Scheduled Calendar in Java

Question

Could someone explain where the inputs would come from in this skeleton code.

The skeleton code is as follows:

Data.java

import java.util.Date;
import java.util.List;

public interface Data {

// Return a list of all appointments at the given location (at any time)
// If there are no such appointments, return an empty list
// Throws IllegalArgumentException if the argument is null
public List<Schedule> getSchedule(String location);

// Return the next appointment at or after the given time (in any location)
// If there is no such appointment, return null
// Throws IllegalArgumentException if the argument is null
public Schedule getNextSchedule(Date when);

// Return the next appointment at or after the given time, at that location
// If there is no such appointment, return null
// Throws IllegalArgumentException if any argument is null
public Schedule getNextSchedule(Date when, String location);

// Create a new appointment in the calendar
// Throws IllegalArgumentException if any argument is null
public void add(String description, Date when, String location);

// Remove an appointment from the calendar
// Throws IllegalArgumentException if the argument is null
public void remove(Schedule schedule);
}

Calendar.java

import java.util.Date;
import java.util.List;

public class Calendar implements Data {

// We will use this when we test
public Calendar() {
}

@Override
public List<Schedule> getSchedule(String location) {
    // TODO
    return null;
}

@Override
public Schedule getNextSchedule(Date when) {
    if(when == null) {
        throw new IllegalArgumentException("time was null");
    }
    // TODO
    return null;
}

@Override
public Schedule getNextSchedule(Date when, String location) {
    // TODO
    return null;
}

@Override
public void add(String description, Date when, String location) {
    // TODO
}

@Override
public void remove(Schedule schedule) {
    // TODO
}
}

Schedule.java

import java.util.Date;

public interface Schedule {

public String getDescription();

public String getLocation();

public Date getStartTime();

}

I would also like to know:

• where to start, I attempted to start but I am unsure what to return in the first todo section labeled getSchedule. I know I can't return location because the method calls for a List type(?) to be returned.

Answer 1

The <> are used in Classes like Collections and Maps. means, that there is a Collection (for example an ArrayList) which can contain elements of the type Schedule. If you have a Map like a HashMap then you need to put 2 Types in these <>: The Key (for example Integer) and the Object (for example String)

HashMap<Integer, String>

Now you can get an Element from the Map using

thisIsMyMap.get(7);

This method returns a instance of the Type Schedule whith the key 7, stored in an Integer. You have to use Integer instead of int because a Map or List can't contain the simple Types like int, double, boolean.

Now to your problem: before you can return something in the method getSchedule(String location) you need to have a List to store your Schedules like this:

ArrayList<Schedule> schedules = new ArrayList<Schedule>();

then you can iterate the list in the method getSchedule(String location) and write all entries with the right loation in another list and return it:

@Override
public List<Schedule> getSchedule(String location) {
    ArrayList<Schedule> right = new ArrayList<Schedule>();
    for(int i = 0; i<schedules.size(); i++)
    {
        if(schedules.get(i).getLocation().equals(location))
            right.add(schedules);
    }
    return right;
}

You wrote you wanted to use HashTrees. I think it's better and faster if you just use an ArrayList. Yes, you can put HashTrees in a specific order, but it's much more complicated and it works with Lists too.

Antilog