How do I append a newline character for all lines except the last one?

Question

I'm iterating through a HashMap (see my earlier question for more detail) and building a string consisting of the data contained in the Map. For each item, I will have a new line, but for the very last item, I don't want the new line. How can I achieve this? I was thinking I could so some kind of check to see if the entry is the last one or not, but I'm not sure how to actually do that.

Thanks!

Answer 1

Change your thought process from "append a line break all but the last time" to "prepend a line break all but the first time":

boolean first = true;
StringBuilder builder = new StringBuilder();

for (Map.Entry<MyClass.Key,String> entry : data.entrySet()) {
    if (first) {
        first = false;
    } else {
        builder.append("\n"); // Or whatever break you want
    }
    builder.append(entry.key())
           .append(": ")
           .append(entry.value());
}

Answer 2

Assuming your foreach loop goes through the file in order just add a new line to every string and remove the last new line when your loop exits.

Answer 3

Not sure if this is the best, but it´s the easier way to do:

loop through all the values and append the \n normally in the stringbuffer. Then, do something like this

sb.setLength(sb.length()-1);

Answer 4

one method (with apologies to Jon Skeet for borrowing part of his Java code):

StringBuilder result = new StringBuilder();

string newline = "";  
for (Map.Entry<MyClass.Key,String> entry : data.entrySet())
{
    result.append(newline)
       .append(entry.key())
       .append(": ")
       .append(entry.value());

    newline = "\n";
}

Answer 5

Ususally for these kind of things I use apache-commons-lang StringUtils#join. While it's not really hard to write all these kinds of utility functionality, it's always better to reuse existing proven libraries. Apache-commons is full of useful stuff like that!

Answer 6

If you use iterator instead of for...each your code could look like this:

StringBuilder builder = new StringBuilder();

Iterator<Map.Entry<MyClass.Key, String>> it = data.entrySet().iterator();

while (it.hasNext()) {
    Map.Entry<MyClass.Key, String> entry = it.next();

    builder.append(entry.key())
    .append(": ")
    .append(entry.value());

    if (it.hasNext()) {
        builder.append("\n");
    }
}

Answer 7

Here's my succinct version, which uses the StringBuilder's length property instead of an extra variable:

StringBuilder builder = new StringBuilder();

for (Map.Entry<MyClass.Key,String> entry : data.entrySet())
{
    builder.append(builder.length() > 0 ? "\n" : "")
           .append(entry.key())
           .append(": ")
           .append(entry.value());
}

(Apologies and thanks to both Jon and Joel for "borrowing" from their examples.)

Answer 8

What about this?

StringBuilder result = new StringBuilder();

for(Map.Entry<MyClass.Key,String> entry : data.entrySet())
{
    builder.append(entry.key())
       .append(": ")
       .append(entry.value())
       .append("\n");
}

return builder.substring(0, builder.length()-1);

Obligatory apologies and thanks to both Jon and Joel for "borrowing" from their examples.

Answer 9

This is where a join method, to complement split, would come in handy, because then you could just join all the elements using a new line as the separator, and of course it doesn't append a new line to the end of the result; that's how I do it in various scripting languages (Javascript, PHP, etc.).

Answer 10

If you use Class Separator, you can do

StringBuilder buf = new StringBuilder();
Separator separator = new Separator("\n");
for (Map.Entry<MyClass.Key,String> entry: data.entrySet()) {
    builder.append(separator)
       .append(entry.key())
       .append(": ")
       .append(entry.value());
}

The separator prints in empty string upon its first use, and the separator upon all subsequent uses.