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      1 /*
      2  * Copyright (C) 2016 The Android Open Source Project
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  *   http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.calculator2;
     18 
     19 /**
     20  * Some helpful methods operating on strings.
     21  */
     22 
     23 public class StringUtils {
     24 
     25     /**
     26      * Return a string with n copies of c.
     27      */
     28     public static String repeat(char c, int n) {
     29         final StringBuilder result = new StringBuilder();
     30         for (int i = 0; i < n; ++i) {
     31             result.append(c);
     32         }
     33         return result.toString();
     34     }
     35 
     36     /**
     37      * Return a copy of the supplied string with commas added every three digits.
     38      * The substring indicated by the supplied range is assumed to contain only
     39      * a whole number, with no decimal point.
     40      * Inserting a digit separator every 3 digits appears to be
     41      * at least somewhat acceptable, though not necessarily preferred, everywhere.
     42      * The grouping separator in the result is NOT localized.
     43      */
     44     public static String addCommas(String s, int begin, int end) {
     45         // Resist the temptation to use Java's NumberFormat, which converts to long or double
     46         // and hence doesn't handle very large numbers.
     47         StringBuilder result = new StringBuilder();
     48         int current = begin;
     49         while (current < end && (s.charAt(current) == '-' || s.charAt(current) == ' ')) {
     50             ++current;
     51         }
     52         result.append(s, begin, current);
     53         while (current < end) {
     54             result.append(s.charAt(current));
     55             ++current;
     56             if ((end - current) % 3 == 0 && end != current) {
     57                 result.append(',');
     58             }
     59         }
     60         return result.toString();
     61     }
     62 
     63     /**
     64      * Ignoring all occurrences of c in both strings, check whether old is a prefix of new.
     65      * If so, return the remaining subsequence of whole. If not, return null.
     66      */
     67     public static CharSequence getExtensionIgnoring(CharSequence whole, CharSequence prefix,
     68             char c) {
     69         int wIndex = 0;
     70         int pIndex = 0;
     71         final int wLen = whole.length();
     72         final int pLen = prefix.length();
     73         while (true) {
     74             while (pIndex < pLen && prefix.charAt(pIndex) == c) {
     75                 ++pIndex;
     76             }
     77             while (wIndex < wLen && whole.charAt(wIndex) == c) {
     78                 ++wIndex;
     79             }
     80             if (pIndex == pLen) {
     81                 break;
     82             }
     83             if (wIndex == wLen || whole.charAt(wIndex) != prefix.charAt(pIndex) ) {
     84                 return null;
     85             }
     86             ++pIndex;
     87             ++wIndex;
     88         }
     89         while (wIndex < wLen && whole.charAt(wIndex) == c) {
     90             ++wIndex;
     91         }
     92         return whole.subSequence(wIndex, wLen);
     93     }
     94 }
     95