| ////////////////////////////////////////// |
| |
| Licensed to the Apache Software Foundation (ASF) under one |
| or more contributor license agreements. See the NOTICE file |
| distributed with this work for additional information |
| regarding copyright ownership. The ASF licenses this file |
| to you under the Apache License, Version 2.0 (the |
| "License"); you may not use this file except in compliance |
| with the License. You may obtain a copy of the License at |
| |
| http://www.apache.org/licenses/LICENSE-2.0 |
| |
| Unless required by applicable law or agreed to in writing, |
| software distributed under the License is distributed on an |
| "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY |
| KIND, either express or implied. See the License for the |
| specific language governing permissions and limitations |
| under the License. |
| |
| ////////////////////////////////////////// |
| |
| = Template Method Pattern |
| |
| |
| The http://en.wikipedia.org/wiki/Template_method_pattern[Template Method Pattern] abstracts away the details of several algorithms. The generic part of an algorithm is contained within a base class. Particular implementation details are captured within base classes. The generic pattern of classes involved looks like this: |
| |
| image::assets/img/TemplateMethodClasses.gif[] |
| |
| == Example |
| |
| In this example, `Accumulator` captures the essence of the accumulation algorithm. The base classes `Sum` and `Product` provide particular customised ways to use the generic accumulation algorithm. |
| |
| [source,groovy] |
| ---- |
| include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=template_method_example,indent=0] |
| ---- |
| |
| The resulting output is: |
| |
| ---- |
| 10 |
| 24 |
| ---- |
| |
| In this particular case, you could use Groovy's inject method to achieve a similar result using Closures: |
| |
| [source,groovy] |
| ---- |
| include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=template_method_example2,indent=0] |
| ---- |
| |
| Thanks to duck-typing, this would also work with other objects which support an add (plus() in Groovy) method, e.g.: |
| |
| In this particular case, you could use Groovy's inject method to achieve a similar result using Closures: |
| |
| [source,groovy] |
| ---- |
| include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=template_method_example3,indent=0] |
| ---- |
| |
| We could also do the multiplication case as follows: |
| |
| [source,groovy] |
| ---- |
| include::{projectdir}/src/spec/test/DesignPatternsTest.groovy[tags=template_method_example4,indent=0] |
| ---- |
| |
| Using closures this way looks more like the <<_strategy_pattern,Strategy Pattern>> but if we realise that the built-in ++inject++ method is the generic part of the algorithm for our template method, then the Closures become the customised parts of the template method pattern. |