Automatic Refactoring to Builder Pattern in Java

Large constructors suck! With IntelliJ IDEA, you can automagically refactor the large constructor to a builder.

Here is an example. Consider this Device class:

class Device {
    private UUID deviceId;
    private String name;
    private boolean status;
    private LocalDateTime startDateTime;
    private double generatedPower;

    public Device(UUID deviceId, String name, boolean status,
                  LocalDateTime startDateTime, double generatedPower) {
        this.deviceId = deviceId;
        this.name = name;
        this.status = status;
        this.startDateTime = startDateTime;
        this.generatedPower = generatedPower;
    }

    @Override
    public String toString() {
        return "Device{" +
                "deviceId=" + deviceId +
                ", name='" + name + '\'' +
                ", status=" + status +
                ", startDateTime=" + startDateTime +
                ", generatedPower=" + generatedPower +
                '}';
    }
}

There are five fields and that makes the constructor parameter list long. When you create an object, the problem is obvious:

var device = new Device(UUID.randomUUID(), "FSF11", false, LocalDateTime.now(), 0);

We are already lost with what is false here and what is 0!

Fortunately, refactoring it is quite easy — what you need to do is select Refactor and Select the option to convert the constructor to a Builder class.

This results in this code:

import java.time.LocalDateTime;
import java.util.UUID;

public class DeviceBuilder {
    private UUID deviceId;
    private String name;
    private boolean status;
    private LocalDateTime startDateTime;
    private double generatedPower;

    public DeviceBuilder setDeviceId(UUID deviceId) {
        this.deviceId = deviceId;
        return this;
    }

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

    public DeviceBuilder setStatus(boolean status) {
        this.status = status;
        return this;
    }

    public DeviceBuilder setStartDateTime(LocalDateTime startDateTime) {
        this.startDateTime = startDateTime;
        return this;
    }

    public DeviceBuilder setGeneratedPower(double generatedPower) {
        this.generatedPower = generatedPower;
        return this;
    }

    public Device createDevice() {
        return new Device(deviceId, name, status, startDateTime, generatedPower);
    }
}

Now you go back and check your code that was creating a Device object using constructor, it would be automagically converted to using the DeviceBuilder class!

var device = new DeviceBuilder().setDeviceId(UUID.randomUUID())
                                .setName("FSF11")
                                .setStatus(false)
                                .setStartDateTime(LocalDateTime.now())
                                .setGeneratedPower(0)
                                .createDevice();

That’s much more readable and better, isn’t it?!

You can check this YouTube video that shows this refactoring visually here: https://youtu.be/fmoS15bnwBk