Create a string with n characters

Question

Likely the shortest code using the String API, exclusively:

String space10 = new String(new char[10]).replace('\0', ' ');

System.out.println("[" + space10 + "]");
// prints "[          ]"

---

As a method, without directly instantiating char:

import java.nio.CharBuffer;

/**
 * Creates a string of spaces that is 'spaces' spaces long.
 *
 * @param spaces The number of spaces to add to the string.
 */
public String spaces( int spaces ) {
  return CharBuffer.allocate( spaces ).toString().replace( '\0', ' ' );
}

Invoke using:

System.out.printf( "[%s]%n", spaces( 10 ) );

I highly suggest not to write the loop by hand. You will do that over and over again during the course of your programming career. People reading your code - that includes you - always have to invest time, even if it are just some seconds, to digest the meaning of the loop.

Instead reuse one of the available libraries providing code that does just that like StringUtils.repeatfrom Apache Commons Lang:

StringUtils.repeat(' ', length);

That way you also do not have to bother about performance, thus all the gory details of StringBuilder, Compiler optimisations etc. are hidden. If the function would turn out as slow it would be a bug of the library.

With Java 11 it becomes even easier:

" ".repeat(length);

Hmm now that I think about it, maybe Arrays.fill:

char[] charArray = new char[length];
Arrays.fill(charArray, ' ');
String str = new String(charArray);

Of course, I assume that the fill method does the same thing as your code, so it will probably perform about the same, but at least this is fewer lines.

The for loop will be optimized by the compiler. In such cases like yours you don't need to care about optimization on your own. Trust the compiler.

BTW, if there is a way to create a string with n space characters, than it's coded the same way like you just did.

since Java 11:

" ".repeat(10);

---

since Java 8:

generate(() -> " ").limit(10).collect(joining());

where:

import static java.util.stream.Collectors.joining;
import static java.util.stream.Stream.generate;

In Java 8 you can use String.join:

String.join("", Collections.nCopies(n, s));