重复字符串的简单方法

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.

当前回答

使用Dollar就像输入一样简单:

@Test
public void repeatString() {
    String string = "abc";
    assertThat($(string).repeat(3).toString(), is("abcabcabc"));
}

PS:重复工作也为数组，列表，集等

2010-02-01 16:01:28

其他回答

基于fortran的答案，这是一个使用StringBuilder的递归版本:

public static void repeat(StringBuilder stringBuilder, String s, int times) {
    if (times > 0) {
        repeat(stringBuilder.append(s), s, times - 1);
    }
}

public static String repeat(String s, int times) {
    StringBuilder stringBuilder = new StringBuilder(s.length() * times);
    repeat(stringBuilder, s, times);
    return stringBuilder.toString();
}

2009-08-06 03:57:28

不是最短的，但(我认为)最快的方法是使用StringBuilder:

 /**
   * Repeat a String as many times you need.
   *
   * @param i - Number of Repeating the String.
   * @param s - The String wich you want repeated.
   * @return The string n - times.
   */
  public static String repeate(int i, String s) {
    StringBuilder sb = new StringBuilder();
    for (int j = 0; j < i; j++)
      sb.append(s);
    return sb.toString();
  }

2017-10-12 12:58:47

这是最新的Stringutils.java

    public static String repeat(String str, int repeat) {
    // Performance tuned for 2.0 (JDK1.4)

    if (str == null) {
        return null;
    }
    if (repeat <= 0) {
        return EMPTY;
    }
    int inputLength = str.length();
    if (repeat == 1 || inputLength == 0) {
        return str;
    }
    if (inputLength == 1 && repeat <= PAD_LIMIT) {
        return repeat(str.charAt(0), repeat);
    }

    int outputLength = inputLength * repeat;
    switch (inputLength) {
        case 1 :
            return repeat(str.charAt(0), repeat);
        case 2 :
            char ch0 = str.charAt(0);
            char ch1 = str.charAt(1);
            char[] output2 = new char[outputLength];
            for (int i = repeat * 2 - 2; i >= 0; i--, i--) {
                output2[i] = ch0;
                output2[i + 1] = ch1;
            }
            return new String(output2);
        default :
            StringBuilder buf = new StringBuilder(outputLength);
            for (int i = 0; i < repeat; i++) {
                buf.append(str);
            }
            return buf.toString();
    }
    }

它甚至不需要这么大，可以做成这样，可以复制和粘贴到项目中的实用程序类中。

    public static String repeat(String str, int num) {
    int len = num * str.length();
    StringBuilder sb = new StringBuilder(len);
    for (int i = 0; i < times; i++) {
        sb.append(str);
    }
    return sb.toString();
    }

所以e5，我认为最好的方法是简单地使用上面提到的代码，或者这里的任何答案。但是如果它是一个小项目，Commons lang就太大了

2011-08-10 23:55:05

如果你使用的是Java <= 7，这是最“简洁”的:

// create a string made up of n copies of string s
String.format("%0" + n + "d", 0).replace("0", s);

在Java 8及以上版本中，有一种更易读的方式:

// create a string made up of n copies of string s
String.join("", Collections.nCopies(n, s));

最后，对于Java 11及以上版本，有一个专门用于此目的的新的repeat (int count)方法(链接)

"abc".repeat(12);

或者，如果您的项目使用java库，则有更多的选项。

对于Apache Commons:

StringUtils.repeat("abc", 12);

谷歌番石榴:

Strings.repeat("abc", 12);

2011-07-28 11:05:56

如果你只知道输出字符串的长度(它可能不能被输入字符串的长度整除)，那么使用这个方法:

static String repeat(String s, int length) {
    return s.length() >= length ? s.substring(0, length) : repeat(s + s, length);
}

使用演示:

for (int i = 0; i < 50; i++)
    System.out.println(repeat("_/‾\\", i));

不要使用空s，长度为> 0，因为在这种情况下不可能得到想要的结果。

2020-05-18 19:16:54

重复字符串的简单方法

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