Consider the following model:

class Student {
     private int id;
     private Boolean isPresent = Boolean.False;
}

Now if I build a student object using Builder pattern, while not setting the value for isPresent is 'null' and not 'false' as we have initialized.

Student model = Student.builder().id(10).build();
// model.isPresent is set as null instead of false 

I want to know for this particular use case is there any way to set isPresent to false i.e initialize a Boolean variable when user does not sets the value in Builder pattern? Please note I am unable to use boolean instead of 'Boolean' or set value of isPresent in builder.

Edit: I am using Lombok to implement builder pattern. I am using All args constructor and no args constructor and getter, setter methods.

CodePudding user response：

I'm a bit confused about which of the two approaches you are using, so I am providing answer for both the below cases:

1. Are you implementing the Builder Pattern?
2. Are you using any framework which provides the builder pattern for you?

1. If you are implementing the builder pattern you can initialize inside the StudentBuilder class this way:

class Student {
    private final int id;
    private Boolean isPresent = Boolean.FALSE;

    Student(int id, Boolean isPresent) {
        this.id = id;
        this.isPresent = isPresent;
    }

    public static StudentBuilder builder() {
        return new StudentBuilder();
    }

    public static class StudentBuilder {
        private int id;
        private Boolean isPresent = Boolean.FALSE;

        StudentBuilder() {
        }

        public StudentBuilder id(int id) {
            this.id = id;
            return this;
        }

        public StudentBuilder isPresent(Boolean isPresent) {
            this.isPresent = isPresent;
            return this;
        }

        public Student build() {
            return new Student(id, isPresent);
        }

        public String toString() {
            return "Student.StudentBuilder(id="   this.id   ", isPresent="   this.isPresent   ")";
        }
    }

2. if you are using any framework like Lombok for the builder pattern,

   You can replace the Boxed data type with primitive data types:

   class Student {
       private int id;
       private boolean isPresent;  //default is false.
   }
   

   That will also result in the false

Edit: Alternatively you can check for Null in the constructor and implement the logic by yourself.

Like:

@Getter
@Builder
class Student {
    private int id;
    private Boolean isPresent;

    private Student(int id, Boolean isPresent) {
        this.id = id;
        this.isPresent = isPresent;
        if (this.isPresent == null) {
            this.isPresent = false;
        }    
}

Note: When using the builder pattern you want to make the object as immutable after the build. So don't make the setter explicitly available, furthermore don't even allow the instantiation (make the constructor private).