Java中的 String.join() 将列表以某个字符串分隔组装为一个字符串 （之前我都不知道，自己写方法）

       之前用Python，有个很方便的 list.join 方法，将列表中的字符串以 特殊字符分隔 组装为一个字符串，后来换了Java，也会习惯的认为 Java的 List也会有类似的操作，但是 点不出来吖。

       所以 要用到类似的操作时都是自己 写个循环方法。

       但是，今天看同学写代码，刚好有类似的操作，然后使用了 String.join(), 当时就是一句 卧槽，原来有啊，当时就觉得这肯定得写个Blog记录下。

       介绍下这个API：注意下 @since 1.8

/**
* Returns a new String composed of copies of the
* {@code CharSequence elements} joined together with a copy of
* the specified {@code delimiter}.
*
* <blockquote>For example,
* <pre>{@code
*     String message = String.join("-", "Java", "is", "cool");
*     // message returned is: "Java-is-cool"
* }</pre></blockquote>
*
* Note that if an element is null, then {@code "null"} is added.
*
* @param  delimiter the delimiter that separates each element
* @param  elements the elements to join together.
*
* @return a new {@code String} that is composed of the {@code elements}
*         separated by the {@code delimiter}
*
* @throws NullPointerException If {@code delimiter} or {@code elements}
*         is {@code null}
*
* @see java.util.StringJoiner
* @since 1.8
*/
public static String join(CharSequence delimiter, CharSequence... elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
// Number of elements not likely worth Arrays.stream overhead.
StringJoiner joiner = new StringJoiner(delimiter);
for (CharSequence cs: elements) {
joiner.add(cs);
        }
return joiner.toString();
    }

/**
* Returns a new {@code String} composed of copies of the
* {@code CharSequence elements} joined together with a copy of the
* specified {@code delimiter}.
*
* <blockquote>For example,
* <pre>{@code
*     List<String> strings = new LinkedList<>();
*     strings.add("Java");strings.add("is");
*     strings.add("cool");
*     String message = String.join(" ", strings);
*     //message returned is: "Java is cool"
*
*     Set<String> strings = new LinkedHashSet<>();
*     strings.add("Java"); strings.add("is");
*     strings.add("very"); strings.add("cool");
*     String message = String.join("-", strings);
*     //message returned is: "Java-is-very-cool"
* }</pre></blockquote>
*
* Note that if an individual element is {@code null}, then {@code "null"} is added.
*
* @param  delimiter a sequence of characters that is used to separate each
*         of the {@code elements} in the resulting {@code String}
* @param  elements an {@code Iterable} that will have its {@code elements}
*         joined together.
*
* @return a new {@code String} that is composed from the {@code elements}
*         argument
*
* @throws NullPointerException If {@code delimiter} or {@code elements}
*         is {@code null}
*
* @see    #join(CharSequence,CharSequence...)
* @see    java.util.StringJoiner
* @since 1.8
*/
public static String join(CharSequence delimiter,
Iterable<? extends CharSequence> elements) {
Objects.requireNonNull(delimiter);
Objects.requireNonNull(elements);
StringJoiner joiner = new StringJoiner(delimiter);
for (CharSequence cs: elements) {
joiner.add(cs);
        }
return joiner.toString();
    }