001/* 002 * Copyright (C) 2010 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.base; 016 017import static com.google.common.base.Preconditions.checkArgument; 018import static com.google.common.base.Preconditions.checkNotNull; 019import static java.lang.Math.min; 020import static java.util.logging.Level.WARNING; 021 022import com.google.common.annotations.GwtCompatible; 023import com.google.common.annotations.VisibleForTesting; 024import java.util.logging.Logger; 025import javax.annotation.CheckForNull; 026import org.checkerframework.checker.nullness.qual.Nullable; 027 028/** 029 * Static utility methods pertaining to {@code String} or {@code CharSequence} instances. 030 * 031 * @author Kevin Bourrillion 032 * @since 3.0 033 */ 034@GwtCompatible 035@ElementTypesAreNonnullByDefault 036public final class Strings { 037 private Strings() {} 038 039 /** 040 * Returns the given string if it is non-null; the empty string otherwise. 041 * 042 * @param string the string to test and possibly return 043 * @return {@code string} itself if it is non-null; {@code ""} if it is null 044 */ 045 public static String nullToEmpty(@CheckForNull String string) { 046 return Platform.nullToEmpty(string); 047 } 048 049 /** 050 * Returns the given string if it is nonempty; {@code null} otherwise. 051 * 052 * @param string the string to test and possibly return 053 * @return {@code string} itself if it is nonempty; {@code null} if it is empty or null 054 */ 055 @CheckForNull 056 public static String emptyToNull(@CheckForNull String string) { 057 return Platform.emptyToNull(string); 058 } 059 060 /** 061 * Returns {@code true} if the given string is null or is the empty string. 062 * 063 * <p>Consider normalizing your string references with {@link #nullToEmpty}. If you do, you can 064 * use {@link String#isEmpty()} instead of this method, and you won't need special null-safe forms 065 * of methods like {@link String#toUpperCase} either. Or, if you'd like to normalize "in the other 066 * direction," converting empty strings to {@code null}, you can use {@link #emptyToNull}. 067 * 068 * @param string a string reference to check 069 * @return {@code true} if the string is null or is the empty string 070 */ 071 public static boolean isNullOrEmpty(@CheckForNull String string) { 072 return Platform.stringIsNullOrEmpty(string); 073 } 074 075 /** 076 * Returns a string, of length at least {@code minLength}, consisting of {@code string} prepended 077 * with as many copies of {@code padChar} as are necessary to reach that length. For example, 078 * 079 * <ul> 080 * <li>{@code padStart("7", 3, '0')} returns {@code "007"} 081 * <li>{@code padStart("2010", 3, '0')} returns {@code "2010"} 082 * </ul> 083 * 084 * <p>See {@link java.util.Formatter} for a richer set of formatting capabilities. 085 * 086 * @param string the string which should appear at the end of the result 087 * @param minLength the minimum length the resulting string must have. Can be zero or negative, in 088 * which case the input string is always returned. 089 * @param padChar the character to insert at the beginning of the result until the minimum length 090 * is reached 091 * @return the padded string 092 */ 093 public static String padStart(String string, int minLength, char padChar) { 094 checkNotNull(string); // eager for GWT. 095 if (string.length() >= minLength) { 096 return string; 097 } 098 StringBuilder sb = new StringBuilder(minLength); 099 for (int i = string.length(); i < minLength; i++) { 100 sb.append(padChar); 101 } 102 sb.append(string); 103 return sb.toString(); 104 } 105 106 /** 107 * Returns a string, of length at least {@code minLength}, consisting of {@code string} appended 108 * with as many copies of {@code padChar} as are necessary to reach that length. For example, 109 * 110 * <ul> 111 * <li>{@code padEnd("4.", 5, '0')} returns {@code "4.000"} 112 * <li>{@code padEnd("2010", 3, '!')} returns {@code "2010"} 113 * </ul> 114 * 115 * <p>See {@link java.util.Formatter} for a richer set of formatting capabilities. 116 * 117 * @param string the string which should appear at the beginning of the result 118 * @param minLength the minimum length the resulting string must have. Can be zero or negative, in 119 * which case the input string is always returned. 120 * @param padChar the character to append to the end of the result until the minimum length is 121 * reached 122 * @return the padded string 123 */ 124 public static String padEnd(String string, int minLength, char padChar) { 125 checkNotNull(string); // eager for GWT. 126 if (string.length() >= minLength) { 127 return string; 128 } 129 StringBuilder sb = new StringBuilder(minLength); 130 sb.append(string); 131 for (int i = string.length(); i < minLength; i++) { 132 sb.append(padChar); 133 } 134 return sb.toString(); 135 } 136 137 /** 138 * Returns a string consisting of a specific number of concatenated copies of an input string. For 139 * example, {@code repeat("hey", 3)} returns the string {@code "heyheyhey"}. 140 * 141 * @param string any non-null string 142 * @param count the number of times to repeat it; a nonnegative integer 143 * @return a string containing {@code string} repeated {@code count} times (the empty string if 144 * {@code count} is zero) 145 * @throws IllegalArgumentException if {@code count} is negative 146 */ 147 public static String repeat(String string, int count) { 148 checkNotNull(string); // eager for GWT. 149 150 if (count <= 1) { 151 checkArgument(count >= 0, "invalid count: %s", count); 152 return (count == 0) ? "" : string; 153 } 154 155 // IF YOU MODIFY THE CODE HERE, you must update StringsRepeatBenchmark 156 final int len = string.length(); 157 final long longSize = (long) len * (long) count; 158 final int size = (int) longSize; 159 if (size != longSize) { 160 throw new ArrayIndexOutOfBoundsException("Required array size too large: " + longSize); 161 } 162 163 final char[] array = new char[size]; 164 string.getChars(0, len, array, 0); 165 int n; 166 for (n = len; n < size - n; n <<= 1) { 167 System.arraycopy(array, 0, array, n, n); 168 } 169 System.arraycopy(array, 0, array, n, size - n); 170 return new String(array); 171 } 172 173 /** 174 * Returns the longest string {@code prefix} such that {@code a.toString().startsWith(prefix) && 175 * b.toString().startsWith(prefix)}, taking care not to split surrogate pairs. If {@code a} and 176 * {@code b} have no common prefix, returns the empty string. 177 * 178 * @since 11.0 179 */ 180 public static String commonPrefix(CharSequence a, CharSequence b) { 181 checkNotNull(a); 182 checkNotNull(b); 183 184 int maxPrefixLength = min(a.length(), b.length()); 185 int p = 0; 186 while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) { 187 p++; 188 } 189 if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) { 190 p--; 191 } 192 return a.subSequence(0, p).toString(); 193 } 194 195 /** 196 * Returns the longest string {@code suffix} such that {@code a.toString().endsWith(suffix) && 197 * b.toString().endsWith(suffix)}, taking care not to split surrogate pairs. If {@code a} and 198 * {@code b} have no common suffix, returns the empty string. 199 * 200 * @since 11.0 201 */ 202 public static String commonSuffix(CharSequence a, CharSequence b) { 203 checkNotNull(a); 204 checkNotNull(b); 205 206 int maxSuffixLength = min(a.length(), b.length()); 207 int s = 0; 208 while (s < maxSuffixLength && a.charAt(a.length() - s - 1) == b.charAt(b.length() - s - 1)) { 209 s++; 210 } 211 if (validSurrogatePairAt(a, a.length() - s - 1) 212 || validSurrogatePairAt(b, b.length() - s - 1)) { 213 s--; 214 } 215 return a.subSequence(a.length() - s, a.length()).toString(); 216 } 217 218 /** 219 * True when a valid surrogate pair starts at the given {@code index} in the given {@code string}. 220 * Out-of-range indexes return false. 221 */ 222 @VisibleForTesting 223 static boolean validSurrogatePairAt(CharSequence string, int index) { 224 return index >= 0 225 && index <= (string.length() - 2) 226 && Character.isHighSurrogate(string.charAt(index)) 227 && Character.isLowSurrogate(string.charAt(index + 1)); 228 } 229 230 /** 231 * Returns the given {@code template} string with each occurrence of {@code "%s"} replaced with 232 * the corresponding argument value from {@code args}; or, if the placeholder and argument counts 233 * do not match, returns a best-effort form of that string. Will not throw an exception under 234 * normal conditions. 235 * 236 * <p><b>Note:</b> For most string-formatting needs, use {@link String#format String.format}, 237 * {@link java.io.PrintWriter#format PrintWriter.format}, and related methods. These support the 238 * full range of <a 239 * href="https://docs.oracle.com/javase/9/docs/api/java/util/Formatter.html#syntax">format 240 * specifiers</a>, and alert you to usage errors by throwing {@link 241 * java.util.IllegalFormatException}. 242 * 243 * <p>In certain cases, such as outputting debugging information or constructing a message to be 244 * used for another unchecked exception, an exception during string formatting would serve little 245 * purpose except to supplant the real information you were trying to provide. These are the cases 246 * this method is made for; it instead generates a best-effort string with all supplied argument 247 * values present. This method is also useful in environments such as GWT where {@code 248 * String.format} is not available. As an example, method implementations of the {@link 249 * Preconditions} class use this formatter, for both of the reasons just discussed. 250 * 251 * <p><b>Warning:</b> Only the exact two-character placeholder sequence {@code "%s"} is 252 * recognized. 253 * 254 * @param template a string containing zero or more {@code "%s"} placeholder sequences. {@code 255 * null} is treated as the four-character string {@code "null"}. 256 * @param args the arguments to be substituted into the message template. The first argument 257 * specified is substituted for the first occurrence of {@code "%s"} in the template, and so 258 * forth. A {@code null} argument is converted to the four-character string {@code "null"}; 259 * non-null values are converted to strings using {@link Object#toString()}. 260 * @since 25.1 261 */ 262 // TODO(diamondm) consider using Arrays.toString() for array parameters 263 public static String lenientFormat( 264 @CheckForNull String template, @CheckForNull @Nullable Object... args) { 265 template = String.valueOf(template); // null -> "null" 266 267 if (args == null) { 268 args = new Object[] {"(Object[])null"}; 269 } else { 270 for (int i = 0; i < args.length; i++) { 271 args[i] = lenientToString(args[i]); 272 } 273 } 274 275 // start substituting the arguments into the '%s' placeholders 276 StringBuilder builder = new StringBuilder(template.length() + 16 * args.length); 277 int templateStart = 0; 278 int i = 0; 279 while (i < args.length) { 280 int placeholderStart = template.indexOf("%s", templateStart); 281 if (placeholderStart == -1) { 282 break; 283 } 284 builder.append(template, templateStart, placeholderStart); 285 builder.append(args[i++]); 286 templateStart = placeholderStart + 2; 287 } 288 builder.append(template, templateStart, template.length()); 289 290 // if we run out of placeholders, append the extra args in square braces 291 if (i < args.length) { 292 builder.append(" ["); 293 builder.append(args[i++]); 294 while (i < args.length) { 295 builder.append(", "); 296 builder.append(args[i++]); 297 } 298 builder.append(']'); 299 } 300 301 return builder.toString(); 302 } 303 304 private static String lenientToString(@CheckForNull Object o) { 305 if (o == null) { 306 return "null"; 307 } 308 try { 309 return o.toString(); 310 } catch (Exception e) { 311 // Default toString() behavior - see Object.toString() 312 String objectToString = 313 o.getClass().getName() + '@' + Integer.toHexString(System.identityHashCode(o)); 314 // Logger is created inline with fixed name to avoid forcing Proguard to create another class. 315 Logger.getLogger("com.google.common.base.Strings") 316 .log(WARNING, "Exception during lenientFormat for " + objectToString, e); 317 return "<" + objectToString + " threw " + e.getClass().getName() + ">"; 318 } 319 } 320}