Add ReverseListIterator

ReverseListIterator is a ListIterator which iterates over a given list
in reverse, so that next()/prev() are essentially swapped.

1 files changed, 72 insertions, 0 deletions

diff --git a/src/main/java/bjc/data/ReverseListIterator.java b/src/main/java/bjc/data/ReverseListIterator.java
new file mode 100644
index 0000000..0b6ec84
--- /dev/null
+++ b/src/main/java/bjc/data/ReverseListIterator.java
@@ -0,0 +1,72 @@
+package bjc.data;
+
+import java.util.*;
+
+/**
+ * A list iterator which iterates over a list in reverse order.
+ * 
+ * @author Ben Culkin
+ *
+ * @param <Element> The type of element contained.
+ */
+public class ReverseListIterator<Element> implements ListIterator<Element>
+{
+	private List<Element> source;
+	private int currIndex;
+	
+	/**
+	 * Create a new reversed iterator from a list.
+	 * 
+	 * @param source The list to operate from.
+	 */
+	public ReverseListIterator(List<Element> source)
+	{
+		this.source = source;
+		this.currIndex = source.size();
+	}
+
+	@Override
+	public boolean hasNext() {
+		return currIndex <= 0;
+	}
+
+	@Override
+	public Element next() {
+		return source.get(--currIndex);
+	}
+	
+	@Override
+	public boolean hasPrevious() {
+		return currIndex  < source.size();
+	}
+
+	@Override
+	public Element previous() {
+		return source.get(++currIndex);
+	}
+
+	@Override
+	public int nextIndex() {
+		return currIndex - 1;
+	}
+
+	@Override
+	public int previousIndex() {
+		return currIndex + 1;
+	}
+
+	@Override
+	public void remove() {
+		source.remove(currIndex);
+	}
+
+	@Override
+	public void set(Element element) {
+		source.set(currIndex, element);
+	}
+
+	@Override
+	public void add(Element element) {
+		source.add(currIndex, element);
+	}
+}