---

id: 115

slug: "string-join"

title: "String.join() for delimiters"

category: "strings"

difficulty: "beginner"

jdkVersion: "8"

oldLabel: "Manual loop"

modernLabel: "Java 8+"

oldApproach: "StringBuilder delimiter logic"

modernApproach: "String.join()"

oldCode: |-

StringBuilder csv = new StringBuilder();

for (String name : names) {

if (csv.length() > 0) {

csv.append(", ");

}

csv.append(name);

}

String result = csv.toString();

modernCode: |-

String result = String.join(", ", names);

summary: "Replace manual delimiter bookkeeping with String.join() for readable joined strings."

explanation: "Building a delimited string by hand usually means tracking whether you are on the first element, appending separators conditionally, and finally converting the builder to a string. String.join() expresses the intent directly: join these values with this delimiter. It is ideal for labels, CSV-like output, logs, and small display strings."

whyModernWins:

- icon: "✂️"

title: "Less code"

desc: "No first-element flag, conditional comma, or manual builder lifecycle."

- icon: "👁"

title: "Intent first"

desc: "The delimiter and values are visible in a single expression."

- icon: "🧩"

title: "Works with iterables"

desc: "Use it with arrays, lists, sets, or any Iterable of CharSequence values."

support:

state: "available"

description: "Available since JDK 8 (March 2014)"

prev: "collections/comparator-null-handling"

next: "streams/collectors-filtering"

related:

- "strings/string-formatted"

- "strings/multiline-json-sql"

- "streams/stream-tolist"

docs:

- title: "String.join() Javadoc"

href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/String.html#join(java.lang.CharSequence,java.lang.Iterable)"