What's the best way to build a string of delimited items in Java?

java

string-join

string-builder

performance-optimization

byAlex Kataev·Mar 12, 2025

Join strings seamlessly with StringJoiner in Java 8:

StringJoiner stringJoiner = new StringJoiner(", "); // Hanging out with commas...
stringJoiner.add("Apple").add("Banana").add("Cherry");
String result = stringJoiner.toString();
// "I've got: Apple, Banana, Cherry"

Outside the realm of Java 8, StringBuilder is your reliable workhorse:

StringBuilder builder = new StringBuilder();
// Let's do some fruit shopping!
for (String fruit : Arrays.asList("Apple", "Banana", "Cherry")) {
    if (builder.length() > 0) builder.append(", ");
    builder.append(fruit);
}
String result = builder.toString();
// "I've got: Apple, Banana, Cherry"

Simpler join with `String.join` and `TextUtils.join`

When using collections, Java 8 pulled a rabbit out of its hat with String.join:

// Going to the fruit market!
List<String> fruits = Arrays.asList("Apple", "Banana", "Cherry");
String result = String.join(", ", fruits); // "Apple, Banana, Cherry"

For the Android aficionados, Android's TextUtils.join has got you covered:

String result = TextUtils.join(", ", new String[]{"Apple", "Banana", "Cherry"});
// And Look, I did the groceries in Android!

Looking beyond Java? The handy StringUtils.join function from Apache Commons Lang library has your back:

String result = StringUtils.join(fruits, ", "); // "Apple, Banana, Cherry"

Nulls and empty lists: Uninvited guests, anyone?

Check uninvited guests while building strings - handle potential empty lists or null elements:

StringJoiner joiner = new StringJoiner(", ");
fruits.stream()
    .filter(Objects::nonNull) // No null party crashers allowed!
    .forEach(joiner::add);
String result = joiner.toString();

Performance matters: Optimizing StringBuilder

Adding StringBuilder capacity upfront is worth considering when dealing with larger datasets:

int approximateSize = fruits.size() * estimatedItemSize;
StringBuilder builder = new StringBuilder(approximateSize);
// Give me some space... I've got heavy lifting to do!

Guava's Joiner: The alternative approch

Need a tool with some extra muscle? Try Guava's Joiner:

String result = Joiner.on(", ").skipNulls().join(fruits); 
// Heard about the skipping nulls party trick?

Handle delimiter: It's not just about commas!

In handmade string builds, don't get tripped over by improper delimiter management:

// Look I've got an extra tail! 🐒
String result = builder.toString(); // "Apple, Banana, Cherry,"

Say Hi to i18n: Going global friendly

Remember to account for i18n when creating globally-conscious applications:

// Single string, many languages
Locale locale = ...;
String delimiter = ResourceBundle.getBundle("delimiters", locale).getString("list_delimiter");
StringJoiner joiner = new StringJoiner(delimiter);
// ... Add elements