我正在寻找一个简单的公共方法或操作符，允许我重复一些字符串n次。我知道我可以使用for循环来写这个，但我希望在必要时避免for循环，并且应该在某个地方存在一个简单的直接方法。
String str = "abc";
String repeated = str.repeat(3);
repeated.equals("abcabcabc");
相关:
重复字符串javascript
通过重复给定次数的另一个字符串创建NSString
编辑
当它们不是完全必要的时候，我尽量避免使用for循环，因为:
They add to the number of lines of code even if they are tucked away in another function.
Someone reading my code has to figure out what I am doing in that for loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever".
Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix".
They are very often easy to get wrong. For loops involving indexes tend to generate off by one bugs.
For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs.
For loops increase the number of places a bug hunter has to look.
我很喜欢这个问题。有很多知识和风格。所以我不能没有展示我的摇滚就离开;)
{
String string = repeat("1234567890", 4);
System.out.println(string);
System.out.println("=======");
repeatWithoutCopySample(string, 100000);
System.out.println(string);// This take time, try it without printing
System.out.println(string.length());
}
/**
* The core of the task.
*/
@SuppressWarnings("AssignmentToMethodParameter")
public static char[] repeat(char[] sample, int times) {
char[] r = new char[sample.length * times];
while (--times > -1) {
System.arraycopy(sample, 0, r, times * sample.length, sample.length);
}
return r;
}
/**
* Java classic style.
*/
public static String repeat(String sample, int times) {
return new String(repeat(sample.toCharArray(), times));
}
/**
* Java extreme memory style.
*/
@SuppressWarnings("UseSpecificCatch")
public static void repeatWithoutCopySample(String sample, int times) {
try {
Field valueStringField = String.class.getDeclaredField("value");
valueStringField.setAccessible(true);
valueStringField.set(sample, repeat((char[]) valueStringField.get(sample), times));
} catch (Exception ex) {
throw new RuntimeException(ex);
}
}
你喜欢吗?
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));
}
}
字符串:重复
". ".repeat(7) // Seven period-with-space pairs: . . . . . . .
Java 11中的新方法是String::repeat，它完全符合你的要求:
String str = "abc";
String repeated = str.repeat(3);
repeated.equals("abcabcabc");
它的Javadoc说:
/**
* Returns a string whose value is the concatenation of this
* string repeated {@code count} times.
* <p>
* If this string is empty or count is zero then the empty
* string is returned.
*
* @param count number of times to repeat
*
* @return A string composed of this string repeated
* {@code count} times or the empty string if this
* string is empty or count is zero
*
* @throws IllegalArgumentException if the {@code count} is
* negative.
*
* @since 11
*/
