-
Notifications
You must be signed in to change notification settings - Fork 10.9k
/
Strings.java
223 lines (205 loc) · 8.1 KB
/
Strings.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
/*
* Copyright (C) 2010 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.base;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Static utility methods pertaining to {@code String} or {@code CharSequence} instances.
*
* @author Kevin Bourrillion
* @since 3.0
*/
@GwtCompatible
public final class Strings {
private Strings() {}
/**
* Returns the given string if it is non-null; the empty string otherwise.
*
* @param string the string to test and possibly return
* @return {@code string} itself if it is non-null; {@code ""} if it is null
*/
public static String nullToEmpty(@Nullable String string) {
return Platform.nullToEmpty(string);
}
/**
* Returns the given string if it is nonempty; {@code null} otherwise.
*
* @param string the string to test and possibly return
* @return {@code string} itself if it is nonempty; {@code null} if it is empty or null
*/
public static @Nullable String emptyToNull(@Nullable String string) {
return Platform.emptyToNull(string);
}
/**
* Returns {@code true} if the given string is null or is the empty string.
*
* <p>Consider normalizing your string references with {@link #nullToEmpty}. If you do, you can
* use {@link String#isEmpty()} instead of this method, and you won't need special null-safe forms
* of methods like {@link String#toUpperCase} either. Or, if you'd like to normalize "in the other
* direction," converting empty strings to {@code null}, you can use {@link #emptyToNull}.
*
* @param string a string reference to check
* @return {@code true} if the string is null or is the empty string
*/
public static boolean isNullOrEmpty(@Nullable String string) {
return Platform.stringIsNullOrEmpty(string);
}
/**
* Returns a string, of length at least {@code minLength}, consisting of {@code string} prepended
* with as many copies of {@code padChar} as are necessary to reach that length. For example,
*
* <ul>
* <li>{@code padStart("7", 3, '0')} returns {@code "007"}
* <li>{@code padStart("2010", 3, '0')} returns {@code "2010"}
* </ul>
*
* <p>See {@link java.util.Formatter} for a richer set of formatting capabilities.
*
* @param string the string which should appear at the end of the result
* @param minLength the minimum length the resulting string must have. Can be zero or negative, in
* which case the input string is always returned.
* @param padChar the character to insert at the beginning of the result until the minimum length
* is reached
* @return the padded string
*/
public static String padStart(String string, int minLength, char padChar) {
checkNotNull(string); // eager for GWT.
if (string.length() >= minLength) {
return string;
}
StringBuilder sb = new StringBuilder(minLength);
for (int i = string.length(); i < minLength; i++) {
sb.append(padChar);
}
sb.append(string);
return sb.toString();
}
/**
* Returns a string, of length at least {@code minLength}, consisting of {@code string} appended
* with as many copies of {@code padChar} as are necessary to reach that length. For example,
*
* <ul>
* <li>{@code padEnd("4.", 5, '0')} returns {@code "4.000"}
* <li>{@code padEnd("2010", 3, '!')} returns {@code "2010"}
* </ul>
*
* <p>See {@link java.util.Formatter} for a richer set of formatting capabilities.
*
* @param string the string which should appear at the beginning of the result
* @param minLength the minimum length the resulting string must have. Can be zero or negative, in
* which case the input string is always returned.
* @param padChar the character to append to the end of the result until the minimum length is
* reached
* @return the padded string
*/
public static String padEnd(String string, int minLength, char padChar) {
checkNotNull(string); // eager for GWT.
if (string.length() >= minLength) {
return string;
}
StringBuilder sb = new StringBuilder(minLength);
sb.append(string);
for (int i = string.length(); i < minLength; i++) {
sb.append(padChar);
}
return sb.toString();
}
/**
* Returns a string consisting of a specific number of concatenated copies of an input string. For
* example, {@code repeat("hey", 3)} returns the string {@code "heyheyhey"}.
*
* @param string any non-null string
* @param count the number of times to repeat it; a nonnegative integer
* @return a string containing {@code string} repeated {@code count} times (the empty string if
* {@code count} is zero)
* @throws IllegalArgumentException if {@code count} is negative
*/
public static String repeat(String string, int count) {
checkNotNull(string); // eager for GWT.
if (count <= 1) {
checkArgument(count >= 0, "invalid count: %s", count);
return (count == 0) ? "" : string;
}
// IF YOU MODIFY THE CODE HERE, you must update StringsRepeatBenchmark
final int len = string.length();
final long longSize = (long) len * (long) count;
final int size = (int) longSize;
if (size != longSize) {
throw new ArrayIndexOutOfBoundsException("Required array size too large: " + longSize);
}
final char[] array = new char[size];
string.getChars(0, len, array, 0);
int n;
for (n = len; n < size - n; n <<= 1) {
System.arraycopy(array, 0, array, n, n);
}
System.arraycopy(array, 0, array, n, size - n);
return new String(array);
}
/**
* Returns the longest string {@code prefix} such that {@code a.toString().startsWith(prefix) &&
* b.toString().startsWith(prefix)}, taking care not to split surrogate pairs. If {@code a} and
* {@code b} have no common prefix, returns the empty string.
*
* @since 11.0
*/
public static String commonPrefix(CharSequence a, CharSequence b) {
checkNotNull(a);
checkNotNull(b);
int maxPrefixLength = Math.min(a.length(), b.length());
int p = 0;
while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) {
p++;
}
if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) {
p--;
}
return a.subSequence(0, p).toString();
}
/**
* Returns the longest string {@code suffix} such that {@code a.toString().endsWith(suffix) &&
* b.toString().endsWith(suffix)}, taking care not to split surrogate pairs. If {@code a} and
* {@code b} have no common suffix, returns the empty string.
*
* @since 11.0
*/
public static String commonSuffix(CharSequence a, CharSequence b) {
checkNotNull(a);
checkNotNull(b);
int maxSuffixLength = Math.min(a.length(), b.length());
int s = 0;
while (s < maxSuffixLength && a.charAt(a.length() - s - 1) == b.charAt(b.length() - s - 1)) {
s++;
}
if (validSurrogatePairAt(a, a.length() - s - 1)
|| validSurrogatePairAt(b, b.length() - s - 1)) {
s--;
}
return a.subSequence(a.length() - s, a.length()).toString();
}
/**
* True when a valid surrogate pair starts at the given {@code index} in the given {@code string}.
* Out-of-range indexes return false.
*/
@VisibleForTesting
static boolean validSurrogatePairAt(CharSequence string, int index) {
return index >= 0
&& index <= (string.length() - 2)
&& Character.isHighSurrogate(string.charAt(index))
&& Character.isLowSurrogate(string.charAt(index + 1));
}
}