Added TimedHashSet that entries have limited TTL

src/zutil/struct/TimedHashSet.java

@@ -0,0 +1,52 @@
+package zutil.struct;
+
+import java.util.AbstractSet;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Iterator;
+
+/**
+ * This is a timed HashSet. Each entry has a limited time to live.
+ */
+public class TimedHashSet<T> {
+
+    private HashMap<T, Long> map;
+    private long ttl;
+
+    /**
+     * @param   ttl     milliseconds the entries will live
+     */
+    public TimedHashSet(long ttl){
+        this.ttl = ttl;
+        this.map = new HashMap<>();
+    }
+
+
+    /**
+     * @return true if the object already existed in the set which will reset the TTL.
+     */
+    public boolean add(T o){
+        return map.put(o, System.currentTimeMillis()) != null;
+    }
+
+    public boolean contains(Object o){
+        if(map.containsKey(o)){
+            if(map.get(o) + ttl < System.currentTimeMillis()) // entry to old
+                map.remove(o);
+            else
+                return true;
+        }
+        return false;
+    }
+
+
+    /**
+     * Iterates through the Set and removes all entries that has passed the TTL
+     */
+    public void garbageCollect(){
+        for(T o : map.keySet()){
+            if(map.get(o) + ttl < System.currentTimeMillis()) // entry to old
+                map.remove(o);
+        }
+    }
+}

test/zutil/test/TimedHashSetTest.java

@@ -0,0 +1,39 @@
+package zutil.test;
+
+import org.junit.Test;
+import zutil.struct.TimedHashSet;
+
+import static org.junit.Assert.*;
+
+/**
+ * Created by Ziver on 2015-11-20.
+ */
+public class TimedHashSetTest {
+    public static final String ENTRY = "key";
+
+    @Test
+    public void zeroTTL() throws InterruptedException {
+        TimedHashSet set = new TimedHashSet(0);
+        set.add(ENTRY);
+        Thread.sleep(1);
+        assertFalse(set.contains(ENTRY));
+    }
+
+    @Test
+    public void tenMsTTL() throws InterruptedException {
+        TimedHashSet set = new TimedHashSet(10);
+        set.add(ENTRY);
+        Thread.sleep(1);
+        assert(set.contains(ENTRY));
+        Thread.sleep(10);
+        assertFalse(set.contains(ENTRY));
+    }
+
+    @Test
+    public void oneSecTTL() throws InterruptedException {
+        TimedHashSet set = new TimedHashSet(1000);
+        set.add(ENTRY);
+        Thread.sleep(1);
+        assert(set.contains(ENTRY));
+    }
+}