public void testGetList(){
			try{
			Radar r = new RadarImpl();
			RadarContact r1 = new RadarContactImpl("R1", 15, 1000);
			RadarContact r2 = new RadarContactImpl("R2", 360, 2000);
			RadarContact r3 = new RadarContactImpl("R3", 180, 122.3);
			
			r.addContact(r1);
			r.addContact(r2);
			r.addContact(r3);
			
			List list = r.returnContacts();
			
			assertEquals(list.size(), 3);
			assertTrue(list.contains(r1));
			assertTrue(list.contains(r2));
			assertTrue(list.contains(r3));
			
			list.remove(r1);
			assertEquals(3, r.getContactCount());

public void testRemove(){
			try{
			Radar r = new RadarImpl();
			RadarContact r1 = new RadarContactImpl("R1", 15, 1000);
			RadarContact r2 = new RadarContactImpl("R2", 360, 2000);
			RadarContact r3 = new RadarContactImpl("R3", 180, 122.3);
			
			r.addContact(r1);
			r.addContact(r2);
			r.addContact(r3);
			
			assertEquals(3, r.getContactCount());
			assertNull(r.removeContact("NO_CONTACT"));
			assertSame(r.removeContact("R2"), r2);
			assertNull(r.removeContact(r2.getContactID()));
			assertEquals(2, r.getContactCount());

package sef.module9.activity;

import java.util.Comparator;
import java.util.List;

/**
 * Interface representing the behavior of a Radar 
 *
 */
public interface Radar {

	/**
	 * Adds a RadarContact to the Radar's list of contacts.  Each contact is unique
	 * according to the RadarContact.getContactID().  If another contact is added with the 
	 * same ID, it will replace the attributes of the existing contact with the specified
	 * contact.
	 * 
	 * Null parameters are ignored and not added
	 * 
	 * @param contact the RadarContact to be added
	 * 
	 * @return A reference of the actual RadarContact object added to the contact list
	 */
	public RadarContact addContact(RadarContact contact);
	
	
	/**
	 * Removes the specified contact from the contact list with the specified contactID
	 * This method will return null if the contactID is not listed 
	 * 
	 * @param id the id of the RadarContact to remove
	 * 
	 * @return reference to the RadarContact object removed from the list
	 */
	public RadarContact removeContact(String id);
	
	
	/**
	 * Returns a reference to the RadarContact specified by the parameter.  This
	 * method will return null if the id is not listed
	 * 
	 * @param id the id of the RadarContact to find
	 * 
	 * @return
	 */
	public RadarContact getContact(String id);
	
	
	
	/**
	 * Returns the number of RadarContacts tracked by this Radar
	 * 
	 * @return the count of RadarContacts
	 */
	public int getContactCount();
	
	
	/**
	 * Returns a List of RadarContacts tracked by this Radar.  The order of the list
	 * depends on the current Radar implementation
	 * 
	 * @return List of RadarContacts
	 */
	public List<RadarContact> returnContacts();
	
	
	/**
	 * Returns a list of RadarContacts tracked by this Radar, ordered by the Comparator used
	 * 
	 * @param comparator Comparator to be used
	 * @return ordered List of RadarContacts
	 */
	public List<RadarContact> returnContacts(Comparator<RadarContact> comparator);
	
}

package sef.module9.activity;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

/**
 * Implementation of a Radar 
 * 
 *
 */
public class RadarImpl implements Radar{
	private List<RadarContact>contactList=new ArrayList<>();
	private RadarContact contact;

	
	/**
	 *  Constructs a new Radar 
	 */
	public RadarImpl(){
		
	}
	
	
	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#addContact(sef.module8.activity.RadarContact)
	 */
	public RadarContact addContact(RadarContact contact) {

		removeContact(contact.getContactID());
		contactList.add(contact);

		return contact;
	}


	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#getContact(java.lang.String)
	 */
	public RadarContact getContact(String id) {
		for(RadarContact r:contactList){
			if(r.getContactID().equals(id)){
				return r;
			}
		}
		return null;
	}

	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#getContactCount()
	 */
	public int getContactCount() {
		
		return contactList.size();
	}

	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#removeContact(java.lang.String)
	 */
	public RadarContact removeContact(String id) {
		for(RadarContact r:contactList){
			if(r.getContactID().equals(id)){
				contactList.remove(r);
				return r;

			}
		}return null;

	}

	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#returnContacts()
	 */
	public List<RadarContact> returnContacts() {
		return contactList;
	}

	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#returnContacts(java.util.Comparator)
	 */
	public List<RadarContact> returnContacts(Comparator<RadarContact> comparator) {
		contactList.sort(comparator);
		return contactList;
		//return Collections.sort(arg0, new DistanceComparator());
	}

	
}

Getcontactlist() = return new arraylist(contactlist);

public int getContactCount() {
		
		return ?
	}

public RadarContact removeContact(String id) {
		for(RadarContact r:contactList){
			if(r.getContactID().equals(id)){
				contactList.remove(r);
				return r;

			}
		}return null;

	}

public int getContactCount() {
		
		return new ArrayList<>(contactList).size();
	}

	public List<RadarContact> returnContacts() {
		return new ArrayList<>(contactList);
	}

	/* (non-Javadoc)
	 * @see sef.module8.activity.Radar#returnContacts(java.util.Comparator)
	 */
	public List<RadarContact> returnContacts(Comparator<RadarContact> comparator) {
		contactList.sort(comparator);
		return new ArrayList<>(contactList);
		
	}

List list = r.returnContacts();

public List<RadarContact> returnContacts(Comparator<RadarContact> comparator) {
		contactList.sort(comparator);
		return Collections.unmodifiableList(contactList);
		//return Collections.sort(arg0, new DistanceComparator());
}

List list = r.returnContacts();