diff --git a/src/main/java/net/sf/marineapi/ais/util/MMSI.java b/src/main/java/net/sf/marineapi/ais/util/MMSI.java
index bd930473..34268ed5 100644
--- a/src/main/java/net/sf/marineapi/ais/util/MMSI.java
+++ b/src/main/java/net/sf/marineapi/ais/util/MMSI.java
@@ -28,49 +28,43 @@
 public class MMSI {
 
 	private static final long MINVALUE = 0;
-	private static final long MAXVALUE = 999999999;
+    private static final long MAXVALUE = 999999999;
 
-	/**
-	 * Checks whether the MMSI value is correct, i.e. within valid range.
-	 *
-	 * @param value MMSI value to check
-	 * @return true if the value is semantically correct.
-	 */
-	public static boolean isCorrect(long value) {
-		return (MINVALUE <= value) && (value <= MAXVALUE);
-	}
+    private static final String[] REGION_DESCRIPTIONS = {
+        "Ship group, coast station, or group of coast stations",
+        "SAR aircraft",
+        "Europe",
+        "North and Central America and Caribbean",
+        "Asia",
+        "Oceana",
+        "Africa",
+        "South America",
+        "Assigned for regional Use",
+        "Nav aids or craft associated with a parent ship",
+        "Invalid MMSI number"
+    };
 
-	/**
-	 * Returns the origin associated with the MMSI number.
-	 *
-	 * @param value MMSI value to stringify
-	 * @return A String describing the region of the transmitter
-	 */
-	public static String toString(long value) {
-		int firstDigit = (int)(value / 100000000L); 
-		switch (firstDigit) {
-		case 0:
-			return "Ship group, coast station, or group of coast stations";
-		case 1:
-			return "SAR aircraft";
-		case 2:
-			return "Europe";
-		case 3:
-			return "North and Central America and Caribbean";
-		case 4:
-			return "Asia";
-		case 5:
-			return "Oceana";
-		case 6:
-			return "Africa";
-		case 7:
-			return "South America";
-		case 8:
-			return "Assigned for regional Use";
-		case 9:
-			return "Nav aids or craft associated with a parent ship";
-		default:	
-			return "Invalid MMSI number";
-		}
-	}
+    /**
+     * Checks whether the MMSI value is correct, i.e. within valid range.
+     *
+     * @param value MMSI value to check
+     * @return true if the value is semantically correct.
+     */
+    public static boolean isCorrect(long value) {
+        return (MINVALUE <= value) && (value <= MAXVALUE);
+    }
+
+    /**
+     * Returns the origin associated with the MMSI number.
+     *
+     * @param value MMSI value to stringify
+     * @return A String describing the region of the transmitter
+     */
+    public static String toString(long value) {
+        int firstDigit = (int) (value / 100000000L);
+        if (0 <= firstDigit && firstDigit <= 9) {
+            return REGION_DESCRIPTIONS[firstDigit];
+        }
+        return REGION_DESCRIPTIONS[10];
+    }
 }
\ No newline at end of file
diff --git a/src/main/java/net/sf/marineapi/ais/util/NavAidType.java b/src/main/java/net/sf/marineapi/ais/util/NavAidType.java
index d55cdc17..4ce06832 100644
--- a/src/main/java/net/sf/marineapi/ais/util/NavAidType.java
+++ b/src/main/java/net/sf/marineapi/ais/util/NavAidType.java
@@ -33,74 +33,52 @@ public class NavAidType {
 	 * @param deviceType Device type value to Stringify.
 	 * @return a text string describing the Nav Aid type
 	 */
-	static public String toString (int deviceType) {
-		switch (deviceType) {
-			case 0:
-				return "Default, Type of Aid to Navigation not specified";
-			case 1:
-				return "Reference point";
-			case 2:
-				return "RACON (radar transponder marking a navigation hazard)";
-			case 3:
-				return "Fixed structure off shore, such as oil platforms, wind farms, rigs";
-			case 4:
-				return "Spare, Reserved for future use";
-			case 5:
-				return "Light, without sectors";
-			case 6:
-				return "Light, with sectors";
-			case 7:
-				return "Leading Light Front";
-			case 8:
-				return "Leading Light Rear";
-			case 9:
-				return "Beacon, Cardinal N";
-			case 10:
-				return "Beacon, Cardinal E";
-			case 11:
-				return "Beacon, Cardinal S";
-			case 12:
-				return "Beacon, Cardinal W";
-			case 13:
-				return "Beacon, Port hand";
-			case 14:
-				return "Beacon, Starboard hand";
-			case 15:
-				return "Beacon, Preferred Channel port hand";
-			case 16:
-				return "Beacon, Preferred Channel starboard hand";
-			case 17:
-				return "Beacon, Isolated danger";
-			case 18:
-				return "Beacon, Safe water";
-			case 19:
-				return "Beacon, Special mark";
-			case 20:
-				return "Cardinal Mark N";
-			case 21:
-				return "Cardinal Mark E";
-			case 22:
-				return "Cardinal Mark S";
-			case 23:
-				return "Cardinal Mark W";
-			case 24:
-				return "Port hand Mark";
-			case 25:
-				return "Starboard hand Mark";
-			case 26:
-				return "Preferred Channel Port hand";
-			case 27:
-				return "Preferred Channel Starboard hand";
-			case 28:
-				return "Isolated danger";
-			case 29:
-				return "Safe Water";
-			case 30:
-				return "Special Mark";
-			case 31:
-				return "Light Vessel / LANBY / Rigs";
-			default:
-				return "not used";
-		}
-	}
+	static private String[] navAidTypes = {
+	        "Default, Type of Aid to Navigation not specified",
+	        "Reference point",
+	        "RACON (radar transponder marking a navigation hazard)",
+	        "Fixed structure off shore, such as oil platforms, wind farms, rigs",
+	        "Spare, Reserved for future use",
+	        "Light, without sectors",
+	        "Light, with sectors",
+	        "Leading Light Front",
+	        "Leading Light Rear",
+	        "Beacon, Cardinal N",
+	        "Beacon, Cardinal E",
+	        "Beacon, Cardinal S",
+	        "Beacon, Cardinal W",
+	        "Beacon, Port hand",
+	        "Beacon, Starboard hand",
+	        "Beacon, Preferred Channel port hand",
+	        "Beacon, Preferred Channel starboard hand",
+	        "Beacon, Isolated danger",
+	        "Beacon, Safe water",
+	        "Beacon, Special mark",
+	        "Cardinal Mark N",
+	        "Cardinal Mark E",
+	        "Cardinal Mark S",
+	        "Cardinal Mark W",
+	        "Port hand Mark",
+	        "Starboard hand Mark",
+	        "Preferred Channel Port hand",
+	        "Preferred Channel Starboard hand",
+	        "Isolated danger",
+	        "Safe Water",
+	        "Special Mark",
+	        "Light Vessel / LANBY / Rigs",
+	        "not used"
+	    };
+
+	    /**
+	     * Returns a text string for the NavAid.
+	     *
+	     * @param deviceType Device type value to Stringify.
+	     * @return a text string describing the Nav Aid type
+	     */
+	    static public String toString(int deviceType) {
+	        if (deviceType >= 0 && deviceType < navAidTypes.length) {
+	            return navAidTypes[deviceType];
+	        }
+	        return "not used";
+	    }
 }
diff --git a/src/main/java/net/sf/marineapi/ais/util/PositioningDevice.java b/src/main/java/net/sf/marineapi/ais/util/PositioningDevice.java
index 61a060d3..a88f4259 100644
--- a/src/main/java/net/sf/marineapi/ais/util/PositioningDevice.java
+++ b/src/main/java/net/sf/marineapi/ais/util/PositioningDevice.java
@@ -21,42 +21,67 @@
 package net.sf.marineapi.ais.util;
 
 /**
- * Checks the positioning device type for validity.
+ * Provides functionality related to positioning devices.
  * 
  * @author Lázár József
  */
 public class PositioningDevice {
-	
-	/**
-	 * Returns a text string for the EPFD.
-	 *
-	 * @param deviceType Device type value to Stringify.
-	 * @return a text string describing the positioning device type
-	 */
-	static public String toString (int deviceType) {
-		switch (deviceType) {
-		case 0:
-			return "undefined device";
-		case 1:
-			return "GPS";
-		case 2:
-			return "GLONASS";
-		case 3:
-			return "combined GPS/GLONASS";
-		case 4:
-			return "Loran-C";
-		case 5:
-			return "Chayka";
-		case 6:
-			return "integrated navigation system";
-		case 7:
-			return "surveyed";
-		case 8:
-			return "Galileo";
-		case 15:
-			return "internal GNSS";
-		default:
-			return "not used";
-		}
-	}
+
+    private static final String[] DEVICE_TYPES = {
+        "undefined device",
+        "GPS",
+        "GLONASS",
+        "combined GPS/GLONASS",
+        "Loran-C",
+        "Chayka",
+        "integrated navigation system",
+        "surveyed",
+        "Galileo",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "internal GNSS",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used",
+        "not used"
+    };
+
+    /**
+     * Returns a text string for the EPFD.
+     *
+     * @param deviceType Device type value to stringify.
+     * @return a text string describing the positioning device type
+     */
+    static public String toString(int deviceType) {
+        if (isValidDeviceType(deviceType)) {
+            return DEVICE_TYPES[deviceType];
+        }
+        return "not used";
+    }
+
+    /**
+     * Checks whether the device type value is correct.
+     *
+     * @param deviceType Device type value to check.
+     * @return true if the value is semantically correct.
+     */
+    static private boolean isValidDeviceType(int deviceType) {
+        return 0 <= deviceType && deviceType < DEVICE_TYPES.length;
+    }
 }
diff --git a/src/main/java/net/sf/marineapi/ais/util/ShipType.java b/src/main/java/net/sf/marineapi/ais/util/ShipType.java
index f7f04a2f..7ba66d46 100644
--- a/src/main/java/net/sf/marineapi/ais/util/ShipType.java
+++ b/src/main/java/net/sf/marineapi/ais/util/ShipType.java
@@ -1,182 +1,134 @@
-/*
- * ShipType.java
- * Copyright (C) 2015-2020 Lázár József, Joshua Sweaney
- *
- * This file is part of Java Marine API.
- * <http://ktuukkan.github.io/marine-api/>
- *
- * Java Marine API is free software: you can redistribute it and/or modify it
- * under the terms of the GNU Lesser General Public License as published by the
- * Free Software Foundation, either version 3 of the License, or (at your
- * option) any later version.
- *
- * Java Marine API is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
- * for more details.
- *
- * You should have received a copy of the GNU Lesser General Public License
- * along with Java Marine API. If not, see <http://www.gnu.org/licenses/>.
- */
-package net.sf.marineapi.ais.util;
-
-/**
- * Checks the ship type for validity.
- * 
- * @author Lázár József, Joshua Sweaney
- */
 public class ShipType {
 
-	final static private String[] SPECIAL = {
-			"Pilot vessel",
-			"Search and rescue vessel",
-			"Tug",
-			"Port tender",
-			"Vessel with anti-pollution capability",
-			"Law enforcement vessel",
-			"Spare - for local vessels",
-			"Spare - for local vessels",
-			"Medical transport",
-			"Ship not party to an armed conflict"
-	};
+    private static final String[] SPECIAL = {
+            "Pilot vessel",
+            "Search and rescue vessel",
+            "Tug",
+            "Port tender",
+            "Vessel with anti-pollution capability",
+            "Law enforcement vessel",
+            "Spare - for local vessels",
+            "Spare - for local vessels",
+            "Medical transport",
+            "Ship not party to an armed conflict"
+    };
+
+    private static final String[] FIRST_DIGIT = {
+            "Not specified",
+            "Reserved for future use",
+            "WIG",
+            "Vessel",
+            "HSC",
+            "See above",
+            "Passenger ship",
+            "Cargo ship",
+            "Tanker",
+            "Other types of ship"
+    };
+
+    private static final String[] SECOND_DIGIT = {
+            "General",
+            "Category X",
+            "Category Y",
+            "Category Z",
+            "Category OS",
+            "Reserved for future use",
+            "Reserved for future use",
+            "Reserved for future use",
+            "Reserved for future use",
+            "No additional information"
+    };
+
+    private static final String[] VESSEL = {
+            "Fishing",
+            "Towing",
+            "Towing and exceeding",
+            "Engaged in dredging or underwater operations",
+            "Engaged in diving operations",
+            "Engaged in military operations",
+            "Sailing",
+            "Pleasure craft",
+            "Reserved for future use",
+            "Reserved for future use"
+    };
 
-	final static private String[] FIRST_DIGIT = {
-			"Not specified",
-			"Reserved for future use",
-			"WIG",
-			"Vessel",
-			"HSC",
-			"See above",
-			"Passenger ship",
-			"Cargo ship",
-			"Tanker",
-			"Other types of ship"
-	};
-	
-	final static private String[] SECOND_DIGIT = {
-			"General",
-			"Category X",
-			"Category Y",
-			"Category Z",
-			"Category OS",
-			"Reserved for future use",
-			"Reserved for future use",
-			"Reserved for future use",
-			"Reserved for future use",
-			"No additional information"
-	};
+    /**
+     * Return string describing the ship and cargo type.
+     *
+     * @param type Ship and cargo type indicator
+     * @return a text string describing the ship and cargo type.
+     */
+    public static String shipTypeToString(int type) {
+        if (isValidType(type)) {
+            int d1 = type / 10;
+            int d2 = type % 10;
 
-	final static private String[] VESSEL = {
-			"Fishing",
-			"Towing",
-			"Towing and exceeding",
-			"Engaged in dredging or underwater operations",
-			"Engaged in diving operations",
-			"Engaged in military operations",
-			"Sailing",
-			"Pleasure craft",
-			"Reserved for future use",
-			"Reserved for future use"
-	};
-	
-	/**
-	 * Return string describing the ship and cargo type.
-	 *
-	 * @param type Ship and cargo type indicator
-	 * @return a text string describing the ship and cargo type.
-	 */
-	static public String shipTypeToString (int type) {
-		String typeStr ="N/A";
-		if (0 <= type && type <= 255) {
-			if (type >= 200)
-				return "Reserved for future use";
-			if (type >= 100)
-				return "Reserved for regional use";
-			if (type == 0)
-				return "Not available / no ship";
+            switch (d1) {
+                case 0:
+                    return FIRST_DIGIT[0] + " " + Integer.toString(type);
+                case 3:
+                    return FIRST_DIGIT[3] + ", " + VESSEL[d2];
+                case 5:
+                    return SPECIAL[d2];
+                default:
+                    return FIRST_DIGIT[d1] + ", " + SECOND_DIGIT[d2];
+            }
+        }
+        return "N/A";
+    }
 
-			int d1 = type / 10;
-			int d2 = type % 10;
-			if (0 <= d1 && d1 <= 9 && 0 <= d2 && d2 <= 9) {
-				switch(d1) {
-					case 0:
-						return FIRST_DIGIT[0] + " " + Integer.toString(type);
-					case 3:
-						return FIRST_DIGIT[3] + ", " + VESSEL[d2];
-					case 5: 
-						return SPECIAL[d2];
-					default:
-						return FIRST_DIGIT[d1] + ", " + SECOND_DIGIT[d2]; 
-				}
-			}
-		}
-		return typeStr;
-	}
+    /**
+     * Returns a string describing the first digit. Describes the type of vessel.
+     *
+     * @param type Ship and cargo type indicator
+     * @return String a text string describing the ship type digit
+     */
+    public static String shipTypeToVesselString(int type) {
+        if (isValidType(type)) {
+            int d1 = type / 10;
+            int d2 = type % 10;
 
-	/**
-	 * Returns a string describing the first digit. Describes the type of vessel.
-	 * @param type Ship and cargo type indicator
-	 * @return String a text string describing the ship type digit
-	 */
-	static public String shipTypeToVesselString(int type) {
-		String typeStr ="N/A";
-		if (0 <= type && type <= 255) {
-			if (type >= 200)
-				return "Reserved for future use";
-			if (type >= 100)
-				return "Reserved for regional use";
-			if (type == 0)
-				return "Not available / no ship";
+            switch (d1) {
+                case 0:
+                    return FIRST_DIGIT[0] + " " + Integer.toString(type);
+                case 3:
+                    return FIRST_DIGIT[3];
+                case 5:
+                    return SPECIAL[d2];
+                default:
+                    return FIRST_DIGIT[d1];
+            }
+        }
+        return "N/A";
+    }
 
-			int d1 = type / 10;
-			int d2 = type % 10;
-			if (0 <= d1 && d1 <= 9 && 0 <= d2 && d2 <= 9) {
-				switch(d1) {
-					case 0:
-						return FIRST_DIGIT[0] + " " + Integer.toString(type); // Ship type not specified, so just print whole type number
-					case 3:
-						return FIRST_DIGIT[3]; // Vessel
-					case 5: 
-						return SPECIAL[d2]; // Describes special vessel types for vessels in U.S. waters
-					default:
-						return FIRST_DIGIT[d1]; // Ship type
-				}
-			}
-		}
-		return typeStr;		
-	}
+    /**
+     * Returns a string describing the second digit. Usually describes the type of cargo being carried,
+     * but may also describe the activity the vessel is engaged in.
+     *
+     * @param type Ship and cargo type indicator
+     * @return String a text string describing the cargo type digit
+     */
+    public static String shipTypeToCargoString(int type) {
+        if (isValidType(type)) {
+            int d1 = type / 10;
+            int d2 = type % 10;
 
-	/**
-	 * Returns a string describing the second digit. Usually describes the type
-	 * of cargo being carried, but may also describe the activity the vessel is engaged in.
-	 * @param type Ship and cargo type indicator
-	 * @return String a text string describing the cargo type digit
-	 */
-	static public String shipTypeToCargoString(int type) {
-		String typeStr ="N/A";
-		if (0 <= type && type <= 255) {
-			if (type >= 200)
-				return "Reserved for future use";
-			if (type >= 100)
-				return "Reserved for regional use";
-			if (type == 0)
-				return "Not available / no ship";
+            switch (d1) {
+                case 0:
+                    return FIRST_DIGIT[0] + " " + Integer.toString(type);
+                case 3:
+                    return VESSEL[d2];
+                case 5:
+                    return SPECIAL[d2];
+                default:
+                    return SECOND_DIGIT[d2];
+            }
+        }
+        return "N/A";
+    }
 
-			int d1 = type / 10;
-			int d2 = type % 10;
-			if (0 <= d1 && d1 <= 9 && 0 <= d2 && d2 <= 9) {
-				switch(d1) {
-					case 0:
-						return FIRST_DIGIT[0] + " " + Integer.toString(type); // Cargo not specified, so just print whole type number
-					case 3:
-						return VESSEL[d2]; // Describes an activity the vessel is engaged in
-					case 5: 
-						return SPECIAL[d2]; // Describes special vessel types for vessels in U.S. waters
-					default:
-						return SECOND_DIGIT[d2]; // Describes the cargo being carried
-				}
-			}
-		}
-		return typeStr;
-	}
-}
\ No newline at end of file
+    private static boolean isValidType(int type) {
+        return 0 <= type && type <= 255 && type < 100 || (type >= 100 && type < 200) || type >= 200 && type < 256;
+    }
+}
diff --git a/src/main/java/net/sf/marineapi/provider/PositionProvider.java b/src/main/java/net/sf/marineapi/provider/PositionProvider.java
index 9eeb616c..aae67811 100644
--- a/src/main/java/net/sf/marineapi/provider/PositionProvider.java
+++ b/src/main/java/net/sf/marineapi/provider/PositionProvider.java
@@ -1,172 +1,109 @@
-/* 
- * PositionProvider.java
- * Copyright (C) 2011 Kimmo Tuukkanen
- * 
- * This file is part of Java Marine API.
- * <http://ktuukkan.github.io/marine-api/>
- * 
- * Java Marine API is free software: you can redistribute it and/or modify it
- * under the terms of the GNU Lesser General Public License as published by the
- * Free Software Foundation, either version 3 of the License, or (at your
- * option) any later version.
- * 
- * Java Marine API is distributed in the hope that it will be useful, but
- * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
- * for more details.
- * 
- * You should have received a copy of the GNU Lesser General Public License
- * along with Java Marine API. If not, see <http://www.gnu.org/licenses/>.
- */
-package net.sf.marineapi.provider;
+public class PositionProvider extends AbstractProvider<PositionEvent> {
 
-import net.sf.marineapi.nmea.io.SentenceReader;
-import net.sf.marineapi.nmea.parser.DataNotAvailableException;
-import net.sf.marineapi.nmea.sentence.GGASentence;
-import net.sf.marineapi.nmea.sentence.GLLSentence;
-import net.sf.marineapi.nmea.sentence.RMCSentence;
-import net.sf.marineapi.nmea.sentence.VTGSentence;
-import net.sf.marineapi.nmea.sentence.Sentence;
-import net.sf.marineapi.nmea.sentence.SentenceId;
-import net.sf.marineapi.nmea.util.DataStatus;
-import net.sf.marineapi.nmea.util.Date;
-import net.sf.marineapi.nmea.util.FaaMode;
-import net.sf.marineapi.nmea.util.GpsFixQuality;
-import net.sf.marineapi.nmea.util.Position;
-import net.sf.marineapi.nmea.util.Time;
-import net.sf.marineapi.provider.event.PositionEvent;
+    public PositionProvider(SentenceReader reader) {
+        super(reader, SentenceId.RMC, SentenceId.GGA, SentenceId.GLL, SentenceId.VTG);
+    }
 
-/**
- * <p>
- * Provides Time, Position and Velocity reports from GPS. Data is captured from
- * RMC, GGA and GLL sentences. RMC is used for date/time, speed and course. GGA
- * is used as primary source for position as it contains also the altitude. When
- * GGA is not available, position may be taken from GLL or RMC. If this is the
- * case, there is no altitude included in the
- * {@link net.sf.marineapi.nmea.util.Position}. GPS data statuses are also
- * captured and events are dispatched only when sentences report
- * {@link net.sf.marineapi.nmea.util.DataStatus#ACTIVE}. FAA mode transmitted in
- * RMC is also checked and captured when available, but may be {@code null}
- * depending on used NMEA version.
- *  
- * @author Kimmo Tuukkanen
- * @see net.sf.marineapi.provider.event.PositionListener
- * @see net.sf.marineapi.provider.event.PositionEvent
- * @see net.sf.marineapi.nmea.io.SentenceReader
- */
-public class PositionProvider extends AbstractProvider<PositionEvent> {
+    @Override
+    protected PositionEvent createProviderEvent() {
+        Position p = null;
+        Double sog = null;
+        Double cog = null;
+        Date d = null;
+        Time t = null;
+        FaaMode mode = null;
+        GpsFixQuality fix = null;
+
+        for (Sentence s : getSentences()) {
+            if (s instanceof RMCSentence) {
+                handleRMCSentence((RMCSentence) s, p, sog, cog, d, t, mode);
+            } else if (s instanceof VTGSentence) {
+                handleVTGSentence((VTGSentence) s, sog, cog);
+            } else if (s instanceof GGASentence) {
+                handleGGASentence((GGASentence) s, p, d, t, fix);
+            } else if (s instanceof GLLSentence) {
+                handleGLLSentence((GLLSentence) s, p);
+            }
+        }
+
+        if (d == null) {
+            d = new Date();
+        }
 
-	/**
-	 * Creates a new instance of PositionProvider.
-	 * 
-	 * @param reader SentenceReader that provides the required sentences.
-	 */
-	public PositionProvider(SentenceReader reader) {
-		super(reader, SentenceId.RMC, SentenceId.GGA, SentenceId.GLL, SentenceId.VTG);
-	}
+        return new PositionEvent(this, p, sog, cog, d, t, mode, fix);
+    }
 
-	/*
-	 * (non-Javadoc)
-	 * @see net.sf.marineapi.provider.AbstractProvider#createProviderEvent()
-	 */
-	@Override
-	protected PositionEvent createProviderEvent() {
-		Position p = null;
-		Double sog = null;
-		Double cog = null;
-		Date d = null;
-		Time t = null;
-		FaaMode mode = null;
-		GpsFixQuality fix = null;
+    private void handleRMCSentence(RMCSentence rmc, Position p, Double sog, Double cog, Date d, Time t, FaaMode mode) {
+        sog = rmc.getSpeed();
+        try {
+            cog = rmc.getCourse();
+        } catch (DataNotAvailableException e) {
+            // If we are not moving, course can be undefined. Leave null in that case.
+        }
+        d = rmc.getDate();
+        t = rmc.getTime();
+        if (p == null) {
+            p = rmc.getPosition();
+            if (rmc.getFieldCount() > 11) {
+                mode = rmc.getMode();
+            }
+        }
+    }
 
-		for (Sentence s : getSentences()) {
-			if (s instanceof RMCSentence) {
-				RMCSentence rmc = (RMCSentence) s;
-				sog = rmc.getSpeed();
-				try {
-					cog = rmc.getCourse();
-				} catch (DataNotAvailableException e) {
-					// If we are not moving, cource can be undefined. Leave null in that case.
-				}
-				d = rmc.getDate();
-				t = rmc.getTime();
-				if (p == null) {
-					p = rmc.getPosition();
-					if(rmc.getFieldCount() > 11) {
-						mode = rmc.getMode();
-					}
-				}
-			} else if (s instanceof VTGSentence) {
-				VTGSentence vtg = (VTGSentence) s;
-				sog = vtg.getSpeedKnots();
-				try {
-					cog = vtg.getTrueCourse();
-				} catch (DataNotAvailableException e) {
-					// If we are not moving, cource can be undefined. Leave null in that case.
-				}
-			} else if (s instanceof GGASentence) {
-				// Using GGA as primary position source as it contains both
-				// position and altitude
-				GGASentence gga = (GGASentence) s;
-				p = gga.getPosition();
-				fix = gga.getFixQuality();
+    private void handleVTGSentence(VTGSentence vtg, Double sog, Double cog) {
+        sog = vtg.getSpeedKnots();
+        try {
+            cog = vtg.getTrueCourse();
+        } catch (DataNotAvailableException e) {
+            // If we are not moving, course can be undefined. Leave null in that case.
+        }
+    }
 
-				// Some receivers do not provide RMC message
-				if (t == null) {
-					t = gga.getTime();
-				}
-			} else if (s instanceof GLLSentence && p == null) {
-				GLLSentence gll = (GLLSentence) s;
-				p = gll.getPosition();
-			}
-		}
+    private void handleGGASentence(GGASentence gga, Position p, Date d, Time t, GpsFixQuality fix) {
+        p = gga.getPosition();
+        fix = gga.getFixQuality();
 
-		// Ag-Star reciever does not provide RMC sentence. So we have to guess what date it is
-		if (d == null) {
-			d = new Date();
-		}
+        // Some receivers do not provide RMC message
+        if (t == null) {
+            t = gga.getTime();
+        }
+    }
 
-		return new PositionEvent(this, p, sog, cog, d, t, mode, fix);
-	}
+    private void handleGLLSentence(GLLSentence gll, Position p) {
+        p = gll.getPosition();
+    }
 
-	/*
-	 * (non-Javadoc)
-	 * @see net.sf.marineapi.provider.AbstractProvider#isReady()
-	 */
-	@Override
-	protected boolean isReady() {
-		return hasOne("RMC", "VTG") && hasOne("GGA", "GLL");
-	}
+    @Override
+    protected boolean isReady() {
+        return hasOne("RMC", "VTG") && hasOne("GGA", "GLL");
+    }
 
-	/*
-	 * (non-Javadoc)
-	 * @see net.sf.marineapi.provider.AbstractProvider#isValid()
-	 */
-	@Override
-	protected boolean isValid() {
+    @Override
+    protected boolean isValid() {
+        for (Sentence s : getSentences()) {
+            if (s instanceof RMCSentence && !isValidRMCSentence((RMCSentence) s)) {
+                return false;
+            } else if (s instanceof GGASentence && !isValidGGASentence((GGASentence) s)) {
+                return false;
+            } else if (s instanceof GLLSentence && !isValidGLLSentence((GLLSentence) s)) {
+                return false;
+            }
+        }
+        return true;
+    }
 
-		for (Sentence s : getSentences()) {
+    private boolean isValidRMCSentence(RMCSentence rmc) {
+        DataStatus ds = rmc.getStatus();
+        return !DataStatus.VOID.equals(ds) && !(rmc.getFieldCount() > 11 && FaaMode.NONE.equals(rmc.getMode()));
+    }
 
-			if (s instanceof RMCSentence) {
-				RMCSentence rmc = (RMCSentence)s;
-				DataStatus ds = rmc.getStatus();
-				if (DataStatus.VOID.equals(ds) ||
-					(rmc.getFieldCount() > 11 && FaaMode.NONE.equals(rmc.getMode()))) {
-					return false;
-				}
-			} else if (s instanceof GGASentence) {
-				GpsFixQuality fq = ((GGASentence) s).getFixQuality();
-				if (GpsFixQuality.INVALID.equals(fq)) {
-					return false;
-				}
-			} else if (s instanceof GLLSentence) {
-				DataStatus ds = ((GLLSentence) s).getStatus();
-				if (DataStatus.VOID.equals(ds)) {
-					return false;
-				}
-			}
-		}
+    private boolean isValidGGASentence(GGASentence gga) {
+        GpsFixQuality fq = gga.getFixQuality();
+        return !GpsFixQuality.INVALID.equals(fq);
+    }
 
-		return true;
-	}
+    private boolean isValidGLLSentence(GLLSentence gll) {
+        DataStatus ds = gll.getStatus();
+        return !DataStatus.VOID.equals(ds);
+    }
 }
diff --git a/src/test/java/net/sf/marineapi/nmea/parser/GGATest.java b/src/test/java/net/sf/marineapi/nmea/parser/GGATest.java
index dfd8034a..ad15c9e7 100644
--- a/src/test/java/net/sf/marineapi/nmea/parser/GGATest.java
+++ b/src/test/java/net/sf/marineapi/nmea/parser/GGATest.java
@@ -146,10 +146,14 @@ public void testSetAltitude() {
 	}
 
 	@Test
-	public void testSetAltitudeUnits() {
-		assertEquals(Units.METER, gga.getAltitudeUnits());
-		gga.setAltitudeUnits(Units.FEET);
-		assertEquals(Units.FEET, gga.getAltitudeUnits());
+	public void testDefaultAltitudeUnits() {
+	    assertEquals(Units.METER, gga.getAltitudeUnits());
+	}
+
+	@Test
+	public void testSetAltitudeUnitsToFeet() {
+	    gga.setAltitudeUnits(Units.FEET);
+	    assertEquals(Units.FEET, gga.getAltitudeUnits());
 	}
 
 	@Test
@@ -166,10 +170,14 @@ public void testSetDgpsStationId() {
 	}
 
 	@Test
-	public void testSetFixQuality() {
-		assertEquals(GpsFixQuality.NORMAL, gga.getFixQuality());
-		gga.setFixQuality(GpsFixQuality.INVALID);
-		assertEquals(GpsFixQuality.INVALID, gga.getFixQuality());
+	public void testDefaultFixQuality() {
+	    assertEquals(GpsFixQuality.NORMAL, gga.getFixQuality());
+	}
+
+	@Test
+	public void testSetFixQualityToInvalid() {
+	    gga.setFixQuality(GpsFixQuality.INVALID);
+	    assertEquals(GpsFixQuality.INVALID, gga.getFixQuality());
 	}
 
 	@Test
@@ -180,10 +188,14 @@ public void testSetGeoidalHeight() {
 	}
 
 	@Test
-	public void testSetGeoidalHeightUnits() {
-		assertEquals(Units.METER, gga.getGeoidalHeightUnits());
-		gga.setGeoidalHeightUnits(Units.FEET);
-		assertEquals(Units.FEET, gga.getGeoidalHeightUnits());
+	public void testDefaultGeoidalHeightUnits() {
+	    assertEquals(Units.METER, gga.getGeoidalHeightUnits());
+	}
+
+	@Test
+	public void testSetGeoidalHeightUnitsToFeet() {
+	    gga.setGeoidalHeightUnits(Units.FEET);
+	    assertEquals(Units.FEET, gga.getGeoidalHeightUnits());
 	}
 
 	@Test
diff --git a/src/test/java/net/sf/marineapi/nmea/parser/TXTTest.java b/src/test/java/net/sf/marineapi/nmea/parser/TXTTest.java
index e353e570..969b2dc1 100644
--- a/src/test/java/net/sf/marineapi/nmea/parser/TXTTest.java
+++ b/src/test/java/net/sf/marineapi/nmea/parser/TXTTest.java
@@ -32,9 +32,17 @@ public void testStringConstructor() {
     }
 
     @Test
-    public void testTalkerIdConstructor() {
+    public void testTalkerId() {
         assertEquals(TalkerId.II, empty.getTalkerId());
+    }
+
+    @Test
+    public void testSentenceId() {
         assertEquals("TXT", empty.getSentenceId());
+    }
+
+    @Test
+    public void testFieldCount() {
         assertEquals(4, empty.getFieldCount());
     }
 
diff --git a/src/test/java/net/sf/marineapi/nmea/parser/XTETest.java b/src/test/java/net/sf/marineapi/nmea/parser/XTETest.java
index 062b5a77..e12a4be6 100644
--- a/src/test/java/net/sf/marineapi/nmea/parser/XTETest.java
+++ b/src/test/java/net/sf/marineapi/nmea/parser/XTETest.java
@@ -26,19 +26,43 @@ public void setUp() throws Exception {
 	}
 
 	@Test
-	public void testXTEParserString() {
-		assertEquals(TalkerId.II, instance.getTalkerId());
-		assertEquals(SentenceId.XTE.name(), instance.getSentenceId());
-		assertEquals(6, instance.getFieldCount());
-		assertTrue(instance.isValid());
+	public void testTalkerId() {
+	    assertEquals(TalkerId.II, instance.getTalkerId());
 	}
 
 	@Test
-	public void testXTEParserTalkerId() {
-		assertEquals(TalkerId.GP, empty.getTalkerId());
-		assertEquals(SentenceId.XTE.name(), empty.getSentenceId());
-		assertEquals(6, empty.getFieldCount());
-		assertTrue(empty.isValid());
+	public void testSentenceId() {
+	    assertEquals(SentenceId.XTE.name(), instance.getSentenceId());
+	}
+
+	@Test
+	public void testFieldCount() {
+	    assertEquals(6, instance.getFieldCount());
+	}
+
+	@Test
+	public void testIsValid() {
+	    assertTrue(instance.isValid());
+	}
+
+	@Test
+	public void testTalkerId() {
+	    assertEquals(TalkerId.GP, empty.getTalkerId());
+	}
+
+	@Test
+	public void testSentenceId() {
+	    assertEquals(SentenceId.XTE.name(), empty.getSentenceId());
+	}
+
+	@Test
+	public void testFieldCount() {
+	    assertEquals(6, empty.getFieldCount());
+	}
+
+	@Test
+	public void testIsValid() {
+	    assertTrue(empty.isValid());
 	}
 
 	@Test