Question

Which of the following creates the string of the numbers from 1 to 1000 most efficiently?

a. String s;
for (int i = 1; i <= 1000; i++)
s += i;
b. StringBuilder sb = new StringBuilder(10);
for (int i = 1; i <= 1000; i++)
(i);
String s = new String(sb);
c. StringBuilder sb = new StringBuilder(3000);
for (int i = 1; i <= 1000; i++)
(i);
String s = new String(sb);
d. All are equivalently efficient."

Answer 1

The most efficient method to create a string of numbers from 1 to 1000 is option C, utilizing a StringBuilder with an initial capacity of 3000 to avoid resizing overhead and improve performance.

Step-by-step explanation:

The most efficient method to create a string of the numbers from 1 to 1000 is option C.

It uses StringBuilder with an initial capacity of 3000. This is because StringBuilder is designed to be mutable and allows for efficient append operations without the overhead of creating a new string instance each time a number is added. The initial capacity is large enough to avoid frequent resizing of the internal buffer, which can be costly in terms of performance.

On the other hand, option A uses string concatenation, which is much less efficient since strings are immutable in Java. Each concatenation results in the creation of a new string object, leading to a significant performance cost, especially for a loop running 1000 times. Option B also uses StringBuilder, but the initial capacity of 10 is too small for our requirement and will trigger multiple resizings of the internal buffer as more numbers are appended, although it's still more efficient than option A.