guava/src/com/google/common/base/Strings.java - platform/external/guava - Git at Google

 /*
  * 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
    */
   public static @Nullable 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));
   }
 }
	/*
	* 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
	*/
	public static @Nullable 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));
	}
	}