public boolean contentEquals(CharSequence cs) {
        if (count != cs.length())
            return false;
        // Argument is a StringBuffer, StringBuilder
        if (cs instanceof AbstractStringBuilder) {
            char v1[] = value;
            char v2[] = ((AbstractStringBuilder)cs).getValue();
            int i = offset;
            int j = 0;
            int n = count;
            while (n-- != 0) {
                if (v1[i++] != v2[j++])
                    return false;
            }
///////////// SINCE ALL CHARACTERS ARE EQUAL, WHY NOT RETURN TRUE HERE?
        }
        // Argument is a String
        if (cs.equals(this))
            return true;
        // Argument is a generic CharSequence
        char v1[] = value;
        int i = offset;
        int j = 0;
        int n = count;
        while (n-- != 0) {
            if (v1[i++] != cs.charAt(j++))
                return false;
        }
        return true;
    }

------解决方案--------------------
比如，"abc".contentEquals(new StringBuilder("abc"))将比较两次

------解决方案--------------------
String中间另外一个问题（也在7中修正），虽然谈不上性能影响，但是很傻:
Java code
    private static class CaseInsensitiveComparator
                         implements Comparator<String>, java.io.Serializable {
    // use serialVersionUID from JDK 1.2.2 for interoperability
    private static final long serialVersionUID = 8575799808933029326L;

        public int compare(String s1, String s2) {
            int n1=s1.length(), n2=s2.length();
            for (int i1=0, i2=0; i1<n1 && i2<n2; i1++, i2++) {
                char c1 = s1.charAt(i1);
                char c2 = s2.charAt(i2);
                if (c1 != c2) {
                    c1 = Character.toUpperCase(c1);
                    c2 = Character.toUpperCase(c2);
                    if (c1 != c2) {
                        c1 = Character.toLowerCase(c1);
                        c2 = Character.toLowerCase(c2);
                        if (c1 != c2) {
                            return c1 - c2;
                        }
                    }
                }
            }
            return n1 - n2;
        }
    }

------解决方案--------------------
类a在sun的jvm可能很慢，但在ibm j9或者jrockit上可能很快，这个说不好的，再说有运行时优化，会编译成本地代码，不同的jvm优化算法也是大不相同，自然效率也就不一样

------解决方案--------------------
我知道有几个：