Headline

Use of the Template design pattern in Java

Characteristics

We identify templates for queries and transformations over companies. We instantiate those templates for totaling and cutting salaries.

Illustration

The data model is implemented with object composition. For example Companies:

/**
 * A company has a name and consists of (possibly nested) departments.
 */
public class Company implements Serializable {

    private static final long serialVersionUID = -200889592677165250L;
    
    private String name;
    private List<Department> depts = new LinkedList<Department>();

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<Department> getDepts() {
        return depts;
    }

}

Feature:Closed serialization is implemented using Language:Java Technology:Object Streams:

    /*
     * Read (say, deserialize) a company.
     */
    public static Company deserializeCompany(String filename) {

        Object o = null;

        try {
            FileInputStream fis = new FileInputStream(filename);
            ObjectInputStream in = new ObjectInputStream(fis);
            o = in.readObject();
            in.close();
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        return (Company) o;
    }
    /*
     * Write (say, serialize) a company.
     */
    public static boolean serializeCompany(Company c, String filename) {

        FileOutputStream fos = null;
        ObjectOutputStream out = null;

        try {
            fos = new FileOutputStream(filename);
            out = new ObjectOutputStream(fos);
            out.writeObject(c);
            out.close();
            return true;
        } catch (IOException ex) {
            ex.printStackTrace();
            return false;
        }
    }

Feature:Total is implemented as a Reducer (query):

public class Total extends Reducer<Double> {

    @Override
    public Double zero() {
        return 0.0;
    }

    @Override
    public Double append(Double x, Double y) {
        return x+y;
    }

    @Override
    public Double visit(Employee e) {
        return e.getSalary();
    }

}

Feature:Cut is implemented as a Walker (transformation):

public class Cut extends Walker {
    public void visit(Employee e) {
        e.setSalary(e.getSalary() / 2.0);
    }

}

Test cases are implemented for all Namespace:Features.

Relationships

For basic OO without inheritance see Contribution:javaComposition.

For basic OO with inheritance see Contribution:javaInheritance.

For modular OO programming with static methods see Contribution:javaStatic.

For use of Java reflection see Contribution:javaReflection (data processing) and Contribution:javaSyb (SYB-style generic programming).

For design patterns see Contribution:javaTemplate (template design pattern), Contribution:javaVisitor (visitor design pattern) and Contribution:javaExorcism (excessive illustration of design patterns).

Architecture

The contribution follows a standardized structure:

  • inputs contains input files for tests
  • src/main/java contains the following packages:
    • org.softlang.company.features for implementations of Functional requirements.
    • org.softlang.company.features.template for query and transformation patterns.
    • org.softlang.company.model for implementations of Feature:Company.
  • src/test/java contains the following packages:

Usage

This contribution uses Technology:Gradle for building. Technology:Eclipse is supported.

See https://github.com/101companies/101simplejava/blob/master/README.md

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