Java String index of matched char from end

//package com.demo2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        String str = "demo2s.com";
        char searchChar = 'a';
        System.out.println(lastIndexOf(str, searchChar));
    }/* w w w. jav a2  s  .c  o m*/

    /**
     * <p>Finds the last index within a String, handling <code>null</code>.
     * This method uses {@link String#lastIndexOf(int)}.</p>
     *
     * <p>A <code>null</code> or empty ("") String will return <code>-1</code>.</p>
     *
     * <pre>
     * lastIndexOf(null, *)         = -1
     * lastIndexOf("", *)           = -1
     * lastIndexOf("aabaabaa", 'a') = 7
     * lastIndexOf("aabaabaa", 'b') = 5
     * </pre>
     *
     * @param str  the String to check, may be null
     * @param searchChar  the character to find
     * @return the last index of the search character,
     *  -1 if no match or <code>null</code> string input
     * @since 2.0
     */
    public static int lastIndexOf(String str, char searchChar) {
        if (isEmpty(str)) {
            return -1;
        }
        return str.lastIndexOf(searchChar);
    }

    /**
     * <p>Finds the last index within a String from a start position,
     * handling <code>null</code>.
     * This method uses {@link String#lastIndexOf(int, int)}.</p>
     *
     * <p>A <code>null</code> or empty ("") String will return <code>-1</code>.
     * A negative start position returns <code>-1</code>.
     * A start position greater than the string length searches the whole string.</p>
     *
     * <pre>
     * lastIndexOf(null, *, *)          = -1
     * lastIndexOf("", *,  *)           = -1
     * lastIndexOf("aabaabaa", 'b', 8)  = 5
     * lastIndexOf("aabaabaa", 'b', 4)  = 2
     * lastIndexOf("aabaabaa", 'b', 0)  = -1
     * lastIndexOf("aabaabaa", 'b', 9)  = 5
     * lastIndexOf("aabaabaa", 'b', -1) = -1
     * lastIndexOf("aabaabaa", 'a', 0)  = 0
     * </pre>
     *
     * @param str  the String to check, may be null
     * @param searchChar  the character to find
     * @param startPos  the start position
     * @return the last index of the search character,
     *  -1 if no match or <code>null</code> string input
     * @since 2.0
     */
    public static int lastIndexOf(String str, char searchChar, int startPos) {
        if (isEmpty(str)) {
            return -1;
        }
        return str.lastIndexOf(searchChar, startPos);
    }

    /**
     * <p>Finds the last index within a String, handling <code>null</code>.
     * This method uses {@link String#lastIndexOf(String)}.</p>
     *
     * <p>A <code>null</code> String will return <code>-1</code>.</p>
     *
     * <pre>
     * lastIndexOf(null, *)          = -1
     * lastIndexOf(*, null)          = -1
     * lastIndexOf("", "")           = 0
     * lastIndexOf("aabaabaa", "a")  = 0
     * lastIndexOf("aabaabaa", "b")  = 2
     * lastIndexOf("aabaabaa", "ab") = 1
     * lastIndexOf("aabaabaa", "")   = 8
     * </pre>
     *
     * @param str  the String to check, may be null
     * @param searchStr  the String to find, may be null
     * @return the last index of the search String,
     *  -1 if no match or <code>null</code> string input
     * @since 2.0
     */
    public static int lastIndexOf(String str, String searchStr) {
        if (str == null || searchStr == null) {
            return -1;
        }
        return str.lastIndexOf(searchStr);
    }

    /**
     * <p>Finds the first index within a String, handling <code>null</code>.
     * This method uses {@link String#lastIndexOf(String, int)}.</p>
     *
     * <p>A <code>null</code> String will return <code>-1</code>.
     * A negative start position returns <code>-1</code>.
     * An empty ("") search String always matches unless the start position is negative.
     * A start position greater than the string length searches the whole string.</p>
     *
     * <pre>
     * lastIndexOf(null, *, *)          = -1
     * lastIndexOf(*, null, *)          = -1
     * lastIndexOf("aabaabaa", "a", 8)  = 7
     * lastIndexOf("aabaabaa", "b", 8)  = 5
     * lastIndexOf("aabaabaa", "ab", 8) = 4
     * lastIndexOf("aabaabaa", "b", 9)  = 5
     * lastIndexOf("aabaabaa", "b", -1) = -1
     * lastIndexOf("aabaabaa", "a", 0)  = 0
     * lastIndexOf("aabaabaa", "b", 0)  = -1
     * </pre>
     *
     * @param str  the String to check, may be null
     * @param searchStr  the String to find, may be null
     * @param startPos  the start position, negative treated as zero
     * @return the first index of the search String,
     *  -1 if no match or <code>null</code> string input
     * @since 2.0
     */
    public static int lastIndexOf(String str, String searchStr, int startPos) {
        if (str == null || searchStr == null) {
            return -1;
        }
        return str.lastIndexOf(searchStr, startPos);
    }

    /**
     * <p>Checks if a String is empty ("") or null.</p>
     *
     * <pre>
     * isEmpty(null)      = true
     * isEmpty("")        = true
     * isEmpty(" ")       = false
     * isEmpty("bob")     = false
     * isEmpty("  bob  ") = false
     * </pre>
     *
     * <p>NOTE: This method changed in Lang version 2.0.
     * It no longer trims the String.
     * That functionality is available in isBlank().</p>
     *
     * @param str  the String to check, may be null
     * @return <code>true</code> if the String is empty or null
     */
    public static boolean isEmpty(String str) {
        return str == null || str.length() == 0;
    }

}

/*
 * 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.
 */