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

repeated = str + str + str;

有时候简单是最好的。每个阅读代码的人都可以看到发生了什么。

编译器会在幕后用StringBuilder为你做一些奇特的事情。

2014-10-09 13:23:49

其他回答

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?

2013-04-02 21:20:59

这里有一种只使用标准String函数而没有显式循环的方法:

// create a string made up of  n  copies of  s
repeated = String.format(String.format("%%%ds", n), " ").replace(" ",s);

2009-08-22 18:05:06

简单的循环

public static String repeat(String string, int times) {
    StringBuilder out = new StringBuilder();
    while (times-- > 0) {
        out.append(string);
    }
    return out.toString();
}

2013-06-25 11:49:26

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

只使用JRE类(System.arraycopy)并尽量减少临时对象的数量，你可以这样写:

public static String repeat(String toRepeat, int times) {
    if (toRepeat == null) {
        toRepeat = "";
    }

    if (times < 0) {
        times = 0;
    }

    final int length = toRepeat.length();
    final int total = length * times;
    final char[] src = toRepeat.toCharArray();
    char[] dst = new char[total];

    for (int i = 0; i < total; i += length) {
        System.arraycopy(src, 0, dst, i, length);
    }

    return String.copyValueOf(dst);
}

EDIT

如果没有循环，你可以尝试:

public static String repeat2(String toRepeat, int times) {
    if (toRepeat == null) {
        toRepeat = "";
    }

    if (times < 0) {
        times = 0;
    }

    String[] copies = new String[times];
    Arrays.fill(copies, toRepeat);
    return Arrays.toString(copies).
              replace("[", "").
              replace("]", "").
              replaceAll(", ", "");
}

编辑2

使用Collections甚至更短:

public static String repeat3(String toRepeat, int times) {
    return Collections.nCopies(times, toRepeat).
           toString().
           replace("[", "").
           replace("]", "").
           replaceAll(", ", "");
}

然而，我仍然喜欢第一个版本。

2009-08-05 19:53:10

重复字符串的简单方法

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