Need advice on Schedule Program

[ddmeightball]

I am writing a program that will allow a user to enter in appointments on a schedule. I am having problems with figuring out how to work out the Calendar objects.

My problem is this. Each appointment needs a start time and ending time and a duration. I am having problems trying to figure out how to check to see if an appointment is already taken.

For example, if someone signs up for an appointment at 1:30pm to 2:30pm. This appointment will have a 60 minute duration. Then someone enters an appointment that starts at 1:45pm.

The two starting times are different as we can plainly see so I cant check to see if appointment times are equal, because they arent. I want to be able to check to see if a starting time of an appointment doesnt conflict with another appointments timeslot. Something like if an appointment start time is somewhere in between another appointments start/end time, dont add it.

I was hoping to get some suggestions or even some code examples of what everyone has done to try to solve this problem. Any help is appreciated.

[ddmeightball]

For a further example, here is one.

Here's a pseudocode example:

If startTime <= thisTime <= endTime, there is a conflict.

[System_Error]

Subtract the two dates (the ending time from the starting time) That would be a long value. Get the milliseconds from that. Covert the second controversial time to milliseconds. Compare those. If the second variable is larger than the first then it is a legal uninterrupted appointment. Hope that makes since.

[System_Error]

You could also use compare and see if the third date is greater than the second ending time... Probably a much easier route.

[ddmeightball]

You could also use compare and see if the third date is greater than the second ending time... Probably a much easier route.

System_Error, can you show me an example of using compare(). Are you meaning to compare the date objects or comparing the time attribute of one time object to another?

[ddmeightball]

Allright, here is what I have so far in my timeslot class. I am getting an Null Pointer excpetion on line 16 of my Test.java class when I try to set the begintime of a timeslot object. My code is in the post, it is also available in a zip file.

ts1.setBeginTime(9,15);

Timeslot CLass

import java.util.*;

public class Timeslot {
	private Calendar day;
	private Calendar beginDate;
	private Calendar endDate;
	private Calendar beginTime;
	private Calendar endTime;
	
	private double duration = 1;
	
	public Timeslot() 
	{

	}
	
	public Calendar getBeginDate() 
	{
		return beginDate;
	}
	public void setBeginDate(Calendar bDate) 
	{
		this.beginDate = bDate;
	}
	public void setBeginDate(int year,int month,int date) 
	{
		this.beginDate.set(year, month, date);
	}

	public Calendar getEndDate() 
	{
		return endDate;
	}
	public void setEndDate(Calendar eDate) 
	{
		this.endDate = eDate;
	}
	public void setEndDate(int year,int month,int date) 
	{
		this.endDate.set(year, month, date);
	}

	public Calendar getBeginTime()
	{
		return beginTime;
	}
	public void setBeginTime(Calendar bTime) 
	{
		this.beginTime = bTime;
	}
	public void setBeginTime(int hour, int minute)
	{
		this.beginTime.set(1,1,1,hour, minute);
	}

	public Calendar getEndTime() 
	{
		return endTime;
	}
	public void setEndTime(Calendar eTime) 
	{
		this.endTime = eTime;
	}
	public void setEndTime(int hour, int minute)
	{
		this.endTime.set(1,1,1,hour, minute);
	}
	
	public Calendar getDay() 
	{
		return day;
	}
	public void setDay(Calendar dow)
	{
		this.day = dow;
	}
	
	public boolean compare(Timeslot tsCompare)
	{
		if((this.getBeginTime().getTimeInMillis() >= tsCompare.getBeginTime().getTimeInMillis() || this.getEndTime().getTimeInMillis()<= tsCompare.getBeginTime().getTimeInMillis()))
		{
			return true;
		}
		else
		{
			return false;
		}
	}	
}

Test Class

public class Test {
 Timeslot ts1 = new Timeslot();
 Timeslot ts2 = new Timeslot();

	public static void main(String[] args) {
		new Test();
	}

	public Test() {
		ts1.setBeginTime(9,15);
		ts1.setEndTime(9,30);
		
		ts2.setBeginTime(15,15);
		ts2.setEndTime(15,30);
		
		if(ts1.compare(ts2))
		{
			System.out.println("Compare returned True");
		}
		else if(!ts1.compare(ts2))
		{
			System.out.println("Compare returned False");
		}
	}	
}

Here is the error message in its entirety if you want to see it.

Exception in thread "main" java.lang.NullPointerException
at Timeslot.setBeginTime(Timeslot.java:53)
at Test.<init>(Test.java:16)
at Test.main(Test.java:7)
Press any key to continue...

Thanks for helping.

[ddmeightball]

I figured out the null pont exception. beginTime is declared as a Calendar object, but it is never set to an instance of the Calendar class. In the setBeginTime method, I am are trying to call the set method on the object, but it hasn't been instantiated yet

Thanks for pointing that out. But my question is how can I instantiate a class that is abstract? I cant do

Calendar cal = new Calendar();

because calendar is abstract.



I could just do something like this:

private Calendar beginDate = Calendar.getInstance();

then set it to something else later in the program.


It would probably be better if I do something like:

Calendar cal = new GregorianCalendar();

since I can instantiate a GregorianCalendar class. I thinking I should create a new java class that extends GregorianCalendar.

[ComputerJy]

I don't think you need beginDate and beginTime in your slot
The calendar object can hold both date and time