import java.util.StringJoiner;

public class Main {

    public static void main(String[] args) {

        String[] fields = { "name", "position", "salary" };

        String table = "employee";

        String select = buildSelectSql(table, fields);

        System.out.println(select);

        System.out.println("SELECT name, position, salary FROM employee".equals(select) ? "测试成功" : "测试失败");

    }

 static String buildSelectSql(String table, String[] fields) {

        String a = "SELECT ";

        var js = new StringJoiner(", ","SELECT "," FROM ");

        for(String s : fields){

            js.add(s);

}

       /***

第二种方法使用String.join（）方法。

var js = String.join(", ",fields);

        String b = " FROM ";

        return a + js + b + table;***/

        return js + table;

    }

}