Unlike Java, Kotlin supports string interpolation where an actual variable, an expression value, can be used to substitute placeholders ($ sign followed by the variable name or $ sign followed by curly braces) inside string objects. This eliminates the need for memory-expensive string concatenation using the + operator in Java. This is explained using the following code:

var sum: Double = calculator.add(1.0, 2.0);
println("Double Sum of 1.0 + 2.0 = $sum");

...
println("No of times methods invoked in StringFormatter = ${stringFormatter.noOfTimesMethodsInvoked}");

In the preceding code snippet println, which is passed with string objects containing the placeholders $sum and ${stringFormatter.noOfTimesMethodsInvoked} respectively. Kotlin will replace the actual values with the placeholders before they're sent to be printed on the console.