Prototype Builder Pattern

Code Examples

Prototype Builder from Object Instance

@Getter
@Builder
@ToString
public class Employee {
 
    private String name;
    private String description;
 
    public EmployeePrototypeBuilder toPrototypeBuilder() {
        var prototype = Employee.builder()
            .name(this.name)
            .description(this.description)
            .build();
        return new EmployeePrototypeBuilder(prototype);
    }
 
    public static class EmployeePrototypeBuilder {
        private Employee prototype;
        private String name;
        private boolean nameSet = false;
        private String description;
        private boolean descriptionSet = false;
 
        private EmployeePrototypeBuilder(Employee prototype) {
            this.prototype = prototype;
        }
  
        public EmployeePrototypeBuilder name(String name) {
            this.name = name;
            this.nameSet = true;
            return this;
        }
  
        public EmployeePrototypeBuilder description(String description) {
            this.description = description;
            this.descriptionSet = true;
            return this;
        }
 
        private void resetFlags() {
            this.nameSet = false;
            this.descriptionSet = false;
        }
  
        public Employee build() {
            var e = Employee.builder()
                .name(this.nameSet ? this.name : prototype.name)
                .description(this.descriptionSet ? this.description : prototype.description)
                .build();
            resetFlags();
            return e;
        }
    }
}

public class Main {
    public static void main(String[] args) {
        Employee employee = Employee.builder()
                                .name("default name")
                                .description("default description")
                                .build();
    
        EmployeePrototypeBuilder prototypeBuilder = employee.toPrototypeBuilder();
        Employee employee1 = prototypeBuilder.name("marcus").build();
        Employee employee2 = prototypeBuilder.build();

        System.out.println(employee1); // Employee(name=marcus, description=default description)
        System.out.println(employee2); // Employee(name=default name, description=default description)
    }
}

Prototype Builder from Builder Instance (BROKEN)

public interface Prototype<T> {
    T prototype();
}

public class Employee {
    private String name; 
    private String description;
 
	public static EmployeeBuilder builder() {
		return new EmployeeBuilder();
	}
 
    public static class EmployeeBuilder implements Prototype<EmployeeBuilder> {
        private String name;
        private String description;
 
        public EmployeeBuilder name(String name) {
            this.name = name;
            return this;
        }
 
        public EmployeeBuilder description(String description) {
            this.description = description;
            return this;
        }
 
        public EmployeeEmployee build() {
            Employee e = new Employee();
            e.name = this.name;
            e.description = this.description;
            return e;
        }
 
		@Override
		public EmployeeBuilder prototype() {
			Builder builder = new Builder();
			builder.name(name);
			builder.descrption(description);
			return builder;
		}
    }
}

public static void main(String[] args) {
	EmployeeBuilder baseBuilder = Employee.builder().description("default description");
 	Employee employee1 = baseBuilder.name("marcus").build();

	EmployeeBuilder prototypeBuilder1 = builder.prototype().description("default description 1");
	Employee employee1a = prototypeBuilder1.name("marcus").build();
 	Employee employee1b = prototypeBuilder1.name("marcus").build();

  	EmployeeBuilder prototypeBuilder2 = builder.prototype().description("default description 2");
 	Employee employee2a = prototypeBuilder2.name("marcus").build();
 	Employee employee2b = prototypeBuilder2.name("marcus").build();
}