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Some thing about the useful tools of the JDK 1.8.
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package com.github.andyshao.util;

/**
 * 
 * Title: some usefu tools of java.lang.String

 * Descript:

 * Copyright: Copryright(c) Apr 28, 2014

 * Encoding:UNIX UTF-8
 * 
 * @author Andy.Shao
 *
 */
public final class StringTools {
    /**
     * 
     * @param str a string which should be flipped
     * @return A string which has flipped.
     */
    public static String flipString(String str){
    	return new String(ArrayTools.flipArray(str.toCharArray()));
    }
    
    /**
     * 
     * @param str a string which should be tested.
     * @return if the str is null or "", return the true
     */
    public static boolean isEmptyOrNull(String str) {
        return str == null || str.isEmpty();
    }

    /**
     * more efficient

     * replace the string
     * 
     * @param str the string which will be process
     * @param padding the right words will be inputed
     * @param index the right words will be inputed
     * @param length the length of string which should be replaced
     * @return the end of the string
     */
    static String replace(String str , String padding , int index , int length) {
        String result;
        if (index == -1) {
            result = str;
        } else {
            if (index == 0) {
                result = padding + str.substring(length);
            } else if (index + 1 >= str.length()) {
                result = str.substring(0 , index) + padding;
            } else {
                result = str.substring(0 , index) + padding + str.substring(index + length);
            }
        }

        return result;
    }

    /**
     * more efficient

     * replace all of the key words
     * 
     * @param str the string which will be process
     * @param key the key words will be instead
     * @param padding the right words will be inputed
     * @return the end of the string
     */
    public static String replaceAll(String str , String key , String padding) {
        while (str.indexOf(key) != -1) {
            str = StringTools.replaceFirst(str , key , padding);
        }
        return str;
    }

    /**
     * more efficient

     * only replace the first time occur
     * 
     * @param str the string which will be process
     * @param key the key words will be insted
     * @param padding the right words will be inputed
     * @return the end of the string
     */
    public static String replaceFirst(String str , String key , String padding) {
        return StringTools.replace(str , padding , str.indexOf(key) , key.length());
    }

    /**
     * more efficient

     * only replace the last time occur
     * 
     * @param str the string which will be process
     * @param key the key words will be insted
     * @param padding the right words will be inputed
     * @return the end of the string
     */
    public static String replaceLast(String str , String key , String padding) {
        return StringTools.replace(str , padding , str.lastIndexOf(key) , key.length());
    }

    /**
     * more efficient

     * split the string by separator
     * 
     * @param str the string which will be process
     * @param separator the str will be splited by it
     * @return the end of string
     */
    public static String[] split(String str , String separator) {
        String[] result = new String[0];
        for (int index ; (index = str.indexOf(separator)) != -1 ;) {
            result = ArrayTools.mergeArray(String[].class , result , new String[] {
                str.substring(0 , index)
            });
            str = str.substring(index + separator.length());
        }
        if (str.length() != 0) {
            result = ArrayTools.mergeArray(String[].class , result , new String[] {
                str
            });
        }

        return result;
    }

    private StringTools() {
        throw new AssertionError("Not allowed to instance " + StringTools.class.getName());
    }
}