Java從字符串中替換精確的子字符串

Question

我有以下字符串：

String str = "6,20,9,10,19,11,5,3,1,2";

並且我想將確切的字符串,2或1,替換為空字符串，避免將子字符串,20或11,包含在替換中。

我有這個代碼：

// assuming that substr = ",2" or "1,"

if(str.startsWith(substr+",")){
    str = str.replace("^"+substr+",$","");
}               
else if(str.contains(","+substr+",")){
    str = str.replace("^"+substr+",$","");
}   
else if(str.endsWith(","+substr)){
    str = str.replace("^,"+substr+"$","");
}

但似乎我對正則表達式錯了。 我應該使用哪個正則表達式來解決它？

Answer 1

我的回答是：“你想要實現什么？”

如果你試圖過濾我會去String.split(",") ，然后過濾字符串數組中生成的項目。 最終我會加入它們（如果你不受運行時限制）。

像（ 未經測試 ）的東西：

String[] splits = myString.split(",");
// ... manipulate splits (filter into a list if you want...)
StringUtils.join(splits, ", "); // possibly replace with array from filtered list

• 拆分可以由篩選列表的toArray替換

以你的方式解決它可能會很棘手。 當您嘗試匹配項目時，您將無法匹配其鄰居。 您需要做的是匹配聚合。

這只是一個開始（ 未經測試 ，基於此 ）：

    List<String> matches = new ArrayList<String>();
    Matcher m = Pattern.compile("(^[12],|,[12],|[12]$)").matcher("1,6,20,9,10,19,11,5,3,1,2");
    if (m.find()) {
        do {
            System.out.println("Matched "+m.group());
            matches.add(m.group());
        } while (m.find(m.start()+1));
    }

    for (String match : matches){
        System.out.println(match);
    }

您可以嘗試兩種方式運行時間，也可以稍后擴展我的答案:-)

Answer 2

我相信問題是“如何從列表中刪除值”，但只有確切的值（例如2不是12,13而不是413），並縮短列表，即刪除前面或后面的逗號，如果有的話，但不是兩個。

簡答：

String x = Pattern.quote(textToRemove);
Pattern p = Pattern.compile("^"+x+"$|^"+x+",|,"+x+"$|,"+x+"(?=,)");
String output = p.matcher(input).replaceAll(""); // or replaceFirst

例子：

Input:       "6,20,9,10,19,101,5,3,1,2"
Remove "2":  "6,20,9,10,19,101,5,3,1"   -- last value, don't remove 20
Remove "20": "6,9,10,19,101,5,3,1,2"    -- middle value
Remove "1":  "6,20,9,10,19,101,5,3,2"   -- don't remove 10, 19, or 101
Remove "10": "6,20,9,19,101,5,3,1,2"    -- don't remove 101
Remove "6":  "20,9,10,19,101,5,3,1,2"   -- first value
Remove "77": "6,20,9,10,19,101,5,3,1,2" -- nothing removed

Input:       "6"
Remove "6":  ""                         -- only value

碼：

private static void test(String input, String textToRemove) {
    String rmv = Pattern.quote(textToRemove);
    Pattern p = Pattern.compile("^" + rmv + "$" +     // matches only value
                               "|^" + rmv + "," +     // matches first value + ','
                               "|," + rmv + "$" +     // matches ',' + last value
                               "|," + rmv + "(?=,)"); // matches ',' + middle value (+ ',')
    String output = p.matcher(input).replaceAll(""); // or replaceFirst
    System.out.printf("Remove %-4s from %-26s: %s%n",
                      '"' + textToRemove + '"',
                      '"' + input + '"',
                      '"' + output + '"');
}

測試：

public static void main(String[] args) throws Exception {
    //
    test("6,20,9,10,19,101,5,3,1,2", "2" );
    test("6,20,9,10,19,101,5,3,1,2", "20");
    test("6,20,9,10,19,101,5,3,1,2", "1" );
    test("6,20,9,10,19,101,5,3,1,2", "10");
    test("6,20,9,10,19,101,5,3,1,2", "6" );
    test("6,20,9,10,19,101,5,3,1,2", "77");
    test("6"                       , "6" );
}

輸出：

Remove "2"  from "6,20,9,10,19,101,5,3,1,2": "6,20,9,10,19,101,5,3,1"
Remove "20" from "6,20,9,10,19,101,5,3,1,2": "6,9,10,19,101,5,3,1,2"
Remove "1"  from "6,20,9,10,19,101,5,3,1,2": "6,20,9,10,19,101,5,3,2"
Remove "10" from "6,20,9,10,19,101,5,3,1,2": "6,20,9,19,101,5,3,1,2"
Remove "6"  from "6,20,9,10,19,101,5,3,1,2": "20,9,10,19,101,5,3,1,2"
Remove "77" from "6,20,9,10,19,101,5,3,1,2": "6,20,9,10,19,101,5,3,1,2"
Remove "6"  from "6"                       : ""