Java StringJoiner

Java added a new final class StringJoiner in java.util package. It is used to construct a sequence of characters separated by a delimiter. Now, you can create string by passing delimiters like comma(,), hyphen(-) etc. You can also pass prefix and suffix to the char sequence.

StringJoiner Constructors

Constructor	Description
Public StringJoiner(CharSequence delimiter)	It constructs a StringJoiner with no characters in it, with no prefix or suffix, and a copy of the supplied delimiter. It throws NullPointerException if delimiter is null.
Public StringJoiner(CharSequence delimiter,CharSequence prefix,CharSequence suffix)	It constructs a StringJoiner with no characters in it using copies of the supplied prefix, delimiter and suffix. It throws NullPointerException if prefix, delimiter, or suffix is null.

StringJoiner Methods

Method	Description
Public StringJoiner add(CharSequence newElement)	It adds a copy of the given CharSequence value as the next element of the StringJoiner value. If newElement is null,"null" is added.
Public StringJoiner merge(StringJoiner other)	It 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.
Public int length()	It returns the length of the String representation of this StringJoiner.
Public StringJoiner setEmptyValue(CharSequence emptyValue)	It 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.

Java StringJoiner Example

// importing StringJoiner class
import java.util.StringJoiner;
public class StringJoinerExample {
	public static void main(String[] args) {
		StringJoiner joinNames = new StringJoiner(",");	// passing comma(,) as delimiter 
		
		// Adding values to StringJoiner
		joinNames.add("Rahul");
		joinNames.add("Raju");
		joinNames.add("Peter");
		joinNames.add("Raheem");
				
		System.out.println(joinNames);
	}
}

Output:

Rahul,Raju,Peter,Raheem

Java StringJoiner Example: adding prefix and suffix

// importing StringJoiner class
import java.util.StringJoiner;
public class StringJoinerExample {
	public static void main(String[] args) {
		StringJoiner joinNames = new StringJoiner(",", "[", "]");	// passing comma(,) and square-brackets as delimiter 
		
		// Adding values to StringJoiner
		joinNames.add("Rahul");
		joinNames.add("Raju");
		joinNames.add("Peter");
		joinNames.add("Raheem");
				
		System.out.println(joinNames);
	}
}

Output:

[Rahul,Raju,Peter,Raheem]

StringJoiner Example: Merge Two StringJoiner

The merge() method merges two StringJoiner objects excluding of prefix and suffix of second StringJoiner object.

// importing StringJoiner class
import java.util.StringJoiner;
public class StringJoinerExample {
	public static void main(String[] args) {

		StringJoiner joinNames = new StringJoiner(",", "[", "]");	// passing comma(,) and square-brackets as delimiter 
		
		// Adding values to StringJoiner
		joinNames.add("Rahul");
		joinNames.add("Raju");

		// Creating StringJoiner with :(colon) delimiter
		StringJoiner joinNames2 = new StringJoiner(":", "[", "]");	// passing colon(:) and square-brackets as delimiter 
		
		// Adding values to StringJoiner
		joinNames2.add("Peter");
		joinNames2.add("Raheem");

		// Merging two StringJoiner
		StringJoiner merge = joinNames.merge(joinNames2); 
		System.out.println(merge);
	}
}

Output:

[Rahul,Raju,Peter:Raheem]

StringJoiner Example: StringJoiner Methods

// importing StringJoiner class
import java.util.StringJoiner;
public class StringJoinerExample {
	public static void main(String[] args) {
		StringJoiner joinNames = new StringJoiner(",");	// passing comma(,) as delimiter 
		
		// Prints nothing because it is empty
		System.out.println(joinNames);
		
		// We can set default empty value.
		joinNames.setEmptyValue("It is empty");
		System.out.println(joinNames);
		
		
		// Adding values to StringJoiner
		joinNames.add("Rahul");
		joinNames.add("Raju");
		System.out.println(joinNames);
		
		// Returns length of StringJoiner
		int length = joinNames.length();
		System.out.println("Length: "+length);
		
		// Returns StringJoiner as String type 
		String str = joinNames.toString();
		System.out.println(str);
		
		// Now, we can apply String methods on it
		char ch = str.charAt(3);
		System.out.println("Character at index 3: "+ch);
		
		// Adding one more element 
		joinNames.add("Sorabh");
		System.out.println(joinNames);
		
		// Returns length
		int newLength = joinNames.length();
		System.out.println("New Length: "+newLength);
	}
}

Output:

It is empty
Rahul,Raju
Length: 10
Rahul,Raju
Character at index 3: u
Rahul,Raju,Sorabh
New Length: 17

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