Groovy Goodness: Remove Last Item From List Using RemoveLast Method (And Pop/Push Methods Reimplemented)

Versions of Groovy before 2.5.0 implemented pop and push methods for the List class for items at the end of a List object. The pop method removed the last item of a List and push added a item to the List. Groovy 2.5.0 reimplemented the methods so they now work on the first item of a List instance. To remove an item from the end of the list we can use the newly added method removeLast.

In the following example Groovy code we use the removeLast and add methods to remove and add items to the end of the list. And with the pop and push methods we remove and add items to the beginnen of the list:

Written with Groovy 2.5.0.

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Groovy Goodness: Getting All Init And Tail Values Recursively

For a long time we could get the tail or init values for a collection. Groovy 2.5.0 adds the methods inits and tails for Iterable objects. These methods return a List with List values where the first element is the original collection and the next is the result of init or tail on the previous element. This is repeated until the result of init or tail is an empty List.

In the next example script we have a original collection of letters. We first run the init and tail methods (without the s). Next we look at the result of invoking inits and tails:

Written with Groovy 2.5.0.

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Groovy Goodness: Truncate And Round BigDecimal Values

Groovy 2.5.0 adds round and truncate methods to the BigDecimal class. These methods were already available on Double and Float classes. The methods can take an argument to denote the number of decimals the rounding or truncating must be applied to.

In the following example we see the methods with and without arguments:

Written with Groovy 2.5.0.

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Groovy Goodness: Intersect Collections With Custom Comparator

In a previous post we learned about the intersect method added to collections in Groovy. Since Groovy 2.5.0 we can supply a custom Comparator to the intersect method to define our own rules for the intersection.

In the following example we first apply the intersect method with the default Comparator. Then we create a new Comparator using a closure where we check if the value is in both collections and if the value starts with the letter M:

Written with Groovy 2.5.0.

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Groovy Goodness: Easy Object Creation With Tap Method

Groovy 2.5.0 adds the tap method to all objects and changes the method signature of the with method. In a previous post we already learned about the with method. In Groovy 2.5.0 we can add an extra boolean argument to the with method. If the value is false (is default) the with method must return the same value as what the closure invocation returns. If the value is true the object instance on which the with method is invoked is returned. The new tap method is an alias for with(true), so it will always return the object instance.

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Groovy Goodness: Where Is My Class?

Groovy 2.5.0 makes it possible to get the location of a Class file by adding the method getLocation to the Class class. If the Class is part of the JDK the location returned is null, but otherwise we get the location of the JAR file or source file (if available) with the Class file.

In the following example we get the location for the internal JDK String class and the Groovy utility class ConfigSlurper:

Written with Groovy 2.5.0.

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Groovy Goodness: Calculate MD5 And SHA Hash Values

Groovy adds a lot of useful methods to the String class. Since Groovy 2.5.0 we can even calculate MD5 and SHA hash values using the methods md5 and digest. The md5 method create a hash value using the MD5 algorithm. The digest method accepts the name of the algorithm as value. These values are dependent on the available algorithms on our Java platform. For example the algorithms MD2, MD5, SHA-1, SHA-256, SHA-384 and SHA-512 are by default available.

In the next example we use the md5 and digest methods on a String value:

Written with Groovy 2.5.0.

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Groovy Goodness: Java 8 Stream Enhancements

Groovy 2.5.0 adds several methods to make working with Java 8 Streams more Groovy. First of all the methods toList and toSet are added to the Stream class. These methods will convert the stream to a List and Set using the Stream.collect method with Collectors.toList and Collectors.toSet as argument. Furthermore we can convert any array object to a Stream using the stream method that is added to all array objects.

In the following example we use the support of converting an array to a Stream and then getting a List and Set from the stream:

Written with Groovy 2.5.0.

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Groovy Goodness: Use Optional In Conditional Context

In Groovy 2.5.0 we can use a Java 8 Optional object in a conditional context. When an Optional object has a value the value is coerced to true and when empty the value is false.

Written with Groovy 2.5.0.

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Groovy Goodness: Using String Values In Ranges

We can use ranges in Groovy using an easy syntax where the start and end values of the range are separated by .. for an inclusive range and ..< for an exclusive range as we have seen in a previous post. The values of the range are mostly numbers or enum values. But we can also use String values to define a range. Groovy will check if the String values are the same length and if the values, except for the last character, are the same. Then the natural ordering of the last character of the String value, based on the character’s int value, is used to create the range values.

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