如何从字符串中修剪空格？ [英] How to trim the whitespace from a string?

问题描述

我正在为J2ME应用程序编写这个函数，所以我没有一些更高级/现代的Java类可供我使用。我在这上面得到 java.lang.ArrayIndexOutOfBoundsException 。所以，显然要么它不喜欢我初始化 newChars 数组的方式，要么在调用 System时我没有做正确的事情。 arraycopy 。

I am writing this function for a J2ME application, so I don't have some of the more advanced / modern Java classes available to me. I am getting java.lang.ArrayIndexOutOfBoundsException on this. So, apparently either it doesn't like the way I've initialized the newChars array, or I'm not doing something correctly when calling System.arraycopy.

/*
 * remove any leading and trailing spaces
 */
public static String trim(String str) {
    char[] chars = str.toCharArray();
    int len = chars.length;
    // leading
    while ( (len > 0 ) && ( chars[0] == ' ' ) ) {
        char[] newChars = new char[] {}; // initialize empty array
        System.arraycopy(chars, 1, newChars, 0, len - 1);
        chars = newChars;
        len = chars.length;
    }
    // TODO: trailing
    return chars.toString();
}

推荐答案

修剪领先的简单方法和尾随空格是调用 String.trim（） 。如果你只想修剪前导和尾随空格（而不是所有前导和尾随空格），那么有一个名为 StringUtils.strip（String，String） 可以做到这一点;用作为第二个参数调用它。

The simple way to trim leading and trailing whitespace is to call String.trim(). If you just want to trim just leading and trailing spaces (rather than all leading and trailing whitespace), there is an Apache commons method called StringUtils.strip(String, String) that can do this; call it with " " as the 2nd argument.

你试过的代码有很多bug，从根本上来说效率低下。如果你真的想自己实现，那么你应该：

Your attempted code has a number of bugs, and is fundamentally inefficient. If you really want to implement this yourself, then you should:

1. 计算领先的空格字符


2. 计算尾随空格字符


3. 如果其中一个计数非零，则调用 String.substring（from，end）创建一个包含您要保留的字符的新字符串。

1. count the leading space characters
2. count the trailing space characters
3. if either count is non-zero, call String.substring(from, end) to create a new string containing the characters you want to keep.

此方法可避免复制任何字符 ¹ 。

This approach avoids copying any characters¹.

^{1 - 实际上，这取决于 String 。对于某些实现，将不进行复制，对于其他实现，则进行单个复制。但要么是你的方法的改进，需要至少2份，如果有任何要修剪的字符，则更多。}

^{1 - Actually, that depends on the implementation of String. For some implementations there will be no copying, for others a single copy is made. But either is an improvement on your approach, which entails a minimum of 2 copies, and more if there are any characters to trim.}

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