Dezign Patterns

Prototype Design Pattern

The Prototype Pattern is used to create new objects by copying an existing object, which is referred to as a prototype.

Let's take an example of template , which is used across the Organization.

Everytime we create a report , we use the template and fill the data.

Template Reuse: Styles and formats are reused without recreating them every time.
Performance: No need to reapply formatting logic on each report.
Consistency: Ensures reports follow an organization-wide standard.

Example


I - Prototype Interface

public abstract class ExcelReport implements Cloneable {
    protected String headerStyle;
    protected String cellStyle;
    protected String footer;

    public abstract void fillData(String[][] data);
    public abstract void export(String filename);

    @Override
    public ExcelReport clone() {
        try {
            return (ExcelReport) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException("Cloning not supported", e);
        }
    }
}

II - Concrete Template

public class StandardExcelReport extends ExcelReport {

    private String[][] data;

    public StandardExcelReport() {
        this.headerStyle = "Bold | Blue Background";
        this.cellStyle = "Bordered | Font: Calibri 11";
        this.footer = "Confidential © 2025";
        this.data = new String[0][];
    }

    @Override
    public void fillData(String[][] data) {
        this.data = data;
    }

    @Override
    public void export(String filename) {
        System.out.println("Exporting Report: " + filename);
        System.out.println("Header Style: " + headerStyle);
        System.out.println("Cell Style: " + cellStyle);
        System.out.println("Footer: " + footer);
        System.out.println("Data:");
        for (String[] row : data) {
            for (String cell : row) {
                System.out.print(cell + " | ");
            }
            System.out.println();
        }
        System.out.println("File saved as " + filename + "
");
    }
}

III - Prototype Cache

import java.util.HashMap;
import java.util.Map;

public class ReportManager {
    private Map<String, ExcelReport> templates = new HashMap<>();

    public void addTemplate(String key, ExcelReport report) {
        templates.put(key, report);
    }

    public ExcelReport getClonedReport(String key) {
        ExcelReport template = templates.get(key);
        return template != null ? template.clone() : null;
    }
}


IV - Client Code

public class ExcelPrototypeDemo {
    public static void main(String[] args) {
        // Initialize template
        ReportManager manager = new ReportManager();
        ExcelReport standardTemplate = new StandardExcelReport();
        manager.addTemplate("standard", standardTemplate);

        // Clone and use for Report 1
        ExcelReport report1 = manager.getClonedReport("standard");
        report1.fillData(new String[][] {
            {"Name", "Sales", "Region"},
            {"Alice", "5000", "East"},
            {"Bob", "7000", "West"}
        });
        report1.export("SalesReport_Q1.xlsx");

        // Clone and use for Report 2
        ExcelReport report2 = manager.getClonedReport("standard");
        report2.fillData(new String[][] {
            {"Name", "Hours", "Project"},
            {"John", "40", "Alpha"},
            {"Doe", "35", "Beta"}
        });
        report2.export("Timesheet_May.xlsx");
    }
}