/*
* 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 java.util.Formatter;
import javax.annotation.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 (string == null) ? "" : 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
*/
@Nullable
public static String emptyToNull(@Nullable String string) {
return isNullOrEmpty(string) ? null : 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 string == null || string.length() == 0; // string.isEmpty() in Java 6
}
/**
* 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 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 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));
}
}