FatnessChecker
This project is sample of dependency injection for Java.
If you want to see details, please see the 12th article of Java Advent Calendar 2018. (Japanese only)
Short Story: Obese Judgement
👨 I want to check my health. Let's ask the Fatness-Assessment-Company for inspection!
After several hours.
:person_frowning: Welcome to the Fatness-Assessment-Company. May I ask your height and weight?
👨 Well, my height is 170 cm, weight is 70 kg.
:person_frowning: Certainly. Please wait a moment. We will calculate your BMI with our latest type robot.
🤖 Now Calculating... 70 kg divided by 1.70 m equals 41.18, so the BMI is 41.18!
:person_frowning: OK, The BMI is over 40, so you are Obese (Level 4) in Japan.
👨 No way!
After several hours
👨 I'm definitely not obese. That robot must have been broken.
👴 Are you having trouble of Fatness-Assessment-Company? Let me hear your story if you do not mind.
👨 Yeah, Bla bla bla...
A few days later
💁 Welcome to the Fatness-Assessment-Company. May I ask your height and weight?
👨 Height is 170 cm, weight is 70 kg.
💁 Just a moment please. I will calculate the BMI with the robot.
👨 Wait! I want this person to calculate the BMI.
👴 Let me see, 70 kg divided by the square of 1.70 m equals 24.22, so his BMI is 24.22.
💁 Certainly. The BMI is over 18.5 and less than 25, so you are Normal Weight in Japan.
👨 I did it!
Role of the People
The people who appeared in this story are as follows.
- 👨 is a person who want to know his degree of obesity. We will call him
Userin this article. - :person_frowning: is a person who uses 🤖 to determine the degree of obesity. We will call her
FatnessCheckerin this article. - 🤖 is a robot that calculates BMI. There is still a bug. We will call it
BmiRobotin this article. - 👴 is an expert in calculating BMI. He definitely do not mistake the calculation. We will call him
BmiMasterin this article. - 💁 is a person who judges the degree of obesity by using 👴. :person_frowning: is same person, but to distinguish it for explanation, we will call her
FatnessCheckerDiin this article.
Problems of this case
🤖 BmiRobot has mistakenly calculated BMI. Apparently there seems to be a bug.
:person_frowning: FatnessChecker performed obesity degree judgment based on this incorrect calculation result, so the judgment result was also wrong.
In other words, it is a problem that :person_frowning: FatnessChecker depended on 🤖 BmiRobot with low reliability.
DI
👨 User asked 💁 FatnessCheckerDi to let 👴 BmiMaster calculate BMI, because he trust him.
This will enable that the judgment result of:information_desk_person: FatnessCheckerDi will depend on a reliable 👴 BmiMaster.
This is DI (dependency injection)! In other words,