Design Pattern - Builder Pattern

 https://howtodoinjava.com/design-patterns/creational/builder-pattern-in-java/#:~:text=The%20builder%20pattern%20is%20a,object%20it%20is%20to%20create.

In the above provided link you can acquire some notion about Builder Pattern. 

Here I provided one example of this pattern:

package Main;

public class Vehicle {
    private String engine;
    private int wheel;
    private int airbags; // optional parameter

    public String getEngine() {
        return engine;
    }

    public int getWheel() {
        return wheel;
    }

    public int getAirbags() {
        return airbags;
    }

    private Vehicle(VehicleBuilder builder) {
        this.engine = builder.engine;
        this.wheel = builder.wheel;
        this.airbags = builder.airbags;
    }

    public static class VehicleBuilder {
        private String engine;
        private int wheel;
        private int airbags;

        public VehicleBuilder(String engine, int wheel) {
            this.engine = engine;
            this.wheel = wheel;
        }

        public VehicleBuilder setAirbags(int airbags) {
            this.airbags = airbags;
            return this;
        }

        public Vehicle build() {
            return new Vehicle(this);
        }
    }
}
package Main;

public class Main {

    public static void main(String[] args) {
        Vehicle car = new Vehicle.VehicleBuilder("1500cc", 4).setAirbags(2).build();
        Vehicle bike = new Vehicle.VehicleBuilder("250cc", 2).build();
    }
}

*Now here another example of Builder Pattern. This time we allow user to set 
multiple parameters after creating object.

public class Person {
    private String name;
    private String surname;
    private int age;
    private String religion;

    public void setName(String name) {
        this.name = name;
    }

    public void setSurname(String surname) {
        this.surname = surname;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setReligion(String religion) {
        this.religion = religion;
    }

    public String getName() {
        return name;
    }

    public String getSurname() {
        return surname;
    }

    public int getAge() {
        return age;
    }

    public String getReligion() {
        return religion;
    }

    public static class PersonBuilder {
        private String name;
        private String surname;
        private int age;
        private String religion;

        public PersonBuilder(String name, String surname) {
            this.name = name;
            this.surname = surname;
        }

        public PersonBuilder setAge(int age) {
            this.age = age;
            return this;
        }

        public PersonBuilder setReligion(String religion) {
            this.religion = religion;
            return this;
        }

        public Person build() {
            return new Person(this);
        }
    }

    private Person(PersonBuilder builder) {
        this.name = builder.name;
        this.surname = builder.surname;
        this.age = builder.age;
        this.religion = builder.religion;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", surname='" + surname + '\'' +
                ", age=" + age +
                ", religion='" + religion + '\'' +
                '}';
    }
}

*Another alternative:
public class Fanar {
    private String name;
    private String surname;
    private String fatherName;
    private int age;

    private Fanar() {
    }

    private Fanar(String name, String surname, String fatherName, int age) {
        this.name = name;
        this.surname = surname;
        this.fatherName = fatherName;
        this.age = age;
    }

    public static class FanarBuilder {
        private Fanar f = null;

        public FanarBuilder() {
            f = new Fanar();
        }

        public FanarBuilder setName(String name) {
            this.f.name = name;
            return this;
        }

        public FanarBuilder setSurname(String surname) {
            this.f.surname = surname;
            return this;
        }

        public FanarBuilder setFatherName(String fatherName) {
            this.f.fatherName = fatherName;
            return this;
        }

        public FanarBuilder setAge(int age) {
            this.f.age = age;
            return this;
        }

        public Fanar build() {
            return new Fanar(f.name, f.surname, f.fatherName, f.age);
        }
    }

    @Override
    public String toString() {
        return "Fanar{" +
                "name='" + name + '\'' +
                ", surname='" + surname + '\'' +
                ", fatherName='" + fatherName + '\'' +
                ", age=" + age +
                '}';
    }
}

package com.company;

public class BMW {
    private String name;
    private String color;
    private String engine;

    private BMW() {
    }
    public String getName() {
        return name;
    }
    public String getColor() {
        return color;
    }
    public String getEngine() {
        return engine;
    }

    private static Builder builder;
    public static Builder builder() {
        if (builder == null) {
            builder = new Builder();
        }
        builder.bmw = new BMW();
        return builder;
    }

    public static class Builder {
        private BMW bmw;

        public Builder setName(String name) {
            bmw.name = name;
            return this;
        }

        public Builder setColor(String color) {
            bmw.color = color;
            return this;
        }

        public Builder setEngine(String engine) {
            bmw.engine = engine;
            return this;
        }

        public BMW build(){
            return bmw;
        }
    }
}

package com.company;

public class BMW {
    private String name;
    private String color;
    private String engine;

    private BMW() {
    }
    public String getName() {
        return name;
    }
    public String getColor() {
        return color;
    }
    public String getEngine() {
        return engine;
    }

    public static class Builder {
        private BMW bmw;
        private static Builder builder;
        public static Builder builder() {
            if (builder == null) {
                builder = new Builder();
            }
            builder.bmw = new BMW();
            return builder;
        }

        public Builder setName(String name) {
            bmw.name = name;
            return this;
        }

        public Builder setColor(String color) {
            bmw.color = color;
            return this;
        }

        public Builder setEngine(String engine) {
            bmw.engine = engine;
            return this;
        }

        public BMW build(){
            return bmw;
        }
    }
}

package com.builder;

public class User {
    private String name;
    private String surname;
    private String fatherName;
    
    public static class Builder{
        private User user;

        public Builder name(String name){
            user.name = name;
            return this;
        }

        public Builder surname(String surname){
            user.surname = surname;
            return this;
        }

        public Builder fatherName(String faherName){
            user.fatherName = faherName;
            return this;
        }

        public User build(){
            return user;
        }
    }
}

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