1 /* 2 * Copyright (C) 2010 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package libcore.internal; 18 19 /** 20 * A pool of string instances. Unlike the {@link String#intern() VM's 21 * interned strings}, this pool provides no guarantee of reference equality. 22 * It is intended only to save allocations. This class is not thread safe. 23 */ 24 public final class StringPool { 25 26 private final String[] pool = new String[512]; 27 contentEquals(String s, char[] chars, int start, int length)28 private static boolean contentEquals(String s, char[] chars, int start, int length) { 29 if (s.length() != length) { 30 return false; 31 } 32 for (int i = 0; i < length; i++) { 33 if (chars[start + i] != s.charAt(i)) { 34 return false; 35 } 36 } 37 return true; 38 } 39 40 /** 41 * Returns a string equal to {@code new String(array, start, length)}. 42 */ get(char[] array, int start, int length)43 public String get(char[] array, int start, int length) { 44 // Compute an arbitrary hash of the content 45 int hashCode = 0; 46 for (int i = start; i < start + length; i++) { 47 hashCode = (hashCode * 31) + array[i]; 48 } 49 50 // Pick a bucket using Doug Lea's supplemental secondaryHash function (from HashMap) 51 hashCode ^= (hashCode >>> 20) ^ (hashCode >>> 12); 52 hashCode ^= (hashCode >>> 7) ^ (hashCode >>> 4); 53 int index = hashCode & (pool.length - 1); 54 55 String pooled = pool[index]; 56 if (pooled != null && contentEquals(pooled, array, start, length)) { 57 return pooled; 58 } 59 60 String result = new String(array, start, length); 61 pool[index] = result; 62 return result; 63 } 64 } 65