When a class requires more arguments to instantiate then it is better to go for a builder pattern. Let me explain with an example.
For example, you are developing an application to maintain all the employees’ information of organization ‘ABC’. Initially, I designed Employee model class like below.
Approach 1: Design Employee model class by providing setter and getter methods.
Employee.java
public class Employee {
private int id;
private String firstName;
private String lastName;
private float salary;
private String designation;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public float getSalary() {
return salary;
}
public void setSalary(float salary) {
this.salary = salary;
}
public String getDesignation() {
return designation;
}
public void setDesignation(String designation) {
this.designation = designation;
}
}
There is a problem with this approach. Since Employee class provides setter methods, you can’t make the Employee class immutable.
Approach 2: We can make the class ‘Employee’ immutable, by not providing setter methods and providing different combinations of constructors to initialize instance properties.
Employee.java
public class Employee {
private int id;
private String firstName;
private String lastName;
private float salary;
private String designation;
private static final String DEFAULT_NAME = "no_name";
private static final int DEFAULT_ID = -1;
private static final String DEFAULT_DESIGNATION = "Engineer";
private static final float DEFAULT_SALARY = 25000;
public Employee() {
this(DEFAULT_ID, DEFAULT_NAME, DEFAULT_NAME, DEFAULT_SALARY, DEFAULT_DESIGNATION);
}
public Employee(int id) {
this(id, DEFAULT_NAME, DEFAULT_NAME, DEFAULT_SALARY, DEFAULT_DESIGNATION);
}
public Employee(int id, String firstName) {
this(id, firstName, DEFAULT_NAME, DEFAULT_SALARY, DEFAULT_DESIGNATION);
}
public Employee(int id, String firstName, String lastName) {
this(id, firstName, lastName, DEFAULT_SALARY, DEFAULT_DESIGNATION);
}
public Employee(int id, String firstName, String lastName, float salary, String designation) {
this.id = id;
this.firstName = firstName;
this.lastName = lastName;
this.salary = salary;
this.designation = designation;
}
public int getId() {
return id;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public float getSalary() {
return salary;
}
public String getDesignation() {
return designation;
}
}
There is a problem with above model class, As you see the definition of Employee class, I provided 4 different constructors to initialize different combination of properties. What if my class has more instance properties, I will end up in more and more constructor definitions, which is not feasible. We can solve both the problems by providing builder object.
Approach 3: Define Employee model class using builder pattern.
Employee.java
public class Employee {
private int id;
private String firstName;
private String lastName;
private float salary;
private String designation;
private Employee() {
}
public int getId() {
return id;
}
public String getFirstName() {
return firstName;
}
public String getLastName() {
return lastName;
}
public float getSalary() {
return salary;
}
public String getDesignation() {
return designation;
}
public static class EmployeeBuilder {
private static final String DEFAULT_NAME = "no_name";
private static final int DEFAULT_ID = -1;
private static final String DEFAULT_DESIGNATION = "Engineer";
private static final float DEFAULT_SALARY = 25000;
private int id;
private String firstName;
private String lastName;
private float salary;
private String designation;
public EmployeeBuilder() {
this.id = DEFAULT_ID;
this.firstName = this.lastName = DEFAULT_NAME;
this.salary = DEFAULT_SALARY;
this.designation = DEFAULT_DESIGNATION;
}
public EmployeeBuilder id(int id) {
this.id = id;
return this;
}
public EmployeeBuilder firstName(String firstName) {
this.firstName = firstName;
return this;
}
public EmployeeBuilder lastName(String lastName) {
this.lastName = lastName;
return this;
}
public EmployeeBuilder salary(float salary) {
this.salary = salary;
return this;
}
public EmployeeBuilder designation(String designation) {
this.designation = designation;
return this;
}
public Employee build() {
Employee emp = new Employee();
emp.designation = this.designation;
emp.firstName = this.firstName;
emp.id = this.id;
emp.lastName = lastName;
emp.salary = salary;
return emp;
}
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder();
builder.append("Employee [id=").append(id).append(", firstName=").append(firstName).append(", lastName=")
.append(lastName).append(", salary=").append(salary).append(", designation=").append(designation)
.append("]");
return builder.toString();
}
}
Test.java
public class Test {
public static void main(String args[]) {
Employee.EmployeeBuilder builder = new Employee.EmployeeBuilder();
Employee emp = builder.id(553)
.firstName("Hari krishna")
.lastName("Gurram")
.designation("Software Engineer")
.build();
System.out.println(emp);
}
}
Output
Employee [id=553, firstName=Hari krishna, lastName=Gurram, salary=25000.0, designation=Software Engineer]
In real world applications, it is always good coding practice to code for an interface. For example, you can define a Builder interface like below, and make the EmployeeBuilder class implements the Builder interface.
public interface BuilderT> {
public T build();
}
Implement EmployeeBuilder like below.
public static class EmployeeBuilder implements BuilderEmployee> {
private static final String DEFAULT_NAME = "no_name";
private static final int DEFAULT_ID = -1;
private static final String DEFAULT_DESIGNATION = "Engineer";
private static final float DEFAULT_SALARY = 25000;
private int id;
private String firstName;
private String lastName;
private float salary;
private String designation;
public EmployeeBuilder() {
this.id = DEFAULT_ID;
this.firstName = this.lastName = DEFAULT_NAME;
this.salary = DEFAULT_SALARY;
this.designation = DEFAULT_DESIGNATION;
}
public EmployeeBuilder id(int id) {
this.id = id;
return this;
}
public EmployeeBuilder firstName(String firstName) {
this.firstName = firstName;
return this;
}
public EmployeeBuilder lastName(String lastName) {
this.lastName = lastName;
return this;
}
public EmployeeBuilder salary(float salary) {
this.salary = salary;
return this;
}
public EmployeeBuilder designation(String designation) {
this.designation = designation;
return this;
}
@Override
public Employee build() {
Employee emp = new Employee();
emp.designation = this.designation;
emp.firstName = this.firstName;
emp.id = this.id;
emp.lastName = lastName;
emp.salary = salary;
return emp;
}
}
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