Builder design pattern in java with example program

Posted by: Instanceofjava Posted date: August 23, 2016 / comment : 0 java design pattern interview questions and answers , java programming interview questions

• Design patterns are solutions to software design problems.
• Design patterns classified into three types.
• Creational, Structural and behavioral design patterns.


• Creational patterns helps us to create objects in a manner suitable to the given situation.
• Builder design pattern is one of the creational  design pattern in java.
• Builder  design pattern helps us to create complex class object.
• Builder design pattern helps us to separate the construction process of a complex object from its representation so that same object construction process can be created in different representations.
• Means it will separate complex construction into two parts  initialization of class instance and return  class instance.
• When a class having more number of fields and constructor of that class take care of assigning initial values. 
• And when we want to create object of the class we need to pass all  parameters and should be in same order which constructor is accepting.
• Builder design pattern helps us to create same class object by passing required number of fields by using separate builder class object.
• Builder design pattern is useful when object creation is very complex.

Advantages of builder design pattern:

• Builder design pattern simplifies complex object creation.
• Builder design pattern provides separation between instance creation and representation
• Re usability

 Program #1: Builder design pattern in java with example program

Employee:

1. package com.designpatternsinjava.builderdesignpattern;
2. 
   
3. public class Employee {
4. 
   
5. String name;
6. String company;
7. int id;
8. String passport_number;
9. String temp_address;
10. String perm_address;
11. int salary;
12. 
    
13. Employee(String name,String company,int id,String passport_number,String
14. temp_address,String perm_address,int salary){
15. this.name=name;
16. this.company=company;
17. this.id=id;
18. this.passport_number=passport_number;
19. this.temp_address=temp_address;
20. this.perm_address=perm_address;
21. this.salary=salary;
23. }
24. 
    
26. public String toString(){
28.  return "Name="+name+" \n Company="+company+"\n id="+id+"\n
29.    passport_number="+passport_number+"" +"\n temp_address="+temp_address+"\n
30.    perm_address"+perm_address+"\n
31.    salary="+salary;
33. 
    
34. }
37. }

EmployeeBuilder

1. package com.designpatternsinjava.builderdesignpattern;
2. 
   
3. public class EmployeeBuilder {
4. 
   
5. 
   
6. String name;
7. String company;
8. int id;
9. String passport_number;
10. String temp_address;
11. String perm_address;
12. int salary;
14. public EmployeeBuilder setName(String name) {
15. this.name = name;
16. return this;
17. }
18. 
    
19. public EmployeeBuilder setCompany(String company) {
20. this.company = company;
21. return this;
22. }
23. 
    
24. public EmployeeBuilder setId(int id) {
25. this.id = id;
26. return this;
27. }
28. 
    
29. public EmployeeBuilder setPassport_number(String passport_number) {
30. this.passport_number = passport_number;
31. return this;
32. }
33. 
    
34. public EmployeeBuilder setTemp_address(String temp_address) {
35. this.temp_address = temp_address;
36. return this;
37. }
38. 
    
39. public EmployeeBuilder setPerm_address(String perm_address) {
40. this.perm_address = perm_address;
41. return this;
42. }
43. 
    
44. public EmployeeBuilder setSalary(int salary) {
45. this.salary = salary;
46. return this;
47. }
50. public Employee build(){
51. return new Employee(name, company, id, passport_number, temp_address,
52. perm_address, salary);
53. }
54. 
    
55. }

BuilderDemo

• To create object of employee class  we need to provide all the fields values to the constructor.
• So it is somewhat difficult to pass all values all times.
• Employee builder class taken all variables of Employee and in setter methods accepts a value and returns EmployeBuilder object.
• And EmployeBuilder class has build method which will  assign all values to employee and returns Employee object.
• Employee empobj= new EmployeeBuilder().setName("Saidesh").setId(1234).build();
• Now we create object of Employee class by creating EmployeBuilder class object and caling calling setter methods whatever we have.
• Is is very easy to set the values because we have corresponding setter method name is same as variable name.
• After setting the values we need  to call build method so that it will return employee object with values.