Java中的标记

在翻看String源码的时候发现了以下代码:

   / *
     *
     * @param locale use the case transformation rules for this locale
     * @return the {@code String}, converted to lowercase.
     * @see     java.lang.String#toLowerCase()
     * @see     java.lang.String#toUpperCase()
     * @see     java.lang.String#toUpperCase(Locale)
     * @since   1.1
     */
    public String toLowerCase(Locale locale) {
        if (locale == null) {
            throw new NullPointerException();
        }

        int firstUpper;
        final int len = value.length;

中间这一部分代码:用到了Java标记 这里的scan就是一个跳转标记 通常在包含循环体的代码中 设定跳转标记 在continue或者break后添加标记 跳转到标记处开始执行 这样做的目的是跳过本次循环或跳出循环体 这里是当

• if (c != Character.toLowerCase(c))
  满足时候结束for循环

/* Now check if there are any characters that need to be changed. */
scan: {
for (firstUpper = 0 ; firstUpper < len; ) {
char c = value[firstUpper];
if ((c >= Character.MIN_HIGH_SURROGATE)
&& (c <= Character.MAX_HIGH_SURROGATE)) {
int supplChar = codePointAt(firstUpper);
if (supplChar != Character.toLowerCase(supplChar)) {
break scan;
}
firstUpper += Character.charCount(supplChar);
} else {
if (c != Character.toLowerCase(c)) {
break scan;

                }
                   firstUpper++;
               }
           }
           return this;
       }

       char[] result = new char[len];
       int resultOffset = 0;  /* result may grow, so i+resultOffset
                               * is the write location in result */

       /* Just copy the first few lowerCase characters. */
       System.arraycopy(value, 0, result, 0, firstUpper);

       String lang = locale.getLanguage();
       boolean localeDependent =
               (lang == "tr" || lang == "az" || lang == "lt");
       char[] lowerCharArray;
       int lowerChar;
       int srcChar;
       int srcCount;
       for (int i = firstUpper; i < len; i += srcCount) {
           srcChar = (int)value[i];
           if ((char)srcChar >= Character.MIN_HIGH_SURROGATE
                   && (char)srcChar <= Character.MAX_HIGH_SURROGATE) {
               srcChar = codePointAt(i);
               srcCount = Character.charCount(srcChar);
           } else {
               srcCount = 1;
           }
           if (localeDependent ||
               srcChar == '\u03A3' || // GREEK CAPITAL LETTER SIGMA
               srcChar == '\u0130') { // LATIN CAPITAL LETTER I WITH DOT ABOVE
               lowerChar = ConditionalSpecialCasing.toLowerCaseEx(this, i, locale);
           } else {
               lowerChar = Character.toLowerCase(srcChar);
           }
           if ((lowerChar == Character.ERROR)
                   || (lowerChar >= Character.MIN_SUPPLEMENTARY_CODE_POINT)) {
               if (lowerChar == Character.ERROR) {
                   lowerCharArray =
                           ConditionalSpecialCasing.toLowerCaseCharArray(this, i, locale);
               } else if (srcCount == 2) {
                   resultOffset += Character.toChars(lowerChar, result, i + resultOffset) - srcCount;
                   continue;
               } else {
                   lowerCharArray = Character.toChars(lowerChar);
               }

               /* Grow result if needed */
               int mapLen = lowerCharArray.length;
               if (mapLen > srcCount) {
                   char[] result2 = new char[result.length + mapLen - srcCount];
                   System.arraycopy(result, 0, result2, 0, i + resultOffset);
                   result = result2;
               }
               for (int x = 0; x < mapLen; ++x) {
                   result[i + resultOffset + x] = lowerCharArray[x];
               }
               resultOffset += (mapLen - srcCount);
           } else {
               result[i + resultOffset] = (char)lowerChar;
           }
       }
       return new String(result, 0, len + resultOffset);
   }

• 小试牛刀:

/**
 * 这个例子主要介绍的是java中跳转标记的使用
 * 
 * 起因是在String.toLowercase(Locale locale)中 发现一个scan:标记
 * 
 * @author Administrator
 *
 */
public class ScanFlag {

    /**
     * 计算[0-length]区间内奇数的和
     * 
     * @param length
     * @return
     */
    public static int computeOdds(int length) {

        int sum = 0;
        odd: for (int i = 0; i <=length; i++) {
            if (i % 2 == 0)
                continue odd;
            sum += i;
        }
        return sum;
    }

    /**
     * 计算[0-length]区间内偶数的和
     * 
     * @param length
     * @return
     */
    public static int computeEvens(int length) {
        int sum = 0;
        even: for (int i = 0; i <=length; i++) {
            if (i % 2 != 0)
                continue even;
            sum += i;
        }
        return sum;
    }

    public static void main(String[] args) {
        
        int odds=computeOdds(10);
        int evens=computeEvens(10);
        
        System.out.println("10以内偶数的和是:"+odds);
        System.out.println("10以内奇数的和是:"+evens);
    }
}

执行结果如下：

10以内偶数的和是:25
10以内奇数的和是:30