Detailed code explanation of Java8 StringJoiner

Finally, Java 8 released the StringJoiner class under the java.util package. I don't think this is a radically different implementation than our old-school approach of using StringBuffer/StringBuilder to concatenate strings. Let's take a look at the usage of StringJoiner and its internal implementation. For example, I have two strings called "Smart" and "Techie", and I want to concatenate these strings into [Smart, Techie]. In this case, my prefix is ​​"[", suffix is ​​"]", and delimiter is ",". StringJoiner has the following two

.

StringJoiner(CharSequence delimiter)

StringJoiner(CharSequence delimiter, CharSequence prefix, CharSequence suffix)

StringJoiner sjr = new StringJoiner(",", "[", "]");
sjr.add("Smart").add("Techie");
System.out.println("The final Joined string is " + sjr);

If we don’t want to have prefix and suffix, then just:

sjr1.add("Smart").add("Techie");
System.out.println("The final Joined string is " + sjr1);

Now, we will see the implementation of add and toString() methods.

public StringJoiner add(CharSequence newElement) {
   prepareBuilder().append(newElement);
   return this;
}

prepareBuilder() is implemented as follows.

private StringBuilder prepareBuilder() {
    if (value != null) {
       value.append(delimiter);
    } else {
       value = new StringBuilder().append(prefix);
    }
    return value;
}

From the above implementation, it is obvious that StringJoiner follows the old-fashioned approach.

toString() is implemented as follows.

public String toString() {
    if (value == null) {
      return emptyValue;
    } else {
    if (suffix.equals("")) {
      return value.toString();
    } else {
    int initialLength = value.length();
    String result = value.append(suffix).toString();
    // reset value to pre-append initialLength
    value.setLength(initialLength);
    return result;
    }
}

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