • Can prevent the compiler from crashing an object relating to a utility class
    • use a private constructor

private myutil(){}

// prevents someone trying to make a 'myutil' object

  • now no outside class has the right to execute the constructor, so an object type util cannot be created.

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