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Factory method design pattern in java
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Factory method design pattern in java. .


Factory Method design pattern example in java?


Factory Method:-
The Factory Design Pattern or Factory Method Design Pattern is the creational design pattern. It is used to create Java Object based on the context/parameter.
Normally we create java object by using 'new' operator (e.g. A a = new A()). This is kind of hardcoding in the java functional code.
So we want to seperate object creation part from the code where we write business logic.
Factory method design pattern can be adopted to achieve it.
Factory method design pattern â??defines an interface/abstract class for creating an object, but let subclasses decide which class to instantiate(which object to create). The Factory method design pattern lets a class defer instantiation to its subclassesâ?. This pattern delegates the responsibility of initializing a class from the client to a particular factory class.
It has been used / implemented in the following classes of java.util package
  • java.util.Calendar#getInstance()
  • java.util.ResourceBundle#getBundle()
  • java.text.NumberFormat#getInstance()
Advantages:
  • Loose coupling. Delegating the responsibility of object creation part to factory classes.
  • The life-cycle management of the objects should be centralized to make sure a consistent behavior in a application and Factory method design pattern provides that.
  • Iit can return the same object multiple times. Or can return a subclass rather than an object of that exact type.
  • The new operator is kind of hard-coding. There is a difference between requesting an object instead of creating one. The new operator always creates an object, and does not encapsulate object creation. A Factory Method does that encapsulation and allows an object to be requested .
Example:
package test.easycodeforall.factorymethod;

public abstract class Employee {
	public abstract Double getSalary();

}
------------

package test.easycodeforall.factorymethod;

public class ContractEmployee extends Employee {
	@Override
	public Double getSalary() {
		return 1000.00;
	}
}
------------

package test.easycodeforall.factorymethod;

public class PermanentEmployee extends Employee {
	@Override
	public Double getSalary() {
		return 2000.00;
	}
}
------------
		
package test.easycodeforall.factorymethod;

public abstract class EmployeeFactory {
	public abstract Employee creageEmployeeObj();
}
------------

package test.easycodeforall.factorymethod;

public class ContractEmployeeFactory extends EmployeeFactory {
	@Override
	public Employee creageEmployeeObj() {
		return new ContractEmployee();
	}
}

------------
package test.easycodeforall.factorymethod;

public class PermanentEmployeeFactory extends EmployeeFactory {
	@Override
	public Employee creageEmployeeObj() {
		return new PermanentEmployee();
	}
}
------------
		
		
 
package test.easycodeforall.factorymethod;

public class ObjectCreator {
	public static Employee getEmployee(EmployeeFactory factory) {
		return factory.creageEmployeeObj();
	}
}
 
package test.easycodeforall.factorymethod;

public class TestFactoryMethod {
	public static String DEFAULT_EMPLOYEE_TYPE = "CONTRACTOR";

	public static void main(String[] args) {
		String employeeType = System.getProperty("employeeType");
		if (employeeType == null)
			employeeType = DEFAULT_EMPLOYEE_TYPE;
		EmployeeFactory factory = null;

		if ("CONTRACTOR".equals(employeeType)) {
			factory = new ContractEmployeeFactory();
		} else {
			factory = new PermanentEmployeeFactory();
		}

		Employee emp = ObjectCreator.getEmployee(factory);
		emp.getSalary();
	}

}



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