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A Groovy script is a sequence of statements:

When defining classes, we can provide 'asType' methods to convert the class into another using the 'as' operator. Classes we've seen in previous tutorials that convert to another using 'as' (eg, Integer, BigDecimal, String) use the 'asType' method under the hood:

We can use 'as' to convert a list into a class instance using the list elements as constructor arguments:

Conditional Statements

The if and if-else statements let us choose subsequent statements to execute based on a condition:

The meaning of the 'in' operator depends whether its context in the code is conditional or iterative. When in a conditional context, the 'isCase' method of the target is invoked:

The switch statement inspects an expression and resumes execution from the first matching case-expression, ie, regex matched, list or set or range contained in, class an instance of, or object equal to:

When we supply our own values in the case-expression, the 'isCase' method is invoked to determine whether or not the switch-expression is matched. If there's no 'isCase' method, the 'equals' method is used to test for equality:

Iterative Statements

The while statement lets us iterate through a block of code:

We've already seen the 'each' and other related method calls, which emulate the while-statement at a higher level of abstraction, but with some restrictions: the loop variable isn't available outside the loop, no guarantees are made about the order of iteration through the collection, and the 'break', 'continue', and 'return' commands aren't available:

Other method calls that loop are 'times', 'upto', 'downto', and 'step'. Like 'each', they don't allow 'break', 'continue', and 'return' commands, but do make guarantees about the order of iteration:

We can label any statement with a name. Labelling a while loop lets any arbitrarily deep nested statement break out of or continue on from it:


For-statements are complex yet powerful iterative statements with many possible formats. When 'in' is used in the iterative context of a for-statement, the 'iterator' method of the target is invoked. The 'iterator' method must return an Iterator, defining at least the 'hasNext' and 'next' methods:

The for-statement works with many kinds of objects (eg, Collection, array, Map, String, regex, File, Reader, InputStream, etc):

We can use 'break' and 'continue' within a for-loop using 'in':

'each' methods can also be considered as emulating for-loops at a higher level of abstraction, without the guarantees about the order of iteration, and the 'break', 'continue', and 'return' commands being unavailable:

Another format for the for-statement is the initializer-condition-incrementer format:

We can have more than one initializer, and more than one incrementer:

Operator Overloading

The precedence heirarchy of the operators, some of which we haven't looked at yet, is, from highest to lowest:

We've seen how the 'as' operator is mapped to the asType() method, and how the 'in' operator is mapped to the isCase() and iterator() methods. Many more operators have equivalent method names. We've seen how [] subscripting has equivalent methods getAt() and putAt() in the HashMap class. They are also equivalent when we define such methods on our own classes:

We've also seen how various operators have equivalent method names in the numerical classes, such as Integer, BigDecimal, float, etc. They, too, are also equivalent when we define such methods on our own classes:

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