Understanding Loops and Control Structures in Scala

Sometimes we need to execute the same block of code multiple times. Normally statements run sequentially: the first statement in a function executes first, then the second, and so on.

Programming languages provide various control structures for more complex execution paths.

Loop statements allow us to execute a statement or a group of statements repeatedly; below is a flowchart of loop statements used in most programming languages.

Loop Types

Scala provides several loop types. Click the links for details on each type.

Loop Type

Description

while loop

Executes a series of statements repeatedly while the condition is true, stopping when it becomes false.

do...while loop

Similar to while, but the condition is checked after the loop body, guaranteeing at least one execution.

for loop

Repeats a series of statements until a specific condition is met, typically by incrementing a counter after each iteration.

Loop Control Statements

Loop control statements alter the execution order of your code, enabling jumps. Scala offers several such statements.

Scala does not support break or continue statements, but since version 2.8 it provides a way to interrupt loops; see the linked details.

Infinite Loops

If a condition is always true, the loop becomes infinite. We can implement an infinite loop using a while statement:

object Test {
   def main(args: Array[String]) {
      var a = 10;
      // infinite loop
      while( true ){
         println( "a 的值为 : " + a );
      }
   }
}

After running the above code, the loop will execute forever; you can stop it with Ctrl + C.