Java StringJoiner Class

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Introduction

The StringJoiner class in Java, part of the java.util package, 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. 

It was introduced in Java 8 as a utility to make it easier to create delimited strings, particularly useful in scenarios where you need to join strings with a specific delimiter.

Table of Contents

1. What is the StringJoiner Class?
2. Common Methods
3. Examples of Using the StringJoiner Class
4. Conclusion

1. What is the StringJoiner Class?

The StringJoiner class is designed to concatenate strings with a specified delimiter and optional prefix and suffix. This class provides a convenient way to build a single string from multiple parts with consistent formatting.

2. Common Methods

• add(CharSequence newElement): Adds a copy of the given CharSequence value as the next element of the StringJoiner value.
• toString(): Returns the string representation of the StringJoiner instance, including the prefix, the delimiter, and the suffix.
• setEmptyValue(CharSequence emptyValue): Sets the sequence of characters to be used when the StringJoiner is empty.
• length(): Returns the length of the string (in characters) constructed so far.

3. Examples of Using the StringJoiner Class

Example 1: Basic Usage of StringJoiner

This example demonstrates basic usage of the StringJoiner to join strings with a delimiter.

import java.util.StringJoiner;

public class BasicStringJoinerExample {
    public static void main(String[] args) {
        StringJoiner joiner = new StringJoiner(", ");

        joiner.add("Apple");
        joiner.add("Banana");
        joiner.add("Cherry");

        System.out.println(joiner.toString());
    }
}

Output:

Apple, Banana, Cherry

Example 2: Using Prefix and Suffix

This example shows how to use StringJoiner with a prefix and suffix.

import java.util.StringJoiner;

public class PrefixSuffixExample {
    public static void main(String[] args) {
        StringJoiner joiner = new StringJoiner(", ", "[", "]");

        joiner.add("Apple");
        joiner.add("Banana");
        joiner.add("Cherry");

        System.out.println(joiner.toString());
    }
}

Output:

[Apple, Banana, Cherry]

Example 3: Using setEmptyValue

This example demonstrates how to set a default value for an empty StringJoiner.

import java.util.StringJoiner;

public class SetEmptyValueExample {
    public static void main(String[] args) {
        StringJoiner joiner = new StringJoiner(", ");
        joiner.setEmptyValue("No fruits");

        System.out.println(joiner.toString()); // Prints "No fruits"

        joiner.add("Apple");
        joiner.add("Banana");

        System.out.println(joiner.toString()); // Prints "Apple, Banana"
    }
}

Output:

No fruits
Apple, Banana

Example 4: Merging Two StringJoiner Instances

This example demonstrates how to merge two StringJoiner instances.

import java.util.StringJoiner;

public class MergeStringJoinerExample {
    public static void main(String[] args) {
        StringJoiner joiner1 = new StringJoiner(", ");
        joiner1.add("Apple");
        joiner1.add("Banana");

        StringJoiner joiner2 = new StringJoiner("; ");
        joiner2.add("Cherry");
        joiner2.add("Date");

        joiner1.merge(joiner2);

        System.out.println(joiner1.toString());
    }
}

Output:

Apple, Banana, Cherry; Date

Example 5: Getting the Length of the Joined String

This example demonstrates how to get the length of the string constructed by StringJoiner.

import java.util.StringJoiner;

public class StringJoinerLengthExample {
    public static void main(String[] args) {
        StringJoiner joiner = new StringJoiner(", ");
        joiner.add("Apple");
        joiner.add("Banana");
        joiner.add("Cherry");

        System.out.println("Joined String: " + joiner.toString());
        System.out.println("Length: " + joiner.length());
    }
}

Output:

Joined String: Apple, Banana, Cherry
Length: 21

4. Conclusion

The StringJoiner class in Java provides a convenient way to construct delimited strings with optional prefix and suffix. It simplifies the process of joining multiple strings into a single formatted string. The examples provided demonstrate common usage patterns and highlight the capabilities of the StringJoiner class, making it used for string manipulation tasks in Java.