Java ArrayList StringBuilder追加

Question

I have one problem when appending List values as String. I will be getting 1 or more than 1 value into the list. Then I need to append these string as one string and use a separator , for each string. But at the end also the comma is getting added. How Can I remove this at the end of the string dynamically. Here is my code:

cntList = parseXml(metadata.xml);
if (cntList.size() != 0) {
    // entryCountryMap.put(id, country);
    System.out.println("Size is  ---->" + cntList.size());
    StringBuilder sb = new StringBuilder();
    if (cntList.size() >= 2) {
        for (String s : cntList) {
            sb.append(s);
            sb.append(",");
        }
    }
    System.out.println("StringBuilder ----->" + sb.toString());
}

And my output is like this:

StringBuilder ----->All Countries,US - United States,

Please help me resolving this. Thanks - Raji

Answer 1

With java 8 it's a one liner

String.join(",", cntList);

If you need to filter the elements of the list and/or mutate the strings before joining to a single string, you can still do it in a very concise manner without loops.

cntList.stream().filter(...).map(...).collect(Collectors.joining(","));

(the ... need to be replaced by your filtering predicate and your mapper)

Answer 2

I would use normal for loop. The last one append outside the for loop without comma

if (cntList.size() >= 2) {
    for (int i=0;i<cntList.size()-1;i++) {
        sb.append(cntList.get(i));
        sb.append(",");
    }
    sb.append(cntList.get(cntList.size()-1));
}

Answer 3

Simply delete the last character:

StringBuilder sb = new StringBuilder("foo,");
System.out.println(sb.deleteCharAt(sb.length() - 1)); 

Output

foo

More dynamically, you can find the last comma by index and delete that plus anything that comes after:

sb.delete(sb.lastIndexOf(","), sb.length());

As Pshemo points out:

sb.setLength(sb.length() - 1); will actually perform better than sb.deleteCharAt(sb.length() - 1) .