Adding parentheses to each item in HashSet

Question

Dear All,
Having almost completed my first java tool which queries a database to allow user-defined filtering, I'm running into a last 'small' problem:
I won't bore you guys with the whole thing, but instead will just focus on the part where i'm stuck, in the hope that somebody can give me a useful tip as to how to solve this! Thanks very much in advance for any input!
Basically, what it comes down to is that I query the database twice, resulting in two lists of data stored as HashSets in Java, to then work out the intersect of them both with the listI.retainAll(listII) function. Finally, I want to use the merged list to query the database again, using the variables listed in the final set. In order to use the list in the query, I first convert the HashSet to a string as follows:
String convList = listI.toString();As this results in a string with square brackets [] and mySQL needs regular brackets, I convert them like this:
convList = convList.replace('[', '(');
convList = convList.replace(']', ')');This will result in something along the lines as (result1, result2, result3, result4, etc.). The problem is though, that I would need it to be like
("result1", "result2", "result3", "result4") in order for mySQL to accept it using the IN clause.
I tried to add the parentheses using:
convList = convList.replaceAll(',', '",');
        convList = convList.replaceAll(' ', ' "');but the Java compiler complains of an error with "unclosed character literal", so I was hoping somebody could maybe give me a hint as to how I can add parentheses for each member in the list? Thanks alot in advance

Answer 1

les_paulde wrote:
wow, thanks for your swift reply! This definitely solved my problem and I can now run the query. The code turned out as follows:
String convList = listI.toString();
convList = convList.replace("[", "(\"");
convList = convList.replace("]", "\")");
convList = convList.replaceAll(",", "\",");
convList = convList.replaceAll(" ", " \"");
And what happens if the String representation of the object in your list contains one of the characters you're replacing? It will go awfully wrong!
This is safer:
public static String asString(List<?> list) {
    StringBuilder b = new StringBuilder();
    b.append('(');
    for(int i = 0; i < list.size(); i++) {
        b.append('"').append(list.get(i)).append('"');
        if(i < list.size()-1) b.append(", ");
    return b.append(')').toString();
System.out.println(asString(listI));