FastAsyncWorldEdit/src/main/java/com/sk89q/util/StringUtil.java

274 Zeilen
9.3 KiB
Java

// $Id$
/*
* Copyright (C) 2010 sk89q <http://www.sk89q.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
package com.sk89q.util;
import java.util.Collection;
/**
* String utilities.
*
* @author sk89q
*/
public class StringUtil {
/**
* Trim a string if it is longer than a certain length.
*
* @param str
* @param len
* @return
*/
public static String trimLength(String str, int len) {
if (str.length() > len) {
return str.substring(0, len);
}
return str;
}
/**
* Join an array of strings into a string.
*
* @param str
* @param delimiter
* @param initialIndex
* @return
*/
public static String joinString(String[] str, String delimiter,
int initialIndex) {
if (str.length == 0) {
return "";
}
StringBuilder buffer = new StringBuilder(str[initialIndex]);
for (int i = initialIndex + 1; i < str.length; ++i) {
buffer.append(delimiter).append(str[i]);
}
return buffer.toString();
}
/**
* Join an array of strings into a string.
*
* @param str
* @param delimiter
* @param initialIndex
* @param quote
* @return
*/
public static String joinQuotedString(String[] str, String delimiter,
int initialIndex, String quote) {
if (str.length == 0) {
return "";
}
StringBuilder buffer = new StringBuilder();
buffer.append(quote);
buffer.append(str[initialIndex]);
buffer.append(quote);
for (int i = initialIndex + 1; i < str.length; ++i) {
buffer.append(delimiter).append(quote).append(str[i]).append(quote);
}
return buffer.toString();
}
/**
* Join an array of strings into a string.
*
* @param str
* @param delimiter
* @return
*/
public static String joinString(String[] str, String delimiter) {
return joinString(str, delimiter, 0);
}
/**
* Join an array of strings into a string.
*
* @param str
* @param delimiter
* @param initialIndex
* @return
*/
public static String joinString(Object[] str, String delimiter,
int initialIndex) {
if (str.length == 0) {
return "";
}
StringBuilder buffer = new StringBuilder(str[initialIndex].toString());
for (int i = initialIndex + 1; i < str.length; ++i) {
buffer.append(delimiter).append(str[i].toString());
}
return buffer.toString();
}
/**
* Join an array of strings into a string.
*
* @param str
* @param delimiter
* @param initialIndex
* @return
*/
public static String joinString(int[] str, String delimiter,
int initialIndex) {
if (str.length == 0) {
return "";
}
StringBuilder buffer = new StringBuilder(Integer.toString(str[initialIndex]));
for (int i = initialIndex + 1; i < str.length; ++i) {
buffer.append(delimiter).append(Integer.toString(str[i]));
}
return buffer.toString();
}
/**
* Join an list of strings into a string.
*
* @param str
* @param delimiter
* @param initialIndex
* @return
*/
public static String joinString(Collection<?> str, String delimiter,
int initialIndex) {
if (str.size() == 0) {
return "";
}
StringBuilder buffer = new StringBuilder();
int i = 0;
for (Object o : str) {
if (i >= initialIndex) {
if (i > 0) {
buffer.append(delimiter);
}
buffer.append(o.toString());
}
++i;
}
return buffer.toString();
}
/**
* <p>Find the Levenshtein distance between two Strings.</p>
*
* <p>This is the number of changes needed to change one String into
* another, where each change is a single character modification (deletion,
* insertion or substitution).</p>
*
* <p>The previous implementation of the Levenshtein distance algorithm
* was from <a href="http://www.merriampark.com/ld.htm">http://www.merriampark.com/ld.htm</a></p>
*
* <p>Chas Emerick has written an implementation in Java, which avoids an OutOfMemoryError
* which can occur when my Java implementation is used with very large strings.<br>
* This implementation of the Levenshtein distance algorithm
* is from <a href="http://www.merriampark.com/ldjava.htm">http://www.merriampark.com/ldjava.htm</a></p>
*
* <pre>
* StringUtil.getLevenshteinDistance(null, *) = IllegalArgumentException
* StringUtil.getLevenshteinDistance(*, null) = IllegalArgumentException
* StringUtil.getLevenshteinDistance("","") = 0
* StringUtil.getLevenshteinDistance("","a") = 1
* StringUtil.getLevenshteinDistance("aaapppp", "") = 7
* StringUtil.getLevenshteinDistance("frog", "fog") = 1
* StringUtil.getLevenshteinDistance("fly", "ant") = 3
* StringUtil.getLevenshteinDistance("elephant", "hippo") = 7
* StringUtil.getLevenshteinDistance("hippo", "elephant") = 7
* StringUtil.getLevenshteinDistance("hippo", "zzzzzzzz") = 8
* StringUtil.getLevenshteinDistance("hello", "hallo") = 1
* </pre>
*
* @param s the first String, must not be null
* @param t the second String, must not be null
* @return result distance
* @throws IllegalArgumentException if either String input <code>null</code>
*/
public static int getLevenshteinDistance(String s, String t) {
if (s == null || t == null) {
throw new IllegalArgumentException("Strings must not be null");
}
/*
* The difference between this impl. and the previous is that, rather
* than creating and retaining a matrix of size s.length()+1 by
* t.length()+1, we maintain two single-dimensional arrays of length
* s.length()+1. The first, d, is the 'current working' distance array
* that maintains the newest distance cost counts as we iterate through
* the characters of String s. Each time we increment the index of
* String t we are comparing, d is copied to p, the second int[]. Doing
* so allows us to retain the previous cost counts as required by the
* algorithm (taking the minimum of the cost count to the left, up one,
* and diagonally up and to the left of the current cost count being
* calculated). (Note that the arrays aren't really copied anymore, just
* switched...this is clearly much better than cloning an array or doing
* a System.arraycopy() each time through the outer loop.)
*
* Effectively, the difference between the two implementations is this
* one does not cause an out of memory condition when calculating the LD
* over two very large strings.
*/
int n = s.length(); // length of s
int m = t.length(); // length of t
if (n == 0) {
return m;
} else if (m == 0) {
return n;
}
int p[] = new int[n + 1]; // 'previous' cost array, horizontally
int d[] = new int[n + 1]; // cost array, horizontally
int _d[]; // placeholder to assist in swapping p and d
// indexes into strings s and t
int i; // iterates through s
int j; // iterates through t
char t_j; // jth character of t
int cost; // cost
for (i = 0; i <= n; ++i) {
p[i] = i;
}
for (j = 1; j <= m; ++j) {
t_j = t.charAt(j - 1);
d[0] = j;
for (i = 1; i <= n; ++i) {
cost = s.charAt(i - 1) == t_j ? 0 : 1;
// minimum of cell to the left+1, to the top+1, diagonally left
// and up +cost
d[i] = Math.min(Math.min(d[i - 1] + 1, p[i] + 1), p[i - 1]
+ cost);
}
// copy current distance counts to 'previous row' distance counts
_d = p;
p = d;
d = _d;
}
// our last action in the above loop was to switch d and p, so p now
// actually has the most recent cost counts
return p[n];
}
}