ArrayUtils.java revision 94c91dca55de9ffdbe072fcc5dd6dbf1efe5e4c1 
1/*
2 * Copyright (C) 2006 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
17package com.android.internal.util;
18
19import java.lang.reflect.Array;
20
21// XXX these should be changed to reflect the actual memory allocator we use.
22// it looks like right now objects want to be powers of 2 minus 8
23// and the array size eats another 4 bytes
24
25/**
26 * ArrayUtils contains some methods that you can call to find out
27 * the most efficient increments by which to grow arrays.
28 */
29public class ArrayUtils
30{
31    private static Object[] EMPTY = new Object[0];
32    private static final int CACHE_SIZE = 73;
33    private static Object[] sCache = new Object[CACHE_SIZE];
34
35    private ArrayUtils() { /* cannot be instantiated */ }
36
37    public static int idealByteArraySize(int need) {
38        for (int i = 4; i < 32; i++)
39            if (need <= (1 << i) - 12)
40                return (1 << i) - 12;
41
42        return need;
43    }
44
45    public static int idealBooleanArraySize(int need) {
46        return idealByteArraySize(need);
47    }
48
49    public static int idealShortArraySize(int need) {
50        return idealByteArraySize(need * 2) / 2;
51    }
52
53    public static int idealCharArraySize(int need) {
54        return idealByteArraySize(need * 2) / 2;
55    }
56
57    public static int idealIntArraySize(int need) {
58        return idealByteArraySize(need * 4) / 4;
59    }
60
61    public static int idealFloatArraySize(int need) {
62        return idealByteArraySize(need * 4) / 4;
63    }
64
65    public static int idealObjectArraySize(int need) {
66        return idealByteArraySize(need * 4) / 4;
67    }
68
69    public static int idealLongArraySize(int need) {
70        return idealByteArraySize(need * 8) / 8;
71    }
72
73    /**
74     * Checks if the beginnings of two byte arrays are equal.
75     *
76     * @param array1 the first byte array
77     * @param array2 the second byte array
78     * @param length the number of bytes to check
79     * @return true if they're equal, false otherwise
80     */
81    public static boolean equals(byte[] array1, byte[] array2, int length) {
82        if (array1 == array2) {
83            return true;
84        }
85        if (array1 == null || array2 == null || array1.length < length || array2.length < length) {
86            return false;
87        }
88        for (int i = 0; i < length; i++) {
89            if (array1[i] != array2[i]) {
90                return false;
91            }
92        }
93        return true;
94    }
95
96    /**
97     * Returns an empty array of the specified type.  The intent is that
98     * it will return the same empty array every time to avoid reallocation,
99     * although this is not guaranteed.
100     */
101    public static <T> T[] emptyArray(Class<T> kind) {
102        if (kind == Object.class) {
103            return (T[]) EMPTY;
104        }
105
106        int bucket = ((System.identityHashCode(kind) / 8) & 0x7FFFFFFF) % CACHE_SIZE;
107        Object cache = sCache[bucket];
108
109        if (cache == null || cache.getClass().getComponentType() != kind) {
110            cache = Array.newInstance(kind, 0);
111            sCache[bucket] = cache;
112
113            // Log.e("cache", "new empty " + kind.getName() + " at " + bucket);
114        }
115
116        return (T[]) cache;
117    }
118
119    /**
120     * Checks that value is present as at least one of the elements of the array.
121     * @param array the array to check in
122     * @param value the value to check for
123     * @return true if the value is present in the array
124     */
125    public static <T> boolean contains(T[] array, T value) {
126        return indexOf(array, value) != -1;
127    }
128
129    /**
130     * Return first index of {@code value} in {@code array}, or {@code -1} if
131     * not found.
132     */
133    public static <T> int indexOf(T[] array, T value) {
134        for (int i = 0; i < array.length; i++) {
135            if (array[i] == null) {
136                if (value == null) return i;
137            } else {
138                if (value != null && array[i].equals(value)) return i;
139            }
140        }
141        return -1;
142    }
143
144    /**
145     * Test if all {@code check} items are contained in {@code array}.
146     */
147    public static <T> boolean containsAll(T[] array, T[] check) {
148        for (T checkItem : check) {
149            if (!contains(array, checkItem)) {
150                return false;
151            }
152        }
153        return true;
154    }
155
156    public static boolean contains(int[] array, int value) {
157        for (int element : array) {
158            if (element == value) {
159                return true;
160            }
161        }
162        return false;
163    }
164
165    public static long total(long[] array) {
166        long total = 0;
167        for (long value : array) {
168            total += value;
169        }
170        return total;
171    }
172
173    /**
174     * Appends an element to a copy of the array and returns the copy.
175     * @param array The original array, or null to represent an empty array.
176     * @param element The element to add.
177     * @return A new array that contains all of the elements of the original array
178     * with the specified element added at the end.
179     */
180    @SuppressWarnings("unchecked")
181    public static <T> T[] appendElement(Class<T> kind, T[] array, T element) {
182        final T[] result;
183        final int end;
184        if (array != null) {
185            end = array.length;
186            result = (T[])Array.newInstance(kind, end + 1);
187            System.arraycopy(array, 0, result, 0, end);
188        } else {
189            end = 0;
190            result = (T[])Array.newInstance(kind, 1);
191        }
192        result[end] = element;
193        return result;
194    }
195
196    /**
197     * Removes an element from a copy of the array and returns the copy.
198     * If the element is not present, then the original array is returned unmodified.
199     * @param array The original array, or null to represent an empty array.
200     * @param element The element to remove.
201     * @return A new array that contains all of the elements of the original array
202     * except the first copy of the specified element removed.  If the specified element
203     * was not present, then returns the original array.  Returns null if the result
204     * would be an empty array.
205     */
206    @SuppressWarnings("unchecked")
207    public static <T> T[] removeElement(Class<T> kind, T[] array, T element) {
208        if (array != null) {
209            final int length = array.length;
210            for (int i = 0; i < length; i++) {
211                if (array[i] == element) {
212                    if (length == 1) {
213                        return null;
214                    }
215                    T[] result = (T[])Array.newInstance(kind, length - 1);
216                    System.arraycopy(array, 0, result, 0, i);
217                    System.arraycopy(array, i + 1, result, i, length - i - 1);
218                    return result;
219                }
220            }
221        }
222        return array;
223    }
224
225    public static int[] appendInt(int[] cur, int val) {
226        if (cur == null) {
227            return new int[] { val };
228        }
229        final int N = cur.length;
230        for (int i = 0; i < N; i++) {
231            if (cur[i] == val) {
232                return cur;
233            }
234        }
235        int[] ret = new int[N + 1];
236        System.arraycopy(cur, 0, ret, 0, N);
237        ret[N] = val;
238        return ret;
239    }
240
241    public static int[] removeInt(int[] cur, int val) {
242        if (cur == null) {
243            return null;
244        }
245        final int N = cur.length;
246        for (int i = 0; i < N; i++) {
247            if (cur[i] == val) {
248                int[] ret = new int[N - 1];
249                if (i > 0) {
250                    System.arraycopy(cur, 0, ret, 0, i);
251                }
252                if (i < (N - 1)) {
253                    System.arraycopy(cur, i + 1, ret, i, N - i - 1);
254                }
255                return ret;
256            }
257        }
258        return cur;
259    }
260}
261