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Java Dictionary

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String.split() / String.join()

String.split() / String.join()

Methods for splitting a string into an array using a delimiter, and for joining an array or multiple strings with a delimiter. Widely used for parsing CSV data and generating formatted output.

Syntax

// Splits a string using a regular expression and returns a String array.
str.split(String regex);
str.split(String regex, int limit);

// Joins multiple strings with a delimiter (Java 8 and later).
String.join(CharSequence delimiter, CharSequence... elements);
String.join(CharSequence delimiter, Iterable<? extends CharSequence> elements);

// Formats a string using a format specifier.
String.format(String format, Object... args);

Method List

Method	Description
split(String regex)	Splits the string at positions matching the regular expression and returns a `String[]`. Trailing empty strings are removed.
split(String regex, int limit)	Specifies the maximum number of substrings to return. A negative value preserves trailing empty strings.
String.join(delimiter, elements)	Returns a new string by joining multiple strings with the specified delimiter.
String.format(format, args)	Returns a string with arguments inserted according to the format specifier. Supports `printf`-style formatting.

Sample Code

// Split a comma-separated string with split().
String csv = "apple,banana,cherry";
String[] fruits = csv.split(",");
for (String fruit : fruits) {
    System.out.println(fruit); // Prints "apple", "banana", and "cherry" in order.
}

// Limit the number of resulting substrings.
String data = "a:b:c:d";
String[] parts = data.split(":", 2); // Split into at most 2 parts.
System.out.println(parts[0]); // Prints "a".
System.out.println(parts[1]); // Prints "b:c:d".

// Join an array with String.join().
String joined = String.join(", ", "Java", "Python", "Swift");
System.out.println(joined); // Prints "Java, Python, Swift".

// Join a List.
java.util.List<String> list = java.util.Arrays.asList("赤", "青", "緑");
System.out.println(String.join(" / ", list)); // Prints "赤 / 青 / 緑".

// Build a formatted string with String.format().
String msg = String.format("Name: %s, Age: %d", "Taro Yamada", 30);
System.out.println(msg); // Prints "Name: Taro Yamada, Age: 30".

// Display a decimal value with two decimal places.
double price = 1234.5;
System.out.println(String.format("Price: %.2f", price)); // Prints "Price: 1234.50".

Notes

split() treats its argument as a regular expression. If you use characters with special meaning in regex — such as a period (.) or pipe (|) — as delimiters, you must escape them: \\. or \\|.

String.join() is a static method added in Java 8 that makes it easy to join arrays and lists. For more complex string manipulation, using StringBuilder's append() is more efficient.

To replace parts of a string, use replace() / replaceAll(). To convert between a string and a character array, use toCharArray().

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