Introduce HashCodeBuilder

[yangtools.git] / common / util / src / main / java / org / opendaylight / yangtools / util / HashCodeBuilder.java

diff --git a/common/util/src/main/java/org/opendaylight/yangtools/util/HashCodeBuilder.java b/common/util/src/main/java/org/opendaylight/yangtools/util/HashCodeBuilder.java
new file mode 100644 (file)
index 0000000..874809f
--- /dev/null
+++ b/common/util/src/main/java/org/opendaylight/yangtools/util/HashCodeBuilder.java
@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) 2013 Cisco Systems, Inc. and others.  All rights reserved.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v1.0 which accompanies this distribution,
+ * and is available at http://www.eclipse.org/legal/epl-v10.html
+ */
+package org.opendaylight.yangtools.util;
+
+import org.opendaylight.yangtools.concepts.Builder;
+
+/**
+ * Utility class for incrementally building object hashCode by hashing together
+ * component objects, one by one.
+ *
+ * @param <T> Component objec type
+ */
+public final class HashCodeBuilder<T> implements Builder<Integer> {
+    private int currentHash;
+
+    /**
+     * Create a new instance, with internal hash initialized to 1,
+     * equivalent of {@link #HashCodeBuilder(1)}.
+     */
+    public HashCodeBuilder() {
+        this(1);
+    }
+
+    /**
+     * Create a new instance, with internal hash set to specified seed.
+     *
+     * @param seedHash Seed hash value
+     */
+    public HashCodeBuilder(final int seedHash) {
+        this.currentHash = seedHash;
+    }
+
+    /**
+     * Determine the next hash code combining a base hash code and the
+     * hash code of an object.
+     *
+     * @param hashCode base hash code
+     * @param obj Object to be added
+     * @return Combined hash code
+     */
+    public static int nextHashCode(final int hashCode, final Object obj) {
+        return 31 * hashCode + obj.hashCode();
+    }
+
+    /**
+     * Update the internal hash code with the hash code of a component
+     * object.
+     *
+     * @param obj Component object
+     */
+    public void addArgument(final T obj) {
+        currentHash = nextHashCode(currentHash, obj);
+    }
+
+    @Override
+    public Integer toInstance() {
+        return currentHash;
+    }
+}