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Java Builder Pattern

Updated on January 27, 2013

Whether you are a beginner or an experienced Java programmer, you have probably already managed to write factories or builders to create your objects inside your applications. In this article I want to show you a smart method to build objects in Java in a flexible way using the Build Pattern. Start with this simple "User" object:

public class User {  
     private String firstName;  
     private String middleName;  
     private String surname;  
     private String email;  
     private String password;  
     public String getFirstName() {  
         return firstName;  
     }  
     public void setFirstName(String firstName) {  
         this.firstName = firstName;  
     }  
     public String getMiddleName() {  
         return middleName;  
     }  
     public void setMiddleName(String middleName) {  
         this.middleName = middleName;  
     }  
     public String getSurname() {  
         return surname;  
     }  
     public void setSurname(String surname) {  
         this.surname = surname;  
     }  
     public String getEmail() {  
         return email;  
     }  
     public void setEmail(String email) {  
         this.email = email;  
     }  
     public String getPassword() {  
         return password;  
     }  
     public void setPassword(String password) {  
         this.password = password;  
     }  
}

Now we need to build different instances of the same object (or working in a flexible way with the same instance). These instances can be created with a chain of constructors or methods (in this simple case it doesn't make a real difference which you use). Depending on which parameters are passed to build the object, you could end up seeing the following:

public class UserBuilder {  
     public User createUser(String firstName, String middleName, String surname) {  
         User user = new User();  
         user.setFirstName(firstName);  
         user.setMiddleName(middleName);  
         user.setSurname(surname);  
         return user;  
     }  
     public User createUser(String firstName, String middleName, String surname, String password) {  
         User user = createUser(firstName, middleName, surname);  
         user.setPassword(password);  
         return user;  
     }  
     public User createUser(String firstName, String middleName, String surname, String password, String email) {  
         User user = createUser(firstName, middleName, surname, password);  
         user.setEmail(email);  
         return user;  
     }  
 // etc  
}

What is the problem with the above? The more properties you have, the more methods you need to create and then flexibility is lost. Imagine you need an object that requires only firstName and password to be set. You need to add a new method that sets them, and so on for every different object setting. In this way covering all the possible combinations will be a real nightmare especially with objects that have 3, 4 or more properties. The same problem of course exists with the chain of constructors. Now I'll show you a possible solution for this kind of problem:

public class UserBuilder {   
    private User user;   

    public UserBuilder() {
      this.user = new User();
    }

    public UserBuilder withFirstName(String firstName) {   
      user.setFirstName(firstName);   
      return this;   
    }   

    public UserBuilder withMiddleName(String middleName) {   
      user.setMiddleName(middleName);   
      return this;   
    }   

    public UserBuilder withSurname(String surname) {   
      user.setSurname(surname);   
      return this;   
    }   

    public UserBuilder withEmail(String email) {   
      user.setEmail(email);   
      return this;   
    }   

    public UserBuilder withPassword(String password) {   
      user.setPassword(password);   
      return this;   
    }   

    public User build() {  
       return user;  
    }  
}   

This class offers you a simple, more readable and flexible way to build itself. How? Just look at this:

new UserBuilder().withFirstName("John").withMiddleName("The Slim").withSurname("Doe").build();  
 new UserBuilder().withFirstName("John").withMiddleName("The Slim").withEmail("myemail@somewhere.com").build();  
 new UserBuilder().withFirstName("John").withSurname("Doe").withPassword("secret").build();  
 new UserBuilder().withSurname("John").withEmail("myemail@somewhere.com").withPassword("secret").build();  
 // and so on...  

As you can see you don't need complex methods to build objects anymore and the readibility is much better than simple "create" methods. Have fun!

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