Java StringJoiner

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.

import java.util.StringJoiner;

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

        // passing comma(,) and square-brackets as delimiter
        StringJoiner joinNames2 = new StringJoiner(",", "[", "]");
        // Adding values to StringJoiner
        joinNames2.add("Rahul");
        joinNames2.add("Raju");
        joinNames2.add("Peter");
        joinNames2.add("Raheem");
        System.out.println(joinNames2);

        StringJoiner joinNames3 = new StringJoiner(",", "[", "]");
        joinNames3.add("Rahul");
        joinNames3.add("Raju");

        StringJoiner joinNames4 = new StringJoiner(":", "[", "]");
        joinNames4.add("Peter");
        joinNames4.add("Raheem");

        // Merging two StringJoiner
        StringJoiner merge = joinNames3.merge(joinNames4);
        System.out.println(merge);
    }
}

点击查看结果

```
Rahul,Raju,Peter,Raheem
[Rahul,Raju,Peter,Raheem]
[Rahul,Raju,Peter:Raheem]
```

import java.util.StringJoiner;

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

        // 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);
    }
}

点击查看结果

```

It is empty

Rahul,Raju

Length: 10

Rahul,Raju

Character at index 3: u

Rahul,Raju,Sorabh

New Length: 17

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**参考资料**
* [https://www.javatpoint.com/java-stringjoiner](https://www.javatpoint.com/java-stringjoiner)