Strings.java
/*
* 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 static java.util.logging.Level.WARNING;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import java.util.logging.Logger;
import javax.annotation.CheckForNull;
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
@ElementTypesAreNonnullByDefault
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(@CheckForNull 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
*/
@CheckForNull
public static String emptyToNull(@CheckForNull 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(@CheckForNull 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));
}
/**
* Returns the given {@code template} string with each occurrence of {@code "%s"} replaced with
* the corresponding argument value from {@code args}; or, if the placeholder and argument counts
* do not match, returns a best-effort form of that string. Will not throw an exception under
* normal conditions.
*
* <p><b>Note:</b> For most string-formatting needs, use {@link String#format String.format},
* {@link java.io.PrintWriter#format PrintWriter.format}, and related methods. These support the
* full range of <a
* href="https://docs.oracle.com/javase/9/docs/api/java/util/Formatter.html#syntax">format
* specifiers</a>, and alert you to usage errors by throwing {@link
* java.util.IllegalFormatException}.
*
* <p>In certain cases, such as outputting debugging information or constructing a message to be
* used for another unchecked exception, an exception during string formatting would serve little
* purpose except to supplant the real information you were trying to provide. These are the cases
* this method is made for; it instead generates a best-effort string with all supplied argument
* values present. This method is also useful in environments such as GWT where {@code
* String.format} is not available. As an example, method implementations of the {@link
* Preconditions} class use this formatter, for both of the reasons just discussed.
*
* <p><b>Warning:</b> Only the exact two-character placeholder sequence {@code "%s"} is
* recognized.
*
* @param template a string containing zero or more {@code "%s"} placeholder sequences. {@code
* null} is treated as the four-character string {@code "null"}.
* @param args the arguments to be substituted into the message template. The first argument
* specified is substituted for the first occurrence of {@code "%s"} in the template, and so
* forth. A {@code null} argument is converted to the four-character string {@code "null"};
* non-null values are converted to strings using {@link Object#toString()}.
* @since 25.1
*/
// TODO(diamondm) consider using Arrays.toString() for array parameters
public static String lenientFormat(
@CheckForNull String template, @CheckForNull @Nullable Object... args) {
template = String.valueOf(template); // null -> "null"
if (args == null) {
args = new Object[] {"(Object[])null"};
} else {
for (int i = 0; i < args.length; i++) {
args[i] = lenientToString(args[i]);
}
}
// start substituting the arguments into the '%s' placeholders
StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
int templateStart = 0;
int i = 0;
while (i < args.length) {
int placeholderStart = template.indexOf("%s", templateStart);
if (placeholderStart == -1) {
break;
}
builder.append(template, templateStart, placeholderStart);
builder.append(args[i++]);
templateStart = placeholderStart + 2;
}
builder.append(template, templateStart, template.length());
// if we run out of placeholders, append the extra args in square braces
if (i < args.length) {
builder.append(" [");
builder.append(args[i++]);
while (i < args.length) {
builder.append(", ");
builder.append(args[i++]);
}
builder.append(']');
}
return builder.toString();
}
private static String lenientToString(@CheckForNull Object o) {
if (o == null) {
return "null";
}
try {
return o.toString();
} catch (Exception e) {
// Default toString() behavior - see Object.toString()
String objectToString =
o.getClass().getName() + '@' + Integer.toHexString(System.identityHashCode(o));
// Logger is created inline with fixed name to avoid forcing Proguard to create another class.
Logger.getLogger("com.google.common.base.Strings")
.log(WARNING, "Exception during lenientFormat for " + objectToString, e);
return "<" + objectToString + " threw " + e.getClass().getName() + ">";
}
}
}