| /* |
| * Copyright (c) 2013, 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.util; |
| |
| /** |
| * {@code StringJoiner} is used to construct a sequence of characters separated |
| * by a delimiter and optionally starting with a supplied prefix |
| * and ending with a supplied suffix. |
| * <p> |
| * Prior to adding something to the {@code StringJoiner}, its |
| * {@code sj.toString()} method will, by default, return {@code prefix + suffix}. |
| * However, if the {@code setEmptyValue} method is called, the {@code emptyValue} |
| * supplied will be returned instead. This can be used, for example, when |
| * creating a string using set notation to indicate an empty set, i.e. |
| * <code>"{}"</code>, where the {@code prefix} is <code>"{"</code>, the |
| * {@code suffix} is <code>"}"</code> and nothing has been added to the |
| * {@code StringJoiner}. |
| * |
| * @apiNote |
| * <p>The String {@code "[George:Sally:Fred]"} may be constructed as follows: |
| * |
| * <pre> {@code |
| * StringJoiner sj = new StringJoiner(":", "[", "]"); |
| * sj.add("George").add("Sally").add("Fred"); |
| * String desiredString = sj.toString(); |
| * }</pre> |
| * <p> |
| * A {@code StringJoiner} may be employed to create formatted output from a |
| * {@link java.util.stream.Stream} using |
| * {@link java.util.stream.Collectors#joining(CharSequence)}. For example: |
| * |
| * <pre> {@code |
| * List<Integer> numbers = Arrays.asList(1, 2, 3, 4); |
| * String commaSeparatedNumbers = numbers.stream() |
| * .map(i -> i.toString()) |
| * .collect(Collectors.joining(", ")); |
| * }</pre> |
| * |
| * @see java.util.stream.Collectors#joining(CharSequence) |
| * @see java.util.stream.Collectors#joining(CharSequence, CharSequence, CharSequence) |
| * @since 1.8 |
| */ |
| public final class StringJoiner { |
| private final String prefix; |
| private final String delimiter; |
| private final String suffix; |
| |
| /* |
| * StringBuilder value -- at any time, the characters constructed from the |
| * prefix, the added element separated by the delimiter, but without the |
| * suffix, so that we can more easily add elements without having to jigger |
| * the suffix each time. |
| */ |
| private StringBuilder value; |
| |
| /* |
| * By default, the string consisting of prefix+suffix, returned by |
| * toString(), or properties of value, when no elements have yet been added, |
| * i.e. when it is empty. This may be overridden by the user to be some |
| * other value including the empty String. |
| */ |
| private String emptyValue; |
| |
| /** |
| * Constructs a {@code StringJoiner} with no characters in it, with no |
| * {@code prefix} or {@code suffix}, and a copy of the supplied |
| * {@code delimiter}. |
| * If no characters are added to the {@code StringJoiner} and methods |
| * accessing the value of it are invoked, it will not return a |
| * {@code prefix} or {@code suffix} (or properties thereof) in the result, |
| * unless {@code setEmptyValue} has first been called. |
| * |
| * @param delimiter the sequence of characters to be used between each |
| * element added to the {@code StringJoiner} value |
| * @throws NullPointerException if {@code delimiter} is {@code null} |
| */ |
| public StringJoiner(CharSequence delimiter) { |
| this(delimiter, "", ""); |
| } |
| |
| /** |
| * Constructs a {@code StringJoiner} with no characters in it using copies |
| * of the supplied {@code prefix}, {@code delimiter} and {@code suffix}. |
| * If no characters are added to the {@code StringJoiner} and methods |
| * accessing the string value of it are invoked, it will return the |
| * {@code prefix + suffix} (or properties thereof) in the result, unless |
| * {@code setEmptyValue} has first been called. |
| * |
| * @param delimiter the sequence of characters to be used between each |
| * element added to the {@code StringJoiner} |
| * @param prefix the sequence of characters to be used at the beginning |
| * @param suffix the sequence of characters to be used at the end |
| * @throws NullPointerException if {@code prefix}, {@code delimiter}, or |
| * {@code suffix} is {@code null} |
| */ |
| public StringJoiner(CharSequence delimiter, |
| CharSequence prefix, |
| CharSequence suffix) { |
| Objects.requireNonNull(prefix, "The prefix must not be null"); |
| Objects.requireNonNull(delimiter, "The delimiter must not be null"); |
| Objects.requireNonNull(suffix, "The suffix must not be null"); |
| // make defensive copies of arguments |
| this.prefix = prefix.toString(); |
| this.delimiter = delimiter.toString(); |
| this.suffix = suffix.toString(); |
| this.emptyValue = this.prefix + this.suffix; |
| } |
| |
| /** |
| * Sets the sequence of characters to be used when determining the string |
| * representation of this {@code StringJoiner} and no elements have been |
| * added yet, that is, when it is empty. A copy of the {@code emptyValue} |
| * parameter is made for this purpose. Note that once an add method has been |
| * called, the {@code StringJoiner} is no longer considered empty, even if |
| * the element(s) added correspond to the empty {@code String}. |
| * |
| * @param emptyValue the characters to return as the value of an empty |
| * {@code StringJoiner} |
| * @return this {@code StringJoiner} itself so the calls may be chained |
| * @throws NullPointerException when the {@code emptyValue} parameter is |
| * {@code null} |
| */ |
| public StringJoiner setEmptyValue(CharSequence emptyValue) { |
| this.emptyValue = Objects.requireNonNull(emptyValue, |
| "The empty value must not be null").toString(); |
| return this; |
| } |
| |
| /** |
| * Returns the current value, consisting of the {@code prefix}, the values |
| * added so far separated by the {@code delimiter}, and the {@code suffix}, |
| * unless no elements have been added in which case, the |
| * {@code prefix + suffix} or the {@code emptyValue} characters are returned |
| * |
| * @return the string representation of this {@code StringJoiner} |
| */ |
| @Override |
| public String toString() { |
| if (value == null) { |
| return emptyValue; |
| } else { |
| if (suffix.equals("")) { |
| return value.toString(); |
| } else { |
| int initialLength = value.length(); |
| String result = value.append(suffix).toString(); |
| // reset value to pre-append initialLength |
| value.setLength(initialLength); |
| return result; |
| } |
| } |
| } |
| |
| /** |
| * Adds a copy of the given {@code CharSequence} value as the next |
| * element of the {@code StringJoiner} value. If {@code newElement} is |
| * {@code null}, then {@code "null"} is added. |
| * |
| * @param newElement The element to add |
| * @return a reference to this {@code StringJoiner} |
| */ |
| public StringJoiner add(CharSequence newElement) { |
| prepareBuilder().append(newElement); |
| return this; |
| } |
| |
| /** |
| * Adds the contents of the given {@code StringJoiner} without prefix and |
| * suffix as the next element if it is non-empty. If the given {@code |
| * StringJoiner} is empty, the call has no effect. |
| * |
| * <p>A {@code StringJoiner} is empty if {@link #add(CharSequence) add()} |
| * has never been called, and if {@code merge()} has never been called |
| * with a non-empty {@code StringJoiner} argument. |
| * |
| * <p>If the other {@code StringJoiner} is using a different delimiter, |
| * then elements from the other {@code StringJoiner} are concatenated with |
| * that delimiter and the result is appended to this {@code StringJoiner} |
| * as a single element. |
| * |
| * @param other The {@code StringJoiner} whose contents should be merged |
| * into this one |
| * @throws NullPointerException if the other {@code StringJoiner} is null |
| * @return This {@code StringJoiner} |
| */ |
| public StringJoiner merge(StringJoiner other) { |
| Objects.requireNonNull(other); |
| if (other.value != null) { |
| final int length = other.value.length(); |
| // lock the length so that we can seize the data to be appended |
| // before initiate copying to avoid interference, especially when |
| // merge 'this' |
| StringBuilder builder = prepareBuilder(); |
| builder.append(other.value, other.prefix.length(), length); |
| } |
| return this; |
| } |
| |
| private StringBuilder prepareBuilder() { |
| if (value != null) { |
| value.append(delimiter); |
| } else { |
| value = new StringBuilder().append(prefix); |
| } |
| return value; |
| } |
| |
| /** |
| * Returns the length of the {@code String} representation |
| * of this {@code StringJoiner}. Note that if |
| * no add methods have been called, then the length of the {@code String} |
| * representation (either {@code prefix + suffix} or {@code emptyValue}) |
| * will be returned. The value should be equivalent to |
| * {@code toString().length()}. |
| * |
| * @return the length of the current value of {@code StringJoiner} |
| */ |
| public int length() { |
| // Remember that we never actually append the suffix unless we return |
| // the full (present) value or some sub-string or length of it, so that |
| // we can add on more if we need to. |
| return (value != null ? value.length() + suffix.length() : |
| emptyValue.length()); |
| } |
| } |
