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Diffstat (limited to 'src/org/apache/harmony/misc')
| -rw-r--r-- | src/org/apache/harmony/misc/HashCode.java | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/src/org/apache/harmony/misc/HashCode.java b/src/org/apache/harmony/misc/HashCode.java new file mode 100644 index 000000000..e8ce8f620 --- /dev/null +++ b/src/org/apache/harmony/misc/HashCode.java @@ -0,0 +1,203 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You under the Apache License, Version 2.0 + * (the "License"); you may not use this file except in compliance with + * the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.harmony.misc; + +/** + * This class is a convenience method to sequentially calculate hash code of the + * object based on the field values. The result depends on the order of elements + * appended. The exact formula is the same as for + * <code>java.util.List.hashCode</code>. + * + * If you need order independent hash code just summate, multiply or XOR all + * elements. + * + * <p> + * Suppose we have class: + * + * <pre><code> + * class Thing { + * long id; + * String name; + * float weight; + * } + * </code></pre> + * + * The hash code calculation can be expressed in 2 forms. + * + * <p> + * For maximum performance: + * + * <pre><code> + * public int hashCode() { + * int hashCode = HashCode.EMPTY_HASH_CODE; + * hashCode = HashCode.combine(hashCode, id); + * hashCode = HashCode.combine(hashCode, name); + * hashCode = HashCode.combine(hashCode, weight); + * return hashCode; + * } + * </code></pre> + * + * <p> + * For convenience: <code><pre> + * public int hashCode() { + * return new HashCode().append(id).append(name).append(weight).hashCode(); + * } + * </code></pre> + * + * @see java.util.List#hashCode() + */ +public final class HashCode { + /** + * The hashCode value before any data is appended, equals to 1. + * @see java.util.List#hashCode() + */ + public static final int EMPTY_HASH_CODE = 1; + + private int hashCode = EMPTY_HASH_CODE; + + /** + * Returns accumulated hashCode + */ + public final int hashCode() { + return hashCode; + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, boolean value) { + int v = value ? 1231 : 1237; + return combine(hashCode, v); + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, long value) { + int v = (int) (value ^ (value >>> 32)); + return combine(hashCode, v); + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, float value) { + int v = Float.floatToIntBits(value); + return combine(hashCode, v); + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, double value) { + long v = Double.doubleToLongBits(value); + return combine(hashCode, v); + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, Object value) { + return combine(hashCode, value.hashCode()); + } + + /** + * Combines hashCode of previous elements sequence and value's hashCode. + * @param hashCode previous hashCode value + * @param value new element + * @return combined hashCode + */ + public static int combine(int hashCode, int value) { + return 31 * hashCode + value; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(int value) { + hashCode = combine(hashCode, value); + return this; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(long value) { + hashCode = combine(hashCode, value); + return this; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(float value) { + hashCode = combine(hashCode, value); + return this; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(double value) { + hashCode = combine(hashCode, value); + return this; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(boolean value) { + hashCode = combine(hashCode, value); + return this; + } + + /** + * Appends value's hashCode to the current hashCode. + * @param value new element + * @return this + */ + public final HashCode append(Object value) { + hashCode = combine(hashCode, value); + return this; + } +} |