Creational Patterns

• Defers part of object creation to another class
• Overview
  • Builder
  • Factory
  • Prototype

Two Recurring Themes of Creational Patterns

1. They encapsulate knowledge about which concrete classes the system uses
   • Abstracts the instantiation process
2. Hide how instances of classes are created and put together
   • Helps make a system independent of how its objects are created, composed, or represented

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Builder

Problem

• Separate the construction of a complex object from its representation so that the same construction process can create different representations

  Solution

• encapsulates the construction logic and provides methods to set different attributes or configurations of the object.

  Consequences

• improves the readability and maintainability of code by separating the construction logic from the object’s class, allowing for easy modification and extension of object construction processes.
• However, it may result in more code and complexity due to the additional builder class, and may not be suitable for simple object construction scenarios.

Brief Example

• Here, the LicenseBuilder is a builder of License objects.

public void demo() {
		License license = new LicenseBuilder()
            .setBirthDate(new Date()),
            .setName("John"),
            .setAddressLine1("123 Square Lane"),
            .setCity("Milford"),
            .setState("Delaware"),
            .setZipCode(19720);
            .setLicenseNumber(1238913312)
            .build();
}

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Factory

Problem

• Separate the construction of a complex object from its representation so that the same construction process can create different representations

Brief Example

• Here, the LicenseFactory leverages a LicenseBuilder to produce instances of License objects.

public class LicenseFactory {
  private LicenseBuilder builder;

  public LicenseFactory(LicenseBuilder builder) {
    this.builder = builder;
  }

  public License createLicense(String addressLine1, String addressLine2, String city, String state, String zipcode) {
      return builder
              .setAddressLine1(addressLine1)
              .setAddressLine2(addressLine2)
              .setCity(city)
              .setState(state)
              .setZipcode(zipcode)
              .createLicense();
  }
  public License createLicense(String firstName, String lastName, Date birthdate, Long licenseNumber) {
      return builder
              .setFirstName(firstName)
              .setLastName(lastName)
              .setBirthDate(birthdate)
              .setLicenseNumber(licenseNumber)
              .createLicense();
  }
}

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Prototype Design Pattern

Problem

• Need to create multiple instances of objects with similar properties and behavior.
• Want to avoid the overhead of creating new objects from scratch each time.
• Need a way to clone existing objects to create new objects with the same properties and behavior.

Solution

• Define a prototype object that serves as a template for creating new objects.
• Clone the prototype object to create new objects with the same properties and behavior.
• Use a copy or clone operation to create new objects instead of creating them from scratch.

Consequences

• Allows for efficient creation of new objects with similar properties and behavior.
• Reduces the need to instantiate objects from scratch, saving time and resources.
• Can improve performance and memory usage in situations where creating new objects is expensive.
• Provides flexibility in creating objects with different configurations or states based on the prototype object.
• May require careful handling of mutable objects to avoid unintended changes in cloned objects.

Brief Example

public class LicenseBuilder {
    private Date birthDate;
    private String firstName;
    private String lastName;
    private Long licenseNumber;
    private Character driverClass;
    private String addressLine1;
    private String addressLine2;
    private String city;
    private String state;
    private String zipcode;

    public LicenseBuilder(LicenseBuilder licenseBuilderToBeCloned) {
        this.firstName = licenseBuilderToBeCloned.firstName;
        this.lastName = licenseBuilderToBeCloned.lastName;
        this.birthDate = licenseBuilderToBeCloned.birthDate;
        this.licenseNumber = licenseBuilderToBeCloned.licenseNumber;
        this.driverClass = licenseBuilderToBeCloned.driverClass;
        this.addressLine1 = licenseBuilderToBeCloned.addressLine1;
        this.addressLine2 = licenseBuilderToBeCloned.addressLine2;
        this.city = licenseBuilderToBeCloned.city;
        this.state = licenseBuilderToBeCloned.state;
        this.zipcode = licenseBuilderToBeCloned.zipcode;
    }
}

Summary