JDK源码之lang.String(五)String类中的常用方法_string.lastindexof(int ch)-优快云博客

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本文详细解读了Java.lang.String类中lastIndexOf()方法的实现原理及用法，包括不同参数组合下如何查找字符串或字符最后一次出现的位置。

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java.lang.String类的lastIndexOf()方法

1.String类中的lastIndexOf(int ch)方法：

  public int lastIndexOf(int ch) {
        return lastIndexOf(ch, value.length - 1);
    }

2.String类中的lastIndexOf(int ch, int fromIndex)方法：

   public int lastIndexOf(int ch, int fromIndex) {
        if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) {
            // handle most cases here (ch is a BMP code point or a
            // negative value (invalid code point))
            final char[] value = this.value;
            int i = Math.min(fromIndex, value.length - 1);
            for (; i >= 0; i--) {
                if (value[i] == ch) {
                    return i;
                }
            }
            return -1;
        } else {
            return lastIndexOfSupplementary(ch, fromIndex);
        }
    }

3.String类中的lastIndexOfSupplementary(int ch, int fromIndex)方法：

 private int lastIndexOfSupplementary(int ch, int fromIndex) {
        if (Character.isValidCodePoint(ch)) {
            final char[] value = this.value;
            char hi = Character.highSurrogate(ch);
            char lo = Character.lowSurrogate(ch);
            int i = Math.min(fromIndex, value.length - 2);
            for (; i >= 0; i--) {
                if (value[i] == hi && value[i + 1] == lo) {
                    return i;
                }
            }
        }
        return -1;
    }

4.String类中的lastIndexOf(String str)方法：

    public int lastIndexOf(String str) {
        return lastIndexOf(str, value.length);
    }

5.String类中的lastIndexOf(String str, int fromIndex)方法：

    public int lastIndexOf(String str, int fromIndex) {
        return lastIndexOf(value, 0, value.length,
                str.value, 0, str.value.length, fromIndex);
    }

6.String类中的lastIndexOf(char[] source, int sourceOffset, int sourceCount, String target, int fromIndex)方法：

    static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
            String target, int fromIndex) {
        return lastIndexOf(source, sourceOffset, sourceCount,
                       target.value, 0, target.value.length,
                       fromIndex);
    }

7.String类中的lastIndexOf(char[] source, int sourceOffset, int sourceCount,char[] target, int targetOffset, int targetCount, int fromIndex)方法：

   static int lastIndexOf(char[] source, int sourceOffset, int sourceCount,
            char[] target, int targetOffset, int targetCount,
            int fromIndex) {
        /*
         * Check arguments; return immediately where possible. For
         * consistency, don't check for null str.
         */
        int rightIndex = sourceCount - targetCount;
        if (fromIndex < 0) {
            return -1;
        }
        if (fromIndex > rightIndex) {
            fromIndex = rightIndex;
        }
        /* Empty string always matches. */
        if (targetCount == 0) {
            return fromIndex;
        }

        int strLastIndex = targetOffset + targetCount - 1;
        char strLastChar = target[strLastIndex];
        int min = sourceOffset + targetCount - 1;
        int i = min + fromIndex;

    startSearchForLastChar:
        while (true) {
            while (i >= min && source[i] != strLastChar) {
                i--;
            }
            if (i < min) {
                return -1;
            }
            int j = i - 1;
            int start = j - (targetCount - 1);
            int k = strLastIndex - 1;

            while (j > start) {
                if (source[j--] != target[k--]) {
                    i--;
                    continue startSearchForLastChar;
                }
            }
            return start - sourceOffset + 1;
        }
    }