patterns22TemplateMethodPattern

1package pkg8patterns;2 3/*4 * Template Method (Behavioral)5 * ----------------------------6 * INTENT: define the skeleton of an algorithm in a base method, deferring some7 *         steps to subclasses without changing the algorithm's structure.8 * UML: AbstractClass + templateMethod() (final) + step1()/step2() (abstract).9 * PROS: code reuse; enforce invariant algorithm structure ("Hollywood principle").10 * CONS: inheritance-based (less flexible than composition/strategy).11 * REAL-WORLD: java.util.AbstractList, InputStream.read, HttpServlet.service.12 */13public class patterns22TemplateMethodPattern {14 15    static abstract class DataProcessor {16        // The template method: fixed steps, variable implementations17        final void process() {18            read();19            transform();20            write();21        }22        abstract void read();23        abstract void transform();24        void write() { System.out.println("  writing result (default)"); }   // hook with default25    }26 27    static class CsvProcessor extends DataProcessor {28        void read() { System.out.println("CSV: read rows"); }29        void transform() { System.out.println("CSV: split by comma"); }30    }31    static class JsonProcessor extends DataProcessor {32        void read() { System.out.println("JSON: read document"); }33        void transform() { System.out.println("JSON: parse tree"); }34        @Override void write() { System.out.println("  JSON: pretty-print result"); }   // override hook35    }36 37    public static void main(String[] args) {38        System.out.println("-- CSV --"); new CsvProcessor().process();39        System.out.println("-- JSON --"); new JsonProcessor().process();40    }41}