Java StringJoiner Example

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Introduction

The StringJoiner class in Java is part of the java.util package and was introduced in Java 8. It constructs a sequence of characters separated by a delimiter, optionally starting with a supplied prefix and ending with a supplied suffix. This class can be particularly useful when concatenating multiple strings with a specific delimiter.

Basic Usage of StringJoiner
Using Prefix and Suffix
Merging StringJoiner Instances
Complete Example Program
Conclusion

1. Basic Usage of StringJoiner

The simplest usage of StringJoiner involves specifying a delimiter to separate the strings.

Example:

import java.util.StringJoiner;

public class StringJoinerBasicExample {
    public static void main(String[] args) {
        // Create a StringJoiner with a delimiter
        StringJoiner joiner = new StringJoiner(", ");

        // Add strings to the StringJoiner
        joiner.add("Apple");
        joiner.add("Banana");
        joiner.add("Cherry");

        // Convert the StringJoiner to a String
        String result = joiner.toString();

        System.out.println("Joined String: " + result);
    }
}

Output:

Joined String: Apple, Banana, Cherry

Explanation:

A StringJoiner is created with a comma and a space (,) as the delimiter.
Strings are added to the StringJoiner using the add() method.
The toString() method is used to convert the StringJoiner to a String.

2. Using Prefix and Suffix

You can also specify a prefix and suffix to be added to the resulting string.

Example:

import java.util.StringJoiner;

public class StringJoinerWithPrefixSuffix {
    public static void main(String[] args) {
        // Create a StringJoiner with a delimiter, prefix, and suffix
        StringJoiner joiner = new StringJoiner(", ", "[", "]");

        // Add strings to the StringJoiner
        joiner.add("Apple");
        joiner.add("Banana");
        joiner.add("Cherry");

        // Convert the StringJoiner to a String
        String result = joiner.toString();

        System.out.println("Joined String with Prefix and Suffix: " + result);
    }
}

Output:

Joined String with Prefix and Suffix: [Apple, Banana, Cherry]

Explanation:

A StringJoiner is created with a comma and a space as the delimiter, [ as the prefix, and ] as the suffix.
The resulting string includes the prefix and suffix.

3. Merging StringJoiner Instances

You can merge two StringJoiner instances using the merge() method.

Example:

import java.util.StringJoiner;

public class StringJoinerMergeExample {
    public static void main(String[] args) {
        // Create the first StringJoiner
        StringJoiner joiner1 = new StringJoiner(", ", "{", "}");
        joiner1.add("Apple");
        joiner1.add("Banana");

        // Create the second StringJoiner
        StringJoiner joiner2 = new StringJoiner(", ");
        joiner2.add("Cherry");
        joiner2.add("Date");

        // Merge the second StringJoiner into the first one
        joiner1.merge(joiner2);

        // Convert the merged StringJoiner to a String
        String result = joiner1.toString();

        System.out.println("Merged StringJoiner: " + result);
    }
}

Output:

Merged StringJoiner: {Apple, Banana, Cherry, Date}

Explanation:

Two StringJoiner instances are created and populated with strings.
The merge() method merges the second StringJoiner into the first one.
The resulting string includes all the elements from both StringJoiner instances, separated by the delimiter of the first StringJoiner.

4. Complete Example Program

Here is a complete program that demonstrates the different methods of using StringJoiner.

Example Code:

import java.util.StringJoiner;

public class StringJoinerExample {
    public static void main(String[] args) {
        // Basic Usage
        StringJoiner joinerBasic = new StringJoiner(", ");
        joinerBasic.add("Apple");
        joinerBasic.add("Banana");
        joinerBasic.add("Cherry");
        System.out.println("Basic Usage: " + joinerBasic.toString());

        // Usage with Prefix and Suffix
        StringJoiner joinerWithPrefixSuffix = new StringJoiner(", ", "[", "]");
        joinerWithPrefixSuffix.add("Apple");
        joinerWithPrefixSuffix.add("Banana");
        joinerWithPrefixSuffix.add("Cherry");
        System.out.println("With Prefix and Suffix: " + joinerWithPrefixSuffix.toString());

        // Merging StringJoiner Instances
        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("Merged StringJoiner: " + joiner1.toString());
    }
}

Output:

Basic Usage: Apple, Banana, Cherry
With Prefix and Suffix: [Apple, Banana, Cherry]
Merged StringJoiner: {Apple, Banana, Cherry, Date}

5. Conclusion

The StringJoiner class in Java provides a flexible and efficient way to concatenate multiple strings with a specified delimiter, prefix, and suffix. It is particularly useful for creating formatted output and generating CSV-like strings. By understanding and using the different methods of StringJoiner, you can simplify and streamline your string concatenation tasks.

Happy coding!

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