String join()

今天刷LeetCode的时候看题析，看到一个未曾使用过的方法String.join()

    /**
     * Creates a new String by putting each element together joined by the delimiter. If an element is null, then "null" is used as string to join.
     *
     * @param delimiter
     *          Used as joiner to put elements together
     * @param elements
     *          Elements to be joined
     * @return string of joined elements by delimiter
     * @throws NullPointerException
     *          if one of the arguments is null
     *
     */
    public static String join(CharSequence delimiter, CharSequence... elements) {
        StringJoiner stringJoiner = new StringJoiner(delimiter);

        for (CharSequence element : elements) {
            stringJoiner.add(element);
        }

        return stringJoiner.toString();
    }

注释说明这个方法是将后面的可变参数的内容通过前面的delimiter分隔符连接在一起，如果一个内容是null，那么“null”将会作为字符串放到连接中。

可以看到这里新建了一个StringJoiner对象，里面的具体实现往后再看，这里我们只需要明白这个方法是将elements中的对象通过delimiter连接起来就行，例如：

List names=new ArrayList<String>();

names.add("1");

names.add("2");

names.add("3");

System.out.println(String.join("-", names));

 

String[] arrStr=new String[]{"a","b","c"};

System.out.println(String.join("-", arrStr));


输出：
1-2-3
a-b-c