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 {

//constructors
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)
//fields
private String EmployeeName;
private int EmployeeNumber;
private double EmployeeSalary;

Click

• 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

example:
double x;
x.sqrt();

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

example 2


public class myutil{

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

return a+b;

}

}


c= myutil.addint(3,4;

system.out.println(c);

//console

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.