Create QuadString and add simple parser extension to parse NQuad

hdt-api/src/main/java/org/rdfhdt/hdt/exceptions/ParserException.java

@@ -35,6 +35,12 @@ public class ParserException extends Exception {
 
 	private static final long serialVersionUID = -5159336711525269027L;
 
+	private static String createMessage(String message, String line, int location) {
+		int start = Math.max(0, location - 10);
+		int end = Math.min(line.length(), location + 10);
+		return message + " near " + line.substring(start, end);
+	}
+
 	public ParserException() {
 		super();
 	}
@@ -43,6 +49,10 @@ public ParserException(String message) {
 		super(message);
 	}
 
+	public ParserException(String message, String line, int location) {
+		this(createMessage(message, line, location));
+	}
+
 	public ParserException(Throwable e) {
 		super(e);
 	}

hdt-api/src/main/java/org/rdfhdt/hdt/quad/QuadString.java

@@ -0,0 +1,119 @@
+package org.rdfhdt.hdt.quad;
+
+import org.rdfhdt.hdt.exceptions.ParserException;
+import org.rdfhdt.hdt.triples.TripleString;
+
+public class QuadString extends TripleString {
+	protected CharSequence context;
+
+	public QuadString() {
+		super();
+		context = "";
+	}
+
+	public QuadString(CharSequence subject, CharSequence predicate, CharSequence object, CharSequence context) {
+		super(subject, predicate, object);
+		this.context = context;
+	}
+
+	public QuadString(TripleString other) {
+		super(other);
+		this.context = other.getObject();
+	}
+
+	@Override
+	public void clear() {
+		super.clear();
+		context = "";
+	}
+
+	@Override
+	public boolean equals(Object other) {
+		if (context.length() == 0) {
+			return super.equals(other);
+		}
+		if (!(other instanceof QuadString)) {
+			return false;
+		}
+		QuadString qs = (QuadString) other;
+		return equalsCharSequence(subject, qs.subject)
+				&& equalsCharSequence(predicate, qs.predicate)
+				&& equalsCharSequence(object, qs.object)
+				&& equalsCharSequence(context, qs.context);
+	}
+
+	@Override
+	public CharSequence getGraph() {
+		return context;
+	}
+
+	@Override
+	public void setGraph(CharSequence context) {
+		this.context = context;
+	}
+
+	@Override
+	public void setAll(CharSequence subject, CharSequence predicate, CharSequence object) {
+		setAll(subject, predicate, object, "");
+	}
+
+	/**
+	 * Sets all components at once. Useful to reuse existing object instead of
+	 * creating new ones for performance.
+	 *
+	 * @param subject   subject
+	 * @param predicate predicate
+	 * @param object    object
+	 * @param context   context
+	 */
+	public void setAll(CharSequence subject, CharSequence predicate, CharSequence object, CharSequence context) {
+		super.setAll(subject, predicate, object);
+		this.context = context;
+	}
+
+	@Override
+	public boolean match(TripleString pattern) {
+		if (context.length() != 0
+				&& !(pattern instanceof QuadString && equalsCharSequence(((QuadString) pattern).context, context))) {
+			// if a context is defined, we don't match
+			return false;
+		}
+		if (pattern.getSubject().length() == 0 || equalsCharSequence(pattern.getSubject(), this.subject)) {
+			if (pattern.getPredicate().length() == 0 || equalsCharSequence(pattern.getPredicate(), this.predicate)) {
+				return pattern.getObject().length() == 0 || equalsCharSequence(pattern.getObject(), this.object);
+			}
+		}
+		return false;
+	}
+
+	@Override
+	public boolean isEmpty() {
+		return super.isEmpty() && context.length() == 0;
+	}
+
+	@Override
+	public void read(String line) throws ParserException {
+		super.read(line, true);
+	}
+
+	@Override
+	public void read(String line, int start, int end) throws ParserException {
+		super.read(line, start, end, true);
+	}
+
+	@Override
+	public int hashCode() {
+		// Same as Objects.hashCode(subject, predicate, object), with fewer
+		// calls
+		int s = subject == null ? 0 : subject.hashCode();
+		int p = predicate == null ? 0 : predicate.hashCode();
+		int o = object == null ? 0 : object.hashCode();
+		int c = context == null ? 0 : context.hashCode();
+		return 31 * (31 * (31 * (31 * s) + p) + o) + c;
+	}
+
+	@Override
+	public QuadString tripleToString() {
+		return new QuadString(subject.toString(), predicate.toString(), object.toString(), context.toString());
+	}
+}