Java中的StringJoiner类使用示例深入详解

package java.util;
public final class StringJoiner {
    private final String prefix;
    private final String delimiter;
    private final String suffix;
    private StringBuilder value;
    private String emptyValue;
    public StringJoiner(CharSequence delimiter) {
        this(delimiter, "", "");
    }
    public StringJoiner(CharSequence delimiter,
                        CharSequence prefix,
                        CharSequence suffix) {
        Objects.requireNonNull(prefix, "The prefix must not be null");
        Objects.requireNonNull(delimiter, "The delimiter must not be null");
        Objects.requireNonNull(suffix, "The suffix must not be null");
        // make defensive copies of arguments
        this.prefix = prefix.toString();
        this.delimiter = delimiter.toString();
        this.suffix = suffix.toString();
        this.emptyValue = this.prefix + this.suffix;
    }
}

public StringJoiner add(CharSequence newElement) {
    prepareBuilder().append(newElement);
    return this;
}
private StringBuilder prepareBuilder() {
    if (value != null) {
        value.append(delimiter);
    } else {
        value = new StringBuilder().append(prefix);
    }
    return value;
}

public static void main(String[] args) {
    StringJoiner stringJoiner = new StringJoiner(",","[","]");
    stringJoiner.add("x") .add("j");
    StringJoiner stringJoiner1 = new StringJoiner(",","(",")");
    stringJoiner1.add("x1").add("j1");
    System.out.println(stringJoiner.toString());
    System.out.println(stringJoiner1.toString());
    System.out.println(stringJoiner1.merge(stringJoiner).toString());
    System.out.println(stringJoiner1.toString());
    System.out.println(stringJoiner.merge(stringJoiner1).toString());
}

list.stream().collect(Collectors.joining(","));

public static Collector<CharSequence, ?, String> joining(CharSequence delimiter) {
  return joining(delimiter, "", "");
}
public static Collector<CharSequence, ?, String> joining(CharSequence delimiter,
                                                         CharSequence prefix,
                                                         CharSequence suffix) {
    return new CollectorImpl<>(
            () -> new StringJoiner(delimiter, prefix, suffix),
            StringJoiner::add, StringJoiner::merge,
            StringJoiner::toString, CH_NOID);
}