From dc8975149199c4e48b566ebb5051e4c45615e224 Mon Sep 17 00:00:00 2001
From: Ben Culkin <scorpress@gmail.com>
Date: Mon, 14 Dec 2020 18:23:16 -0500
Subject: Add ReverseListIterator

ReverseListIterator is a ListIterator which iterates over a given list
in reverse, so that next()/prev() are essentially swapped.
---
 src/main/java/bjc/data/ReverseListIterator.java | 72 +++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 src/main/java/bjc/data/ReverseListIterator.java

(limited to 'src/main/java/bjc')

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);
+	}
+}
-- 
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