尽管您不希望使用循环，但我认为您应该使用循环。

String repeatString(String s, int repetitions)
{
    if(repetitions < 0) throw SomeException();

    else if(s == null) return null;

    StringBuilder stringBuilder = new StringBuilder(s.length() * repetitions);

    for(int i = 0; i < repetitions; i++)
        stringBuilder.append(s);

    return stringBuilder.toString();
}

你不使用for循环的理由并不充分。针对你的批评:

Whatever solution you use will almost certainly be longer than this. Using a pre-built function only tucks it under more covers. Someone reading your code will have to figure out what you're doing in that non-for-loop. Given that a for-loop is the idiomatic way to do this, it would be much easier to figure out if you did it with a for loop. Yes someone might add something clever, but by avoiding a for loop you are doing something clever. That's like shooting yourself in the foot intentionally to avoid shooting yourself in the foot by accident. Off-by-one errors are also mind-numbingly easy to catch with a single test. Given that you should be testing your code, an off-by-one error should be easy to fix and catch. And it's worth noting: the code above does not contain an off-by-one error. For loops are equally easy to get right. So don't reuse variables. That's not the for-loop's fault. Again, so does whatever solution you use. And as I noted before; a bug hunter will probably be expecting you to do this with a for loop, so they'll have an easier time finding it if you use a for loop.

在java-8中，你也可以使用Stream.generate。

import static java.util.stream.Collectors.joining;
...
String repeated = Stream.generate(() -> "abc").limit(3).collect(joining()); //"abcabcabc"

如果需要，你可以用一个简单的实用方法来包装它:

public static String repeat(String str, int times) {
   return Stream.generate(() -> str).limit(times).collect(joining());
}

我想要一个函数来为JDBC创建一个以逗号分隔的问号列表，然后找到了这篇文章。所以，我决定采用两个变体，看看哪个表现更好。在100万次迭代之后，普通的StringBuilder花了2秒(fun1)，而神秘的最优版本(fun2)花了30秒。又变得神秘有什么意义?

private static String fun1(int size) {
    StringBuilder sb = new StringBuilder(size * 2);
    for (int i = 0; i < size; i++) {
        sb.append(",?");
    }
    return sb.substring(1);
}

private static String fun2(int size) {
    return new String(new char[size]).replaceAll("\0", ",?").substring(1);
}

合并以供快速参考:

public class StringRepeat {

// Java 11 has built-in method - str.repeat(3);
// Apache - StringUtils.repeat(3);
// Google - Strings.repeat("",n);
// System.arraycopy

static String repeat_StringBuilderAppend(String str, int n) {

    if (str == null || str.isEmpty())
        return str;

    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < n; i++) {
        sb.append(str);
    }
    return sb.toString();
}

static String repeat_ArraysFill(String str, int n) {
    String[] strs = new String[n];
    Arrays.fill(strs, str);
    return Arrays.toString(strs).replaceAll("\\[|\\]|,| ", "");
}

static String repeat_Recursion(String str, int n) {
    if (n <= 0)
        return "";
    else
        return str + repeat_Recursion(str, n - 1);
}

static String repeat_format1(String str, int n) {
    return String.format(String.format("%%%ds", n), " ").replace(" ", str);
}

static String repeat_format2(String str, int n) {
    return new String(new char[n]).replace("\0", str);
}

static String repeat_format3(String str, int n) {
    return String.format("%0" + n + "d", 0).replace("0", str);
}

static String repeat_join(String str, int n) {
    return String.join("", Collections.nCopies(n, str));
}

static String repeat_stream(String str, int n) {
    return Stream.generate(() -> str).limit(n).collect(Collectors.joining());
}

public static void main(String[] args) {
    System.out.println(repeat_StringBuilderAppend("Mani", 3));
    System.out.println(repeat_ArraysFill("Mani", 3));
    System.out.println(repeat_Recursion("Mani", 3));
    System.out.println(repeat_format1("Mani", 3));
    System.out.println(repeat_format2("Mani", 3));
    System.out.println(repeat_format3("Mani", 3));
    System.out.println(repeat_join("Mani", 3));
    System.out.println(repeat_stream("Mani", 3));

}

}

简单明了的解决方案: 需要Java 8

Collections.nCopies( 3, "abc" ).stream().collect( Collectors.joining() );

Commons only StringUtils.repeat（）

用法:

String str = "abc";
String repeated = StringUtils.repeat(str, 3);

repeated.equals("abcabcabc");