Java tutorial
/* * Copyright (C) 2008 The Guava Authors * * Licensed 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 com.google.common.primitives; import static com.google.common.base.Preconditions.checkArgument; import static com.google.common.base.Preconditions.checkElementIndex; import static com.google.common.base.Preconditions.checkNotNull; import static com.google.common.base.Preconditions.checkPositionIndexes; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import java.io.Serializable; import java.util.AbstractList; import java.util.Arrays; import java.util.Collection; import java.util.Collections; import java.util.Comparator; import java.util.List; import java.util.RandomAccess; import javax.annotation.CheckReturnValue; import javax.annotation.Nullable; /** * Static utility methods pertaining to {@code boolean} primitives, that are not * already found in either {@link Boolean} or {@link Arrays}. * * <p>See the Guava User Guide article on <a href= * "https://github.com/google/guava/wiki/PrimitivesExplained"> * primitive utilities</a>. * * @author Kevin Bourrillion * @since 1.0 */ @CheckReturnValue @GwtCompatible public final class Booleans { private Booleans() { } /** * Returns a hash code for {@code value}; equal to the result of invoking * {@code ((Boolean) value).hashCode()}. * * @param value a primitive {@code boolean} value * @return a hash code for the value */ public static int hashCode(boolean value) { return value ? 1231 : 1237; } /** * Compares the two specified {@code boolean} values in the standard way * ({@code false} is considered less than {@code true}). The sign of the * value returned is the same as that of {@code ((Boolean) a).compareTo(b)}. * * <p><b>Note for Java 7 and later:</b> this method should be treated as * deprecated; use the equivalent {@link Boolean#compare} method instead. * * @param a the first {@code boolean} to compare * @param b the second {@code boolean} to compare * @return a positive number if only {@code a} is {@code true}, a negative * number if only {@code b} is true, or zero if {@code a == b} */ public static int compare(boolean a, boolean b) { return (a == b) ? 0 : (a ? 1 : -1); } /** * Returns {@code true} if {@code target} is present as an element anywhere in * {@code array}. * * <p><b>Note:</b> consider representing the array as a {@link * java.util.BitSet} instead, replacing {@code Booleans.contains(array, true)} * with {@code !bitSet.isEmpty()} and {@code Booleans.contains(array, false)} * with {@code bitSet.nextClearBit(0) == sizeOfBitSet}. * * @param array an array of {@code boolean} values, possibly empty * @param target a primitive {@code boolean} value * @return {@code true} if {@code array[i] == target} for some value of {@code * i} */ public static boolean contains(boolean[] array, boolean target) { for (boolean value : array) { if (value == target) { return true; } } return false; } /** * Returns the index of the first appearance of the value {@code target} in * {@code array}. * * <p><b>Note:</b> consider representing the array as a {@link * java.util.BitSet} instead, and using {@link * java.util.BitSet#nextSetBit(int)} or {@link * java.util.BitSet#nextClearBit(int)}. * * @param array an array of {@code boolean} values, possibly empty * @param target a primitive {@code boolean} value * @return the least index {@code i} for which {@code array[i] == target}, or * {@code -1} if no such index exists. */ public static int indexOf(boolean[] array, boolean target) { return indexOf(array, target, 0, array.length); } // TODO(kevinb): consider making this public private static int indexOf(boolean[] array, boolean target, int start, int end) { for (int i = start; i < end; i++) { if (array[i] == target) { return i; } } return -1; } /** * Returns the start position of the first occurrence of the specified {@code * target} within {@code array}, or {@code -1} if there is no such occurrence. * * <p>More formally, returns the lowest index {@code i} such that {@code * java.util.Arrays.copyOfRange(array, i, i + target.length)} contains exactly * the same elements as {@code target}. * * @param array the array to search for the sequence {@code target} * @param target the array to search for as a sub-sequence of {@code array} */ public static int indexOf(boolean[] array, boolean[] target) { checkNotNull(array, "array"); checkNotNull(target, "target"); if (target.length == 0) { return 0; } outer: for (int i = 0; i < array.length - target.length + 1; i++) { for (int j = 0; j < target.length; j++) { if (array[i + j] != target[j]) { continue outer; } } return i; } return -1; } /** * Returns the index of the last appearance of the value {@code target} in * {@code array}. * * @param array an array of {@code boolean} values, possibly empty * @param target a primitive {@code boolean} value * @return the greatest index {@code i} for which {@code array[i] == target}, * or {@code -1} if no such index exists. */ public static int lastIndexOf(boolean[] array, boolean target) { return lastIndexOf(array, target, 0, array.length); } // TODO(kevinb): consider making this public private static int lastIndexOf(boolean[] array, boolean target, int start, int end) { for (int i = end - 1; i >= start; i--) { if (array[i] == target) { return i; } } return -1; } /** * Returns the values from each provided array combined into a single array. * For example, {@code concat(new boolean[] {a, b}, new boolean[] {}, new * boolean[] {c}} returns the array {@code {a, b, c}}. * * @param arrays zero or more {@code boolean} arrays * @return a single array containing all the values from the source arrays, in * order */ public static boolean[] concat(boolean[]... arrays) { int length = 0; for (boolean[] array : arrays) { length += array.length; } boolean[] result = new boolean[length]; int pos = 0; for (boolean[] array : arrays) { System.arraycopy(array, 0, result, pos, array.length); pos += array.length; } return result; } /** * Returns an array containing the same values as {@code array}, but * guaranteed to be of a specified minimum length. If {@code array} already * has a length of at least {@code minLength}, it is returned directly. * Otherwise, a new array of size {@code minLength + padding} is returned, * containing the values of {@code array}, and zeroes in the remaining places. * * @param array the source array * @param minLength the minimum length the returned array must guarantee * @param padding an extra amount to "grow" the array by if growth is * necessary * @throws IllegalArgumentException if {@code minLength} or {@code padding} is * negative * @return an array containing the values of {@code array}, with guaranteed * minimum length {@code minLength} */ public static boolean[] ensureCapacity(boolean[] array, int minLength, int padding) { checkArgument(minLength >= 0, "Invalid minLength: %s", minLength); checkArgument(padding >= 0, "Invalid padding: %s", padding); return (array.length < minLength) ? copyOf(array, minLength + padding) : array; } // Arrays.copyOf() requires Java 6 private static boolean[] copyOf(boolean[] original, int length) { boolean[] copy = new boolean[length]; System.arraycopy(original, 0, copy, 0, Math.min(original.length, length)); return copy; } /** * Returns a string containing the supplied {@code boolean} values separated * by {@code separator}. For example, {@code join("-", false, true, false)} * returns the string {@code "false-true-false"}. * * @param separator the text that should appear between consecutive values in * the resulting string (but not at the start or end) * @param array an array of {@code boolean} values, possibly empty */ public static String join(String separator, boolean... array) { checkNotNull(separator); if (array.length == 0) { return ""; } // For pre-sizing a builder, just get the right order of magnitude StringBuilder builder = new StringBuilder(array.length * 7); builder.append(array[0]); for (int i = 1; i < array.length; i++) { builder.append(separator).append(array[i]); } return builder.toString(); } /** * Returns a comparator that compares two {@code boolean} arrays * lexicographically. That is, it compares, using {@link * #compare(boolean, boolean)}), the first pair of values that follow any * common prefix, or when one array is a prefix of the other, treats the * shorter array as the lesser. For example, * {@code [] < [false] < [false, true] < [true]}. * * <p>The returned comparator is inconsistent with {@link * Object#equals(Object)} (since arrays support only identity equality), but * it is consistent with {@link Arrays#equals(boolean[], boolean[])}. * * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order"> * Lexicographical order article at Wikipedia</a> * @since 2.0 */ public static Comparator<boolean[]> lexicographicalComparator() { return LexicographicalComparator.INSTANCE; } private enum LexicographicalComparator implements Comparator<boolean[]> { INSTANCE; @Override public int compare(boolean[] left, boolean[] right) { int minLength = Math.min(left.length, right.length); for (int i = 0; i < minLength; i++) { int result = Booleans.compare(left[i], right[i]); if (result != 0) { return result; } } return left.length - right.length; } } /** * Copies a collection of {@code Boolean} instances into a new array of * primitive {@code boolean} values. * * <p>Elements are copied from the argument collection as if by {@code * collection.toArray()}. Calling this method is as thread-safe as calling * that method. * * <p><b>Note:</b> consider representing the collection as a {@link * java.util.BitSet} instead. * * @param collection a collection of {@code Boolean} objects * @return an array containing the same values as {@code collection}, in the * same order, converted to primitives * @throws NullPointerException if {@code collection} or any of its elements * is null */ public static boolean[] toArray(Collection<Boolean> collection) { if (collection instanceof BooleanArrayAsList) { return ((BooleanArrayAsList) collection).toBooleanArray(); } Object[] boxedArray = collection.toArray(); int len = boxedArray.length; boolean[] array = new boolean[len]; for (int i = 0; i < len; i++) { // checkNotNull for GWT (do not optimize) array[i] = (Boolean) checkNotNull(boxedArray[i]); } return array; } /** * Returns a fixed-size list backed by the specified array, similar to {@link * Arrays#asList(Object[])}. The list supports {@link List#set(int, Object)}, * but any attempt to set a value to {@code null} will result in a {@link * NullPointerException}. * * <p>The returned list maintains the values, but not the identities, of * {@code Boolean} objects written to or read from it. For example, whether * {@code list.get(0) == list.get(0)} is true for the returned list is * unspecified. * * @param backingArray the array to back the list * @return a list view of the array */ public static List<Boolean> asList(boolean... backingArray) { if (backingArray.length == 0) { return Collections.emptyList(); } return new BooleanArrayAsList(backingArray); } @GwtCompatible private static class BooleanArrayAsList extends AbstractList<Boolean> implements RandomAccess, Serializable { final boolean[] array; final int start; final int end; BooleanArrayAsList(boolean[] array) { this(array, 0, array.length); } BooleanArrayAsList(boolean[] array, int start, int end) { this.array = array; this.start = start; this.end = end; } @Override public int size() { return end - start; } @Override public boolean isEmpty() { return false; } @Override public Boolean get(int index) { checkElementIndex(index, size()); return array[start + index]; } @Override public boolean contains(Object target) { // Overridden to prevent a ton of boxing return (target instanceof Boolean) && Booleans.indexOf(array, (Boolean) target, start, end) != -1; } @Override public int indexOf(Object target) { // Overridden to prevent a ton of boxing if (target instanceof Boolean) { int i = Booleans.indexOf(array, (Boolean) target, start, end); if (i >= 0) { return i - start; } } return -1; } @Override public int lastIndexOf(Object target) { // Overridden to prevent a ton of boxing if (target instanceof Boolean) { int i = Booleans.lastIndexOf(array, (Boolean) target, start, end); if (i >= 0) { return i - start; } } return -1; } @Override public Boolean set(int index, Boolean element) { checkElementIndex(index, size()); boolean oldValue = array[start + index]; // checkNotNull for GWT (do not optimize) array[start + index] = checkNotNull(element); return oldValue; } @Override public List<Boolean> subList(int fromIndex, int toIndex) { int size = size(); checkPositionIndexes(fromIndex, toIndex, size); if (fromIndex == toIndex) { return Collections.emptyList(); } return new BooleanArrayAsList(array, start + fromIndex, start + toIndex); } @Override public boolean equals(@Nullable Object object) { if (object == this) { return true; } if (object instanceof BooleanArrayAsList) { BooleanArrayAsList that = (BooleanArrayAsList) object; int size = size(); if (that.size() != size) { return false; } for (int i = 0; i < size; i++) { if (array[start + i] != that.array[that.start + i]) { return false; } } return true; } return super.equals(object); } @Override public int hashCode() { int result = 1; for (int i = start; i < end; i++) { result = 31 * result + Booleans.hashCode(array[i]); } return result; } @Override public String toString() { StringBuilder builder = new StringBuilder(size() * 7); builder.append(array[start] ? "[true" : "[false"); for (int i = start + 1; i < end; i++) { builder.append(array[i] ? ", true" : ", false"); } return builder.append(']').toString(); } boolean[] toBooleanArray() { // Arrays.copyOfRange() is not available under GWT int size = size(); boolean[] result = new boolean[size]; System.arraycopy(array, start, result, 0, size); return result; } private static final long serialVersionUID = 0; } /** * Returns the number of {@code values} that are {@code true}. * * @since 16.0 */ @Beta public static int countTrue(boolean... values) { int count = 0; for (boolean value : values) { if (value) { count++; } } return count; } }