str1.concat(str2);

或者

"str1" + "str2";

// Scala program to illustrate how to 
// concatenate strings
object GFG
{
       
    // str1 and str2 are two strings
    var str1 = "Welcome! GeeksforGeeks "
    var str2 = " to Portal"
       
    // Main function
    def main(args: Array[String])
    {
           
        // concatenate str1 and str2 strings
        // using concat() function
        var Newstr = str1.concat(str2);
           
        // Display strings 
        println("String 1:" +str1);
        println("String 2:" +str2);
        println("New String :" +Newstr);
           
        // Concatenate strings using '+' operator
        println("This is the tutorial" + 
                    " of Scala language" + 
                    " on GFG portal");
    }
}

String 1:Welcome! GeeksforGeeks 
String 2: to Portal
New String :Welcome! GeeksforGeeks  to Portal
This is the tutorial of Scala language on GFG portal

// Scala program to illustrate how to
// concatenate strings
 
// Creating object
object GFG
{
    // Main method
   def main(args: Array[String])
   {
        var str1 = "Welcome to ";
        var str2 =  "GeeksforGeeks";
       
        // Concatenating two string
        println("After concatenate two string: " + str1 + str2);
   }
}

After concatenate two string: Welcome toGeeksforGeeks