String.replace() 不替换所有出现

Question

I have a very long string which looks similar to this.

355,356,357,358,359,360,361,382,363,364,365,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,368,369,313,370,371,372,373,374,375,376,377,378,379,380,381,382,382,382,382,382,382,383,384,385,380,381,382,382,382,382,382,386,387,388,389,380,381,382,382,382,382,382,382,390,391,380,381,382,382,382,382,382,392,393,394,395,396,397,398,399,....

When I tried using the following code to remove the number 382 from the string.

String str = "355,356,357,358,359,360,361,382,363,364,365,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,368,369,313,370,371,372,373,374,375,376,377,378,379,380,381,382,382,382,382,382,382,383,384,385,380,381,382,382,382,382,382,386,387,388,389,380,381,382,382,382,382,382,382,390,391,380,381,382,382,382,382,382,392,393,394,395,396,397,398,399,...."
str = str.replace(",382,", ",");

But it seems that not all occurrences are being replaced. The string which originally had above 3000 occurrences still was left with about 630 occurrences after replacing.

Is the capability of String.replace() limited? If so, is there a possible way of achieving what I need?

Answer 1

I think the issue is your first argument to replace() , in particular the comma (,) before and after 382. If you have "382,382,383", you will only match the inner ",382," and leave the initial one behind. Try:

str.replace("382,", "");

Although this will fail to match "382" at the very end as it does not have a comma after it.

A full solution might entail two method calls thus:

str = str.replace("382", "");  // Remove all instances of 382
str.replaceAll(",,+", ",");    // Compress all duplicates, triplicates, etc. of commas

This combines the two approaches:

str.replaceAll("382,?", "");  // Remove 382 and an optional comma after it. 

Note: both of the last two approaches leave a trailing comma if 382 is at the end.

Answer 2

You need to replace the trailing comma as well (if one exists, which it won't if last in the list):

str = str.replaceAll("\\b382,?", "");

Note \\b word boundary to prevent matching "-,1382,-" .

The above will convert:

382,111,382,1382,222,382

to:

111,1382,222

Answer 3

尝试这个

str = str.replaceAll(",382,", ",");

Answer 4

Firstly, remove the preceding comma in your matching string. Then, remove duplicated commas by replacing commas with a single comma using java regular expression.

 String input = "355,356,357,358,359,360,361,382,363,364,365,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,360,361,363,366,368,369,313,370,371,372,373,374,375,376,377,378,379,380,381,382,382,382,382,382,382,383,384,385,380,381,382,382,382,382,382,386,387,388,389,380,381,382,382,382,382,382,382,390,391,380,381,382,382,382,382,382,392,393,394,395,396,397,398,399";
    String result = input.replace("382,", ","); // remove the preceding comma
    String result2 = result.replaceAll("[,]+", ","); // replace duplicate commas

    System.out.println(result2);

Answer 5

As dave already said, the problem is that your pattern overlaps. In the string "...,382,382,..." there are two occurrences of ",382," :

"...,382,382,..."
    -----         first occurrence
        -----     second occurrence

These two occurrences overlap at the comma, and thus Java can only replace one of them. When finding occurrences, it does not see yet what you replace the pattern with, and thus it doesn't see that new occurrence of ",382," is generated when replacing the first occurrence is replaced by the comma.

If your data is known not to contain numbers with more than 3 digits, then you might do:

str.replace("382,", "");

and then handle occurrences at the end as a special case. But if your data can contain big numbers, then "...,1382,..." will be replaced by "...,1,..." which probably is not what you want.

Here are two solutions that do not have the above problem:

First, simply repeat the replacement until no changes occur anymore:

String oldString = str;
str = str.replace(",382,", ",");
while (!str.equals(oldString)) {
    oldString = str;
    str = str.replace(",382,", ",");
}

After that, you will have to handle possible occurrences at the end of the string.

Second, if you have Java 8, you can do a little more work yourself and use Java streams:

str = Arrays.stream(str.split(","))
    .filter(s -> !s.equals("382"))
    .collect(Collectors.joining(","));

This first splits the string at ",", then filters out all strings which are equal to "382", and then concatenates the remaining strings again with "," in between.

(Both code snippets are untested.)

Answer 6

Traditional way:

    String str = ",abc,null,null,0,0,7,8,9,10,11,12,13,14";
    String newStr = "", word = "";
    for (int i=0; i<str.length(); i++) {
        if (str.charAt(i) == ',') {
            if (word.equals("null") || word.equals("0"))
                word = "";
            newStr += word+",";
            word = "";
        } else {
            word += str.charAt(i);
            if (i == str.length()-1)
                newStr += word;
        }
    }
    System.out.println(newStr);

Output: ,abc,,,,,7,8,9,10,11,12,13,14