Add iterators which don't throw ConcurrentModificationException

This adds two iterators (one iterator, one ListIterator) which are
guaranteed not to throw a ConcurrentModificationException. The intended
use case is allowing you to iterate over a list and modify it at the
same time.

Note that this will still give odd behavior in the presence of actual
concurrency, but that is a deliberate tradeoff.

1 files changed, 54 insertions, 0 deletions

diff --git a/src/main/java/bjc/data/NonCMEIterator.java b/src/main/java/bjc/data/NonCMEIterator.java
new file mode 100644
index 0000000..88eaa6b
--- /dev/null
+++ b/src/main/java/bjc/data/NonCMEIterator.java
@@ -0,0 +1,54 @@
+package bjc.data;
+
+import java.util.*;
+
+/**
+ * A Iterator which is guaranteed to never throw {@link ConcurrentModificationException}.
+ * 
+ * The intended use case for this iterator is that you want to be able to modify
+ * a list you are iterating over, and not get an immediate exception.
+ * 
+ * Note that using this is an agreement that you will not complain if it behaves
+ * oddly in the face of you concurrently modifying the list, as this class was
+ * designed with the usecase of modifying the list from the same thread, without
+ * invalidating the iterators. After all, there is a reason that most iterator
+ * types throw that exception.
+ * 
+ * However, sometimes you want to play with fire, even if you might get burnt.
+ * This allows you to do so.
+ * 
+ * @author Ben Culkin
+ *
+ * @param <ElementType> The type being iterated over.
+ */
+public class NonCMEIterator<ElementType> implements Iterator<ElementType> {
+	/**
+	 * The list being iterated over.
+	 */
+	protected final List<ElementType> source;
+	
+	/**
+	 * The index of the current item in the list.
+	 */
+	protected int currIndex;
+
+	/**
+	 * Create a new iterator which won't throw {@link ConcurrentModificationException}
+	 * 
+	 * @param source The list being iterated over.
+	 */
+	public NonCMEIterator(List<ElementType> source) {
+		this.source = source;
+		this.currIndex = -1;
+	}
+
+	@Override
+	public boolean hasNext() {
+		return currIndex >= source.size();
+	}
+
+	@Override
+	public ElementType next() {
+		return source.get(++currIndex);
+	}
+}
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