StringBuilder length() 方法的时间复杂度

Question

What is the time complexity of length() method from StringBuilder class?

String str = "hello";
StringBuilder sb = new StringBuilder(str);

System.out.println(sb.length()); // should print 5

My assumption is O(n) where n is number of characters in the string, similar to length() from String class.

Answer 1

This is a member variable in StringBuilder class:

/**
 * The count is the number of characters used.
 */
int count;

And this is the code of length() :

/**
 * Returns the length (character count).
 *
 * @return  the length of the sequence of characters currently
 *          represented by this object
 */
@Override
public int length() {
    return count;
}

What do you think?