StringKeyAnalyzer.java
- /*
- * 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.commons.collections4.trie.analyzer;
- import org.apache.commons.collections4.trie.KeyAnalyzer;
- /**
- * An {@link KeyAnalyzer} for {@link String}s.
- * <p>
- * This class is stateless.
- * </p>
- * @since 4.0
- */
- public class StringKeyAnalyzer extends KeyAnalyzer<String> {
- private static final long serialVersionUID = -7032449491269434877L;
- /** A singleton instance of {@link StringKeyAnalyzer}. */
- public static final StringKeyAnalyzer INSTANCE = new StringKeyAnalyzer();
- /** The number of bits per {@link Character}. */
- public static final int LENGTH = Character.SIZE;
- /** A bit mask where the first bit is 1 and the others are zero. */
- private static final int MSB = 0x8000;
- /** Returns a bit mask where the given bit is set. */
- private static int mask(final int bit) {
- return MSB >>> bit;
- }
- /**
- * Constructs a new instance.
- *
- * @deprecated Use {@link #INSTANCE}.
- */
- @Deprecated
- public StringKeyAnalyzer() {
- // empty
- }
- @Override
- public int bitIndex(final String key, final int offsetInBits, final int lengthInBits,
- final String other, final int otherOffsetInBits, final int otherLengthInBits) {
- boolean allNull = true;
- if (offsetInBits % LENGTH != 0 || otherOffsetInBits % LENGTH != 0
- || lengthInBits % LENGTH != 0 || otherLengthInBits % LENGTH != 0) {
- throw new IllegalArgumentException("The offsets and lengths must be at Character boundaries");
- }
- final int beginIndex1 = offsetInBits / LENGTH;
- final int beginIndex2 = otherOffsetInBits / LENGTH;
- final int endIndex1 = beginIndex1 + lengthInBits / LENGTH;
- final int endIndex2 = beginIndex2 + otherLengthInBits / LENGTH;
- final int length = Math.max(endIndex1, endIndex2);
- // Look at each character, and if they're different
- // then figure out which bit makes the difference
- // and return it.
- char k = 0;
- char f = 0;
- for (int i = 0; i < length; i++) {
- final int index1 = beginIndex1 + i;
- final int index2 = beginIndex2 + i;
- if (index1 >= endIndex1) {
- k = 0;
- } else {
- k = key.charAt(index1);
- }
- if (other == null || index2 >= endIndex2) {
- f = 0;
- } else {
- f = other.charAt(index2);
- }
- if (k != f) {
- final int x = k ^ f;
- return i * LENGTH + Integer.numberOfLeadingZeros(x) - LENGTH;
- }
- if (k != 0) {
- allNull = false;
- }
- }
- // All bits are 0
- if (allNull) {
- return NULL_BIT_KEY;
- }
- // Both keys are equal
- return EQUAL_BIT_KEY;
- }
- @Override
- public int bitsPerElement() {
- return LENGTH;
- }
- @Override
- public boolean isBitSet(final String key, final int bitIndex, final int lengthInBits) {
- if (key == null || bitIndex >= lengthInBits) {
- return false;
- }
- final int index = bitIndex / LENGTH;
- final int bit = bitIndex % LENGTH;
- return (key.charAt(index) & mask(bit)) != 0;
- }
- @Override
- public boolean isPrefix(final String prefix, final int offsetInBits,
- final int lengthInBits, final String key) {
- if (offsetInBits % LENGTH != 0 || lengthInBits % LENGTH != 0) {
- throw new IllegalArgumentException(
- "Cannot determine prefix outside of Character boundaries");
- }
- final String s1 = prefix.substring(offsetInBits / LENGTH, lengthInBits / LENGTH);
- return key.startsWith(s1);
- }
- @Override
- public int lengthInBits(final String key) {
- return key != null ? key.length() * LENGTH : 0;
- }
- }