src/com/android/calculator2/StringUtils.java

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * 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.android.calculator2;

/**
 * Some helpful methods operating on strings.
 */

public class StringUtils {

    /**
     * Return a string with n copies of c.
     */
    public static String repeat(char c, int n) {
        final StringBuilder result = new StringBuilder();
        for (int i = 0; i < n; ++i) {
            result.append(c);
        }
        return result.toString();
    }

    /**
     * Return a copy of the supplied string with commas added every three digits.
     * The substring indicated by the supplied range is assumed to contain only
     * a whole number, with no decimal point.
     * Inserting a digit separator every 3 digits appears to be
     * at least somewhat acceptable, though not necessarily preferred, everywhere.
     * The grouping separator in the result is NOT localized.
     */
    public static String addCommas(String s, int begin, int end) {
        // Resist the temptation to use Java's NumberFormat, which converts to long or double
        // and hence doesn't handle very large numbers.
        StringBuilder result = new StringBuilder();
        int current = begin;
        while (current < end && (s.charAt(current) == '-' || s.charAt(current) == ' ')) {
            ++current;
        }
        result.append(s, begin, current);
        while (current < end) {
            result.append(s.charAt(current));
            ++current;
            if ((end - current) % 3 == 0 && end != current) {
                result.append(',');
            }
        }
        return result.toString();
    }

    /**
     * Ignoring all occurrences of c in both strings, check whether old is a prefix of new.
     * If so, return the remaining subsequence of whole. If not, return null.
     */
    public static CharSequence getExtensionIgnoring(CharSequence whole, CharSequence prefix,
            char c) {
        int wIndex = 0;
        int pIndex = 0;
        final int wLen = whole.length();
        final int pLen = prefix.length();
        while (true) {
            while (pIndex < pLen && prefix.charAt(pIndex) == c) {
                ++pIndex;
            }
            while (wIndex < wLen && whole.charAt(wIndex) == c) {
                ++wIndex;
            }
            if (pIndex == pLen) {
                break;
            }
            if (wIndex == wLen || whole.charAt(wIndex) != prefix.charAt(pIndex) ) {
                return null;
            }
            ++pIndex;
            ++wIndex;
        }
        while (wIndex < wLen && whole.charAt(wIndex) == c) {
            ++wIndex;
        }
        return whole.subSequence(wIndex, wLen);
    }
}