Merge branch 'multiset' into 'master'

Use a multiset for counting things

See merge request akwizgran/briar!688

bramble-api/src/main/java/org/briarproject/bramble/api/Multiset.java

@@ -0,0 +1,101 @@
+package org.briarproject.bramble.api;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.NoSuchElementException;
+import java.util.Set;
+
+import javax.annotation.concurrent.NotThreadSafe;
+
+@NotThreadSafe
+@NotNullByDefault
+public class Multiset<T> {
+
+	private final Map<T, Integer> map = new HashMap<>();
+
+	private int total = 0;
+
+	/**
+	 * Returns how many items the multiset contains in total.
+	 */
+	public int getTotal() {
+		return total;
+	}
+
+	/**
+	 * Returns how many unique items the multiset contains.
+	 */
+	public int getUnique() {
+		return map.size();
+	}
+
+	/**
+	 * Returns how many of the given item the multiset contains.
+	 */
+	public int getCount(T t) {
+		Integer count = map.get(t);
+		return count == null ? 0 : count;
+	}
+
+	/**
+	 * Adds the given item to the multiset and returns how many of the item
+	 * the multiset now contains.
+	 */
+	public int add(T t) {
+		Integer count = map.get(t);
+		if (count == null) count = 0;
+		map.put(t, count + 1);
+		total++;
+		return count + 1;
+	}
+
+	/**
+	 * Removes the given item from the multiset and returns how many of the
+	 * item the multiset now contains.
+	 * @throws NoSuchElementException if the item is not in the multiset.
+	 */
+	public int remove(T t) {
+		Integer count = map.get(t);
+		if (count == null) throw new NoSuchElementException();
+		if (count == 1) map.remove(t);
+		else map.put(t, count - 1);
+		total--;
+		return count - 1;
+	}
+
+	/**
+	 * Removes all occurrences of the given item from the multiset.
+	 */
+	public int removeAll(T t) {
+		Integer count = map.remove(t);
+		if (count == null) return 0;
+		total -= count;
+		return count;
+	}
+
+	/**
+	 * Returns true if the multiset contains any occurrences of the given item.
+	 */
+	public boolean contains(T t) {
+		return map.containsKey(t);
+	}
+
+	/**
+	 * Removes all items from the multiset.
+	 */
+	public void clear() {
+		map.clear();
+		total = 0;
+	}
+
+	/**
+	 * Returns the set of unique items the multiset contains. The returned set
+	 * is unmodifiable.
+	 */
+	public Set<T> keySet() {
+		return Collections.unmodifiableSet(map.keySet());
+	}
+}