Slice out LinkKey

Change-Id: Ibfcafd07858c5357a2321220e01ddab44f347923
diff --git a/core/api/src/main/java/org/onlab/onos/net/LinkKey.java b/core/api/src/main/java/org/onlab/onos/net/LinkKey.java
new file mode 100644
index 0000000..dee4e88
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/net/LinkKey.java
@@ -0,0 +1,71 @@
+package org.onlab.onos.net;
+
+import java.util.Objects;
+
+import com.google.common.base.MoreObjects;
+
+// TODO Consider renaming.
+// it's an identifier for a Link, but it's not ElementId, so not using LinkId.
+/**
+ * Immutable representation of a link identity.
+ */
+public class LinkKey {
+
+    private final ConnectPoint src;
+    private final ConnectPoint dst;
+
+    /**
+     * Returns source connection point.
+     *
+     * @return source connection point
+     */
+    public ConnectPoint src() {
+        return src;
+    }
+
+    /**
+     * Returns destination connection point.
+     *
+     * @return destination connection point
+     */
+    public ConnectPoint dst() {
+        return dst;
+    }
+
+    /**
+     * Creates a link identifier with source and destination connection point.
+     *
+     * @param src source connection point
+     * @param dst destination connection point
+     */
+    public LinkKey(ConnectPoint src, ConnectPoint dst) {
+        this.src = src;
+        this.dst = dst;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(src(), dst);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj instanceof LinkKey) {
+            final LinkKey other = (LinkKey) obj;
+            return Objects.equals(this.src(), other.src()) &&
+                    Objects.equals(this.dst, other.dst);
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(getClass())
+                .add("src", src())
+                .add("dst", dst)
+                .toString();
+    }
+}