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.GwtCompatible; import com.google.common.annotations.GwtIncompatible; 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 char} primitives, that are not * already found in either {@link Character} or {@link Arrays}. * * <p>All the operations in this class treat {@code char} values strictly * numerically; they are neither Unicode-aware nor locale-dependent. * * <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(emulated = true) public final class Chars { private Chars() { } /** * The number of bytes required to represent a primitive {@code char} * value. */ public static final int BYTES = Character.SIZE / Byte.SIZE; /** * Returns a hash code for {@code value}; equal to the result of invoking * {@code ((Character) value).hashCode()}. * * @param value a primitive {@code char} value * @return a hash code for the value */ public static int hashCode(char value) { return value; } /** * Returns the {@code char} value that is equal to {@code value}, if possible. * * @param value any value in the range of the {@code char} type * @return the {@code char} value that equals {@code value} * @throws IllegalArgumentException if {@code value} is greater than {@link * Character#MAX_VALUE} or less than {@link Character#MIN_VALUE} */ public static char checkedCast(long value) { char result = (char) value; if (result != value) { // don't use checkArgument here, to avoid boxing throw new IllegalArgumentException("Out of range: " + value); } return result; } /** * Returns the {@code char} nearest in value to {@code value}. * * @param value any {@code long} value * @return the same value cast to {@code char} if it is in the range of the * {@code char} type, {@link Character#MAX_VALUE} if it is too large, * or {@link Character#MIN_VALUE} if it is too small */ public static char saturatedCast(long value) { if (value > Character.MAX_VALUE) { return Character.MAX_VALUE; } if (value < Character.MIN_VALUE) { return Character.MIN_VALUE; } return (char) value; } /** * Compares the two specified {@code char} values. The sign of the value * returned is the same as that of {@code ((Character) a).compareTo(b)}. * * <p><b>Note for Java 7 and later:</b> this method should be treated as * deprecated; use the equivalent {@link Character#compare} method instead. * * @param a the first {@code char} to compare * @param b the second {@code char} to compare * @return a negative value if {@code a} is less than {@code b}; a positive * value if {@code a} is greater than {@code b}; or zero if they are equal */ public static int compare(char a, char b) { return a - b; // safe due to restricted range } /** * Returns {@code true} if {@code target} is present as an element anywhere in * {@code array}. * * @param array an array of {@code char} values, possibly empty * @param target a primitive {@code char} value * @return {@code true} if {@code array[i] == target} for some value of {@code * i} */ public static boolean contains(char[] array, char target) { for (char value : array) { if (value == target) { return true; } } return false; } /** * Returns the index of the first appearance of the value {@code target} in * {@code array}. * * @param array an array of {@code char} values, possibly empty * @param target a primitive {@code char} 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(char[] array, char target) { return indexOf(array, target, 0, array.length); } // TODO(kevinb): consider making this public private static int indexOf(char[] array, char 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(char[] array, char[] 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 char} values, possibly empty * @param target a primitive {@code char} 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(char[] array, char target) { return lastIndexOf(array, target, 0, array.length); } // TODO(kevinb): consider making this public private static int lastIndexOf(char[] array, char target, int start, int end) { for (int i = end - 1; i >= start; i--) { if (array[i] == target) { return i; } } return -1; } /** * Returns the least value present in {@code array}. * * @param array a <i>nonempty</i> array of {@code char} values * @return the value present in {@code array} that is less than or equal to * every other value in the array * @throws IllegalArgumentException if {@code array} is empty */ public static char min(char... array) { checkArgument(array.length > 0); char min = array[0]; for (int i = 1; i < array.length; i++) { if (array[i] < min) { min = array[i]; } } return min; } /** * Returns the greatest value present in {@code array}. * * @param array a <i>nonempty</i> array of {@code char} values * @return the value present in {@code array} that is greater than or equal to * every other value in the array * @throws IllegalArgumentException if {@code array} is empty */ public static char max(char... array) { checkArgument(array.length > 0); char max = array[0]; for (int i = 1; i < array.length; i++) { if (array[i] > max) { max = array[i]; } } return max; } /** * Returns the values from each provided array combined into a single array. * For example, {@code concat(new char[] {a, b}, new char[] {}, new * char[] {c}} returns the array {@code {a, b, c}}. * * @param arrays zero or more {@code char} arrays * @return a single array containing all the values from the source arrays, in * order */ public static char[] concat(char[]... arrays) { int length = 0; for (char[] array : arrays) { length += array.length; } char[] result = new char[length]; int pos = 0; for (char[] array : arrays) { System.arraycopy(array, 0, result, pos, array.length); pos += array.length; } return result; } /** * Returns a big-endian representation of {@code value} in a 2-element byte * array; equivalent to {@code * ByteBuffer.allocate(2).putChar(value).array()}. For example, the input * value {@code '\\u5432'} would yield the byte array {@code {0x54, 0x32}}. * * <p>If you need to convert and concatenate several values (possibly even of * different types), use a shared {@link java.nio.ByteBuffer} instance, or use * {@link com.google.common.io.ByteStreams#newDataOutput()} to get a growable * buffer. */ @GwtIncompatible("doesn't work") public static byte[] toByteArray(char value) { return new byte[] { (byte) (value >> 8), (byte) value }; } /** * Returns the {@code char} value whose big-endian representation is * stored in the first 2 bytes of {@code bytes}; equivalent to {@code * ByteBuffer.wrap(bytes).getChar()}. For example, the input byte array * {@code {0x54, 0x32}} would yield the {@code char} value {@code '\\u5432'}. * * <p>Arguably, it's preferable to use {@link java.nio.ByteBuffer}; that * library exposes much more flexibility at little cost in readability. * * @throws IllegalArgumentException if {@code bytes} has fewer than 2 * elements */ @GwtIncompatible("doesn't work") public static char fromByteArray(byte[] bytes) { checkArgument(bytes.length >= BYTES, "array too small: %s < %s", bytes.length, BYTES); return fromBytes(bytes[0], bytes[1]); } /** * Returns the {@code char} value whose byte representation is the given 2 * bytes, in big-endian order; equivalent to {@code Chars.fromByteArray(new * byte[] {b1, b2})}. * * @since 7.0 */ @GwtIncompatible("doesn't work") public static char fromBytes(byte b1, byte b2) { return (char) ((b1 << 8) | (b2 & 0xFF)); } /** * 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 char[] ensureCapacity(char[] 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 char[] copyOf(char[] original, int length) { char[] copy = new char[length]; System.arraycopy(original, 0, copy, 0, Math.min(original.length, length)); return copy; } /** * Returns a string containing the supplied {@code char} values separated * by {@code separator}. For example, {@code join("-", '1', '2', '3')} returns * the string {@code "1-2-3"}. * * @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 char} values, possibly empty */ public static String join(String separator, char... array) { checkNotNull(separator); int len = array.length; if (len == 0) { return ""; } StringBuilder builder = new StringBuilder(len + separator.length() * (len - 1)); builder.append(array[0]); for (int i = 1; i < len; i++) { builder.append(separator).append(array[i]); } return builder.toString(); } /** * Returns a comparator that compares two {@code char} arrays * lexicographically. That is, it compares, using {@link * #compare(char, char)}), 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 [] < ['a'] < ['a', 'b'] < ['b']}. * * <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(char[], char[])}. * * @see <a href="http://en.wikipedia.org/wiki/Lexicographical_order"> * Lexicographical order article at Wikipedia</a> * @since 2.0 */ public static Comparator<char[]> lexicographicalComparator() { return LexicographicalComparator.INSTANCE; } private enum LexicographicalComparator implements Comparator<char[]> { INSTANCE; @Override public int compare(char[] left, char[] right) { int minLength = Math.min(left.length, right.length); for (int i = 0; i < minLength; i++) { int result = Chars.compare(left[i], right[i]); if (result != 0) { return result; } } return left.length - right.length; } } /** * Copies a collection of {@code Character} instances into a new array of * primitive {@code char} 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. * * @param collection a collection of {@code Character} 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 char[] toArray(Collection<Character> collection) { if (collection instanceof CharArrayAsList) { return ((CharArrayAsList) collection).toCharArray(); } Object[] boxedArray = collection.toArray(); int len = boxedArray.length; char[] array = new char[len]; for (int i = 0; i < len; i++) { // checkNotNull for GWT (do not optimize) array[i] = (Character) 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 Character} 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<Character> asList(char... backingArray) { if (backingArray.length == 0) { return Collections.emptyList(); } return new CharArrayAsList(backingArray); } @GwtCompatible private static class CharArrayAsList extends AbstractList<Character> implements RandomAccess, Serializable { final char[] array; final int start; final int end; CharArrayAsList(char[] array) { this(array, 0, array.length); } CharArrayAsList(char[] 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 Character 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 Character) && Chars.indexOf(array, (Character) target, start, end) != -1; } @Override public int indexOf(Object target) { // Overridden to prevent a ton of boxing if (target instanceof Character) { int i = Chars.indexOf(array, (Character) 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 Character) { int i = Chars.lastIndexOf(array, (Character) target, start, end); if (i >= 0) { return i - start; } } return -1; } @Override public Character set(int index, Character element) { checkElementIndex(index, size()); char oldValue = array[start + index]; // checkNotNull for GWT (do not optimize) array[start + index] = checkNotNull(element); return oldValue; } @Override public List<Character> subList(int fromIndex, int toIndex) { int size = size(); checkPositionIndexes(fromIndex, toIndex, size); if (fromIndex == toIndex) { return Collections.emptyList(); } return new CharArrayAsList(array, start + fromIndex, start + toIndex); } @Override public boolean equals(@Nullable Object object) { if (object == this) { return true; } if (object instanceof CharArrayAsList) { CharArrayAsList that = (CharArrayAsList) 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 + Chars.hashCode(array[i]); } return result; } @Override public String toString() { StringBuilder builder = new StringBuilder(size() * 3); builder.append('[').append(array[start]); for (int i = start + 1; i < end; i++) { builder.append(", ").append(array[i]); } return builder.append(']').toString(); } char[] toCharArray() { // Arrays.copyOfRange() is not available under GWT int size = size(); char[] result = new char[size]; System.arraycopy(array, start, result, 0, size); return result; } private static final long serialVersionUID = 0; } }