使用 StringBuilder 时从 last 中删除逗号

Question

我有以下 Java 程序，但我不想在最后一个元素之后分配“,”，怎么办？

String range = "400-450";
        Integer startRange = null;
        Integer endRange = null;
        StringTokenizer st = new StringTokenizer(range,"-");  
        while(st.hasMoreTokens()) { 
            startRange = Integer.parseInt(st.nextToken()); 
            endRange= Integer.parseInt(st.nextToken()); 
        } 
        StringBuilder sb = new StringBuilder();
        for (int i = startRange; i <= endRange; i++) {
            sb.append(i).append(",");
        }
        System.out.println(sb);

输出应该是 400,401,402,403,404,405,406,407,408,409,410,411,412,413,414,415,416,417,418,419,420,421,422,423,424,425,426,427,428,429,430,431,432,433,434,435,436,437,438,439,440,441,442,443,444,445,446,447,448,449,450 --> 最后没有逗号

Answer 1

对于 Java 8，您可以切换到新的 class StringJoiner，它正是为 目的而添加的:

    StringJoiner sb = new StringJoiner(",");
    for (int i = startRange; i <= endRange; i++) {
        sb.add(String.valueOf(i));
    }
    System.out.println(sb.toString());

手动执行，我建议在项目之前添加逗号 然后使用 substring(1):

for (int i = startRange; i <= endRange; i++) { sb.append(",").append(i); } //Check for empty before! System.out.println(sb.substring(1));

Answer 2

让最后一个附加逗号的循环在到达最后一个元素之前停止：

String range = "400-450";
        Integer startRange = null;
        Integer endRange = null;
        StringTokenizer st = new StringTokenizer(range,"-");  
        while(st.hasMoreTokens()) { 
            startRange = Integer.parseInt(st.nextToken()); 
            endRange= Integer.parseInt(st.nextToken()); 
        } 
        StringBuilder sb = new StringBuilder();
        // here, the "<=" was changed to "<"
        for (int i = startRange; i < endRange; i++) {
            sb.append(i).append(",");
        }
        // append last element
        sb.append(endrange)
        System.out.println(sb);

Answer 3

您在每个 i 之后附加 "," 尝试仅在未达到 endRange

时附加 ","

做：

for (int i = startRange; i <= endRange; i++) {
            sb.append(i)
            if (i != endRange)
              sb.append(",");
        }

这样","不会在最后一个号码后添加到sb。

Answer 4

Java < 8.

使用 Joiner (guava)

List<Integer> numbers = Lists.newArrayList(1, 3, 4, 5, 23);
System.out.println(Joiner.on(",").join(numbers));

输出为：

1,3,4,5,23

Answer 5

就这么简单

for (int i = startRange; i <= endRange; i++) {
   sb.append(i);
   if(i != endRange)
        sb.append(",");
}

Answer 6

如@Jan 所说，如果你有 Java8，请使用 StringJoiner。否则，您可以在新条目之前添加一个分隔符，并通过将分隔符初始化为空白来区别对待第一项。

   String separator = "";
    for (int i = startRange; i <= endRange; i++) {
        sb.append(separator).append(i);
        separator = ",";
    }

这是Java8版本

    StringJoiner sb = new StringJoiner(",");
    for (int i = startRange; i <= endRange; i++) {
        sb.add(String.valueOf(i));
    }

使用 StringBuilder 时从 last 中删除逗号

Removed comma from last while working with StringBuilder

java

stringbuilder

stringbuffer