Java tutorial
/* * Copyright (c) 2000, 2018, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.lang; import java.util.NoSuchElementException; import java.util.Objects; import java.util.PrimitiveIterator; import java.util.Spliterator; import java.util.Spliterators; import java.util.function.IntConsumer; import java.util.stream.IntStream; import java.util.stream.StreamSupport; /** * A {@code CharSequence} is a readable sequence of {@code char} values. This * interface provides uniform, read-only access to many different kinds of * {@code char} sequences. * A {@code char} value represents a character in the <i>Basic * Multilingual Plane (BMP)</i> or a surrogate. Refer to <a * href="Character.html#unicode">Unicode Character Representation</a> for details. * * <p> This interface does not refine the general contracts of the {@link * java.lang.Object#equals(java.lang.Object) equals} and {@link * java.lang.Object#hashCode() hashCode} methods. The result of testing two objects * that implement {@code CharSequence} for equality is therefore, in general, undefined. * Each object may be implemented by a different class, and there * is no guarantee that each class will be capable of testing its instances * for equality with those of the other. It is therefore inappropriate to use * arbitrary {@code CharSequence} instances as elements in a set or as keys in * a map. </p> * * @author Mike McCloskey * @since 1.4 * @spec JSR-51 */ public interface CharSequence { /** * Returns the length of this character sequence. The length is the number * of 16-bit {@code char}s in the sequence. * * @return the number of {@code char}s in this sequence */ int length(); /** * Returns the {@code char} value at the specified index. An index ranges from zero * to {@code length() - 1}. The first {@code char} value of the sequence is at * index zero, the next at index one, and so on, as for array * indexing. * * <p>If the {@code char} value specified by the index is a * <a href="{@docRoot}/java.base/java/lang/Character.html#unicode">surrogate</a>, the surrogate * value is returned. * * @param index the index of the {@code char} value to be returned * * @return the specified {@code char} value * * @throws IndexOutOfBoundsException * if the {@code index} argument is negative or not less than * {@code length()} */ char charAt(int index); /** * Returns a {@code CharSequence} that is a subsequence of this sequence. * The subsequence starts with the {@code char} value at the specified index and * ends with the {@code char} value at index {@code end - 1}. The length * (in {@code char}s) of the * returned sequence is {@code end - start}, so if {@code start == end} * then an empty sequence is returned. * * @param start the start index, inclusive * @param end the end index, exclusive * * @return the specified subsequence * * @throws IndexOutOfBoundsException * if {@code start} or {@code end} are negative, * if {@code end} is greater than {@code length()}, * or if {@code start} is greater than {@code end} */ CharSequence subSequence(int start, int end); /** * Returns a string containing the characters in this sequence in the same * order as this sequence. The length of the string will be the length of * this sequence. * * @return a string consisting of exactly this sequence of characters */ public String toString(); /** * Returns a stream of {@code int} zero-extending the {@code char} values * from this sequence. Any char which maps to a <a * href="{@docRoot}/java.base/java/lang/Character.html#unicode">surrogate code * point</a> is passed through uninterpreted. * * <p>The stream binds to this sequence when the terminal stream operation * commences (specifically, for mutable sequences the spliterator for the * stream is <a href="../util/Spliterator.html#binding"><em>late-binding</em></a>). * If the sequence is modified during that operation then the result is * undefined. * * @return an IntStream of char values from this sequence * @since 1.8 */ public default IntStream chars() { class CharIterator implements PrimitiveIterator.OfInt { int cur = 0; public boolean hasNext() { return cur < length(); } public int nextInt() { if (hasNext()) { return charAt(cur++); } else { throw new NoSuchElementException(); } } @Override public void forEachRemaining(IntConsumer block) { for (; cur < length(); cur++) { block.accept(charAt(cur)); } } } return StreamSupport.intStream( () -> Spliterators.spliterator(new CharIterator(), length(), Spliterator.ORDERED), Spliterator.SUBSIZED | Spliterator.SIZED | Spliterator.ORDERED, false); } /** * Returns a stream of code point values from this sequence. Any surrogate * pairs encountered in the sequence are combined as if by {@linkplain * Character#toCodePoint Character.toCodePoint} and the result is passed * to the stream. Any other code units, including ordinary BMP characters, * unpaired surrogates, and undefined code units, are zero-extended to * {@code int} values which are then passed to the stream. * * <p>The stream binds to this sequence when the terminal stream operation * commences (specifically, for mutable sequences the spliterator for the * stream is <a href="../util/Spliterator.html#binding"><em>late-binding</em></a>). * If the sequence is modified during that operation then the result is * undefined. * * @return an IntStream of Unicode code points from this sequence * @since 1.8 */ public default IntStream codePoints() { class CodePointIterator implements PrimitiveIterator.OfInt { int cur = 0; @Override public void forEachRemaining(IntConsumer block) { final int length = length(); int i = cur; try { while (i < length) { char c1 = charAt(i++); if (!Character.isHighSurrogate(c1) || i >= length) { block.accept(c1); } else { char c2 = charAt(i); if (Character.isLowSurrogate(c2)) { i++; block.accept(Character.toCodePoint(c1, c2)); } else { block.accept(c1); } } } } finally { cur = i; } } public boolean hasNext() { return cur < length(); } public int nextInt() { final int length = length(); if (cur >= length) { throw new NoSuchElementException(); } char c1 = charAt(cur++); if (Character.isHighSurrogate(c1) && cur < length) { char c2 = charAt(cur); if (Character.isLowSurrogate(c2)) { cur++; return Character.toCodePoint(c1, c2); } } return c1; } } return StreamSupport.intStream( () -> Spliterators.spliteratorUnknownSize(new CodePointIterator(), Spliterator.ORDERED), Spliterator.ORDERED, false); } /** * Compares two {@code CharSequence} instances lexicographically. Returns a * negative value, zero, or a positive value if the first sequence is lexicographically * less than, equal to, or greater than the second, respectively. * * <p> * The lexicographical ordering of {@code CharSequence} is defined as follows. * Consider a {@code CharSequence} <i>cs</i> of length <i>len</i> to be a * sequence of char values, <i>cs[0]</i> to <i>cs[len-1]</i>. Suppose <i>k</i> * is the lowest index at which the corresponding char values from each sequence * differ. The lexicographic ordering of the sequences is determined by a numeric * comparison of the char values <i>cs1[k]</i> with <i>cs2[k]</i>. If there is * no such index <i>k</i>, the shorter sequence is considered lexicographically * less than the other. If the sequences have the same length, the sequences are * considered lexicographically equal. * * * @param cs1 the first {@code CharSequence} * @param cs2 the second {@code CharSequence} * * @return the value {@code 0} if the two {@code CharSequence} are equal; * a negative integer if the first {@code CharSequence} * is lexicographically less than the second; or a * positive integer if the first {@code CharSequence} is * lexicographically greater than the second. * * @since 11 */ @SuppressWarnings("unchecked") public static int compare(CharSequence cs1, CharSequence cs2) { if (Objects.requireNonNull(cs1) == Objects.requireNonNull(cs2)) { return 0; } if (cs1.getClass() == cs2.getClass() && cs1 instanceof Comparable) { return ((Comparable<Object>) cs1).compareTo(cs2); } for (int i = 0, len = Math.min(cs1.length(), cs2.length()); i < len; i++) { char a = cs1.charAt(i); char b = cs2.charAt(i); if (a != b) { return a - b; } } return cs1.length() - cs2.length(); } }