Loops

For loop

The for statement provides a compact way to iterate over a range of values.

The general form of the for statement can be expressed like this:

then{
   for (initialization; test; increment) {
       statements
   }
}

The expression initialization is used to initialize the loop. It is run once at the beginning of the loop. The test expression determines when to terminate the loop. This expression is evaluated at the top of each iteration of the loop. When the expression evaluates to false, the loop terminates. Finally, increment is an expression that is invoked after each iteration through the loop. Here is an example:

then {
   int ?i = 1;
   int ?j = 1;
   for ( ?i = 1; ?i <= 3; ?i++ ) {
      for ( ?j = 1; ?j <= 3; ?j++ ) {
         System.out.println(" i =" + ?i + " j = " + ?j ) ; 
      }
   }
}

Often for loops are used to iterate over the elements in an array, or the characters in a string. The following example uses a for statement to iterate over the elements of an array and print them:

then {
   for (?i = 0; ?i < ?arrayOfInts.length; ?i++) {
      System.out.println(?arrayOfInts[?i] + " ");
   }
}

While loop

You use a while statement to continually run a block of statements while a condition remains true. The general syntax of the while statement is:

then {
   while (test) {
       statements
   }
}

First the while statement evaluates the test expression, which must return a boolean value. If the test returns true, then the while statement runs the statements associated with it. The while statement continues testing the test expression and executing its block until the test returns false. Here is an example of a while loop:

then {
   int ?i = 0 ;
     while ( ?i <= 3 ) {
        System.out.println( ?i ) ;
        ?i++ ;
     }
}

The following example uses a while statement in the action part of the rule to iterate over an array of elements in a variable named elements. The variable elements is bound to an attribute of a variable c, also named elements. The variable c is declared in the condition part of the rule as a collection of ManagedObject().

rule foundManagedObject {
  when {
    ?c: collect ManagedObject();
  }
  then {
    Enumeration ?elements = ?c.elements();
    while (?elements.hasMoreElements()) {
     System.out.println(elements.nextElement());
    }
  }
}