StringJoiner

AI-generated Key Takeaways

• StringJoiner helps build strings with a delimiter, optional prefix, and suffix.

• It's useful for creating comma-separated values or other delimited strings.

• setEmptyValue allows specifying the output for empty StringJoiner instances.

• add appends elements, while merge combines with another StringJoiner.

• toString generates the final string representation.

public final class StringJoiner extends Object

StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.

Prior to adding something to the StringJoiner, its sj.toString() method will, by default, return prefix + suffix. However, if the setEmptyValue method is called, the emptyValue supplied will be returned instead. This can be used, for example, when creating a string using set notation to indicate an empty set, i.e. "{}", where the prefix is "{", the suffix is "}" and nothing has been added to the StringJoiner.

See Also

• Collectors.joining(CharSequence)
• Collectors.joining(CharSequence, CharSequence, CharSequence)

Public Constructor Summary

	StringJoiner(CharSequence delimiter) Constructs a StringJoiner with no characters in it, with no prefix or suffix, and a copy of the supplied delimiter.
	StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix) Constructs a StringJoiner with no characters in it using copies of the supplied prefix, delimiter and suffix.

Public Method Summary

StringJoiner	add(CharSequence newElement) Adds a copy of the given CharSequence value as the next element of the StringJoiner value.
int	length() Returns the length of the String representation of this StringJoiner.
StringJoiner	merge(StringJoiner other) Adds the contents of the given StringJoiner without prefix and suffix as the next element if it is non-empty.
StringJoiner	setEmptyValue(CharSequence emptyValue) Sets the sequence of characters to be used when determining the string representation of this StringJoiner and no elements have been added yet, that is, when it is empty.
String	toString() Returns the current value, consisting of the prefix, the values added so far separated by the delimiter, and the suffix, unless no elements have been added in which case, the prefix + suffix or the emptyValue characters are returned

Inherited Method Summary

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public StringJoiner (CharSequence delimiter)

Constructs a StringJoiner with no characters in it, with no prefix or suffix, and a copy of the supplied delimiter. If no characters are added to the StringJoiner and methods accessing the value of it are invoked, it will not return a prefix or suffix (or properties thereof) in the result, unless setEmptyValue has first been called.

Parameters

delimiter	the sequence of characters to be used between each element added to the StringJoiner value

Throws

NullPointerException	if delimiter is null

public StringJoiner (CharSequence delimiter, CharSequence prefix, CharSequence suffix)

Constructs a StringJoiner with no characters in it using copies of the supplied prefix, delimiter and suffix. If no characters are added to the StringJoiner and methods accessing the string value of it are invoked, it will return the prefix + suffix (or properties thereof) in the result, unless setEmptyValue has first been called.

Parameters

delimiter	the sequence of characters to be used between each element added to the StringJoiner
prefix	the sequence of characters to be used at the beginning
suffix	the sequence of characters to be used at the end

Throws

NullPointerException	if prefix, delimiter, or suffix is null

Public Methods

public StringJoiner add (CharSequence newElement)

Adds a copy of the given CharSequence value as the next element of the StringJoiner value. If newElement is null, then "null" is added.

Parameters

newElement	The element to add

Returns

• a reference to this StringJoiner

public int length ()

Returns the length of the String representation of this StringJoiner. Note that if no add methods have been called, then the length of the String representation (either prefix + suffix or emptyValue) will be returned. The value should be equivalent to toString().length().

Returns

• the length of the current value of StringJoiner

public StringJoiner merge (StringJoiner other)

Adds the contents of the given StringJoiner without prefix and suffix as the next element if it is non-empty. If the given StringJoiner is empty, the call has no effect.

A StringJoiner is empty if add() has never been called, and if merge() has never been called with a non-empty StringJoiner argument.

If the other StringJoiner is using a different delimiter, then elements from the other StringJoiner are concatenated with that delimiter and the result is appended to this StringJoiner as a single element.

Parameters

other	The StringJoiner whose contents should be merged into this one

Returns

• This StringJoiner

Throws

NullPointerException	if the other StringJoiner is null

public StringJoiner setEmptyValue (CharSequence emptyValue)

Sets the sequence of characters to be used when determining the string representation of this StringJoiner and no elements have been added yet, that is, when it is empty. A copy of the emptyValue parameter is made for this purpose. Note that once an add method has been called, the StringJoiner is no longer considered empty, even if the element(s) added correspond to the empty String.

Parameters

emptyValue	the characters to return as the value of an empty StringJoiner

Returns

• this StringJoiner itself so the calls may be chained

Throws

NullPointerException	when the emptyValue parameter is null

public String toString ()

Returns the current value, consisting of the prefix, the values added so far separated by the delimiter, and the suffix, unless no elements have been added in which case, the prefix + suffix or the emptyValue characters are returned

Returns

• the string representation of this StringJoiner