1 语法

Collectors.joining() 会根据指定的连接符，将所有元素连接成一个字符串

//无参数--等价于 joining("");
joining()
//一个参数
joining(CharSequence delimiter)
//三个参数(前缀+后缀)
joining(CharSequence delimiter, CharSequence prefix,CharSequence suffix)

2 举个例子

/**
 * Stream流数据--多级分组操作
 * 备注：切记Stream流只能被消费一次,流就失效了
 * 如下只是示例代码
 * @author liuzebiao
 */
public class CollectDataToArray{
 
    public static void main(String[] args) {
        Stream<Student> studentStream = Stream.of(
                new Student("赵丽颖", 52, 95),
                new Student("杨颖", 56, 88),
                new Student("迪丽热巴", 56, 55),
                new Student("柳岩", 52, 33)
        );
        
        //拼接操作
        //无参:join()
        String joinStr1 = studentStream.map(s -> s.getName()).collect(Collectors.joining());
        System.out.println(joinStr1);
        //一个参数:joining(CharSequence delimiter)
        String joinStr2 = studentStream.map(s -> s.getName()).collect(Collectors.joining(","));
        System.out.println(joinStr2);
        //三个参数:joining(CharSequence delimiter, CharSequence prefix,CharSequence suffix)
        String joinStr3 = studentStream.map(s -> s.getName()).collect(Collectors.joining("—","^_^",">_<"));
        System.out.println(joinStr3);
    }
}

3 输出结果

赵丽颖杨颖迪丽热巴柳岩
赵丽颖,杨颖,迪丽热巴,柳岩
^^赵丽颖—杨颖—迪丽热巴—柳岩><