01-RED.java

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
  }
}

class QuestionList {
  public QuestionList() {
  }

  public String toJson() {
    return "";
  }
}

02-GREEN.java

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
  }
}

class QuestionList {
  public QuestionList() {
  }

  public String toJson() {
    return "[]";
  }
}

03-RED.java

import java.util.Arrays;
import java.util.List;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
  }
}

class QuestionList {
  private Question question;

  public QuestionList() {
  }

  public QuestionList(Question question) {
    this.question = question;
  }

  public String toJson() {
    return "[]";
  }
}

class Question {
  public Question(String body, List<String> answers) {

  }
}

04-GREEN.java

import java.util.Arrays;
import java.util.List;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
  }
}

class QuestionList {
  private Question question;

  public QuestionList() {
  }

  public QuestionList(Question question) {
    this.question = question;
  }

  public String toJson() {
    return question == null ? "[]" : "[{\"body\": \"body\", \"answers\": []}]";
  }
}

class Question {
  public Question(String body, List<String> answers) {

  }
}

05-RED.java

import java.util.Arrays;
import java.util.List;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
  }
}

class QuestionList {
  private Question question;

  public QuestionList() {
  }

  public QuestionList(Question question) {
    this.question = question;
  }

  public String toJson() {
    return question == null ? "[]" : "[{\"body\": \"body\", \"answers\": []}]";
  }
}

class Question {
  public Question(String body, List<String> answers) {
    
  }
}

06-GREEN.java

import java.util.Arrays;
import java.util.List;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
  }
}

class QuestionList {
  private Question question;

  public QuestionList() {
  }

  public QuestionList(Question question) {
    this.question = question;
  }

  public String toJson() {
    return question == null ? "[]" : "[{\"body\": \"" + question.getBody() + "\", \"answers\": []}]";
  }
}

class Question {
  private String body;

  public Question(String body, List<String> answers) {
    this.body = body;
  }

  public String getBody() {
    return body;
  }
}

07-REFACTORING.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
  }
}

class QuestionList {
  private Optional<Question> questionOpt;

  public QuestionList() {
    questionOpt = Optional.empty();
  }

  public QuestionList(Question question) {
    this.questionOpt = Optional.ofNullable(question);
  }

  public String toJson() {
    return questionOpt.map(question -> "[{\"body\": \"" + question.getBody() + "\", \"answers\": []}]")
        .orElseGet(() -> "[]");
  }
}

class Question {
  private String body;

  public Question(String body, List<String> answers) {
    this.body = body;
  }

  public String getBody() {
    return body;
  }
}

08-RED.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1"))).toJson()
        .equals("[{\"body\": \"body\", \"answers\": [\"answer1\"]}]"));
  }
}

class QuestionList {
  private Optional<Question> questionOpt;

  public QuestionList() {
    questionOpt = Optional.empty();
  }

  public QuestionList(Question question) {
    this.questionOpt = Optional.ofNullable(question);
  }

  public String toJson() {
    return questionOpt.map(question -> "[{\"body\": \"" + question.getBody() + "\", \"answers\": []}]")
        .orElseGet(() -> "[]");
  }
}

class Question {
  private String body;

  public Question(String body, List<String> answers) {
    this.body = body;
  }

  public String getBody() {
    return body;
  }
}

09-GREEN.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1", "answer2"))).toJson()
        .equals("[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}]"));
  }
}

class QuestionList {
  private Optional<Question> questionOpt;

  public QuestionList() {
    questionOpt = Optional.empty();
  }

  public QuestionList(Question question) {
    this.questionOpt = Optional.ofNullable(question);
  }

  public String toJson() {
    return questionOpt.map(question -> "[{\"body\": \"" + question.getBody() + "\", \"answers\": ["
        + question.getAnswers().stream().map(answer -> "\"" + answer + "\"").collect(Collectors.joining(", ")) + "]}]")
        .orElseGet(() -> "[]");
  }
}

class Question {
  private String body;
  private List<String> answers;

  public Question(String body, List<String> answers) {
    this.body = body;
    this.answers = answers;
  }

  public String getBody() {
    return body;
  }

  public List<String> getAnswers() {
    return answers;
  }
}

10-REFACTORING.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1", "answer2"))).toJson()
        .equals("[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}]"));
  }
}

class QuestionList {
  private Optional<Question> questionOpt;

  public QuestionList() {
    questionOpt = Optional.empty();
  }

  public QuestionList(Question question) {
    this.questionOpt = Optional.ofNullable(question);
  }

  public String toJson() {
    return questionOpt
        .map(question -> "[{\"body\": \"" + question.getBody() + "\", " + createAnswersField(question) + "}]")
        .orElseGet(() -> "[]");
  }

  private String createAnswersField(Question question) {
    return "\"answers\": ["
        + question.getAnswers().stream().map(answer -> "\"" + answer + "\"").collect(Collectors.joining(", ")) + "]";
  }
}

class Question {
  private String body;
  private List<String> answers;

  public Question(String body, List<String> answers) {
    this.body = body;
    this.answers = answers;
  }

  public String getBody() {
    return body;
  }

  public List<String> getAnswers() {
    return answers;
  }
}

11-REFACTORING.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1", "answer2"))).toJson()
        .equals("[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}]"));
  }
}

class QuestionList {
  private Optional<Question> questionOpt;

  public QuestionList() {
    questionOpt = Optional.empty();
  }

  public QuestionList(Question question) {
    this.questionOpt = Optional.ofNullable(question);
  }

  public String toJson() {
    return questionOpt.map(question -> "[" + question.toJson() + "]").orElseGet(() -> "[]");
  }
}

class Question {
  private String body;
  private List<String> answers;

  public Question(String body, List<String> answers) {
    this.body = body;
    this.answers = answers;
  }

  public String getBody() {
    return body;
  }

  public List<String> getAnswers() {
    return answers;
  }

  public String toJson() {
    return "{" + createBodyField() + ", " + createAnswersField() + "}";
  }

  private String createBodyField() {
    return "\"body\": \"" + body + "\"";
  }

  private String createAnswersField() {
    return "\"answers\": [" + answers.stream().map(answer -> "\"" + answer + "\"").collect(Collectors.joining(", "))
        + "]";
  }
}

12-GREEN.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

class Main {
  public static void main(String... args) {
    assert new QuestionList().toJson().equals("[]");
    assert (new QuestionList(new Question("body", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body2", Arrays.asList())).toJson()
        .equals("[{\"body\": \"body2\", \"answers\": []}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1", "answer2"))).toJson()
        .equals("[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}]"));
    assert (new QuestionList(new Question("body", Arrays.asList("answer1", "answer2")),
        new Question("body2", Arrays.asList("answer3", "answer4"))).toJson().equals(
            "[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}, {\"body\": \"body2\", \"answers\": [\"answer3\", \"answer4\"]}]"));
  }
}

class QuestionList {
  private List<Question> questions;

  public QuestionList() {
    questions = Arrays.asList();
  }

  public QuestionList(Question... questions) {
    this.questions = Arrays.asList(questions);
  }

  public String toJson() {
    return "[" + questions.stream().map(Question::toJson).collect(Collectors.joining(", ")) + "]";
  }
}

class Question {
  private String body;
  private List<String> answers;

  public Question(String body, List<String> answers) {
    this.body = body;
    this.answers = answers;
  }

  public String toJson() {
    return "{" + createBodyField() + ", " + createAnswersField() + "}";
  }

  private String createBodyField() {
    return "\"body\": \"" + body + "\"";
  }

  private String createAnswersField() {
    return "\"answers\": [" + answers.stream().map(answer -> "\"" + answer + "\"").collect(Collectors.joining(", "))
        + "]";
  }
}

13-REFACTORING.java

import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

class Main {
  public static void main(String... args) {
    QuestionRepository repo1 = new QuestionRepository() {
      @Override
      public QuestionList findAll() {
        return new QuestionList();
      };
    };

    QuestionRepository repo2 = new QuestionRepository() {
      @Override
      public QuestionList findAll() {
        return new QuestionList(new Question("body", Arrays.asList()));
      };
    };

    QuestionRepository repo3 = new QuestionRepository() {
      @Override
      public QuestionList findAll() {
        return new QuestionList(new Question("body2", Arrays.asList()));
      };
    };

    QuestionRepository repo4 = new QuestionRepository() {
      @Override
      public QuestionList findAll() {
        return new QuestionList(new Question("body", Arrays.asList("answer1", "answer2")));
      };
    };

    QuestionRepository repo5 = new QuestionRepository() {
      @Override
      public QuestionList findAll() {
        return new QuestionList(new Question("body", Arrays.asList("answer1", "answer2")),
            new Question("body2", Arrays.asList("answer3", "answer4")));
      };
    };

    assert repo1.findAll().toJson().equals("[]");
    assert repo2.findAll().toJson().equals("[{\"body\": \"body\", \"answers\": []}]");
    assert repo3.findAll().toJson().equals("[{\"body\": \"body2\", \"answers\": []}]");
    assert repo4.findAll().toJson().equals("[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}]");
    assert repo5.findAll().toJson().equals(
        "[{\"body\": \"body\", \"answers\": [\"answer1\", \"answer2\"]}, {\"body\": \"body2\", \"answers\": [\"answer3\", \"answer4\"]}]");

  }
}

interface QuestionRepository {
  QuestionList findAll();
}

class QuestionList {
  private List<Question> questions;

  public QuestionList() {
    questions = Arrays.asList();
  }

  public QuestionList(Question... questions) {
    this.questions = Arrays.asList(questions);
  }

  public String toJson() {
    return "[" + questions.stream().map(Question::toJson).collect(Collectors.joining(", ")) + "]";
  }
}

class Question {
  private String body;
  private List<String> answers;

  public Question(String body, List<String> answers) {
    this.body = body;
    this.answers = answers;
  }

  public String toJson() {
    return "{" + createBodyField() + ", " + createAnswersField() + "}";
  }

  private String createBodyField() {
    return "\"body\": \"" + body + "\"";
  }

  private String createAnswersField() {
    return "\"answers\": [" + answers.stream().map(answer -> "\"" + answer + "\"").collect(Collectors.joining(", "))
        + "]";
  }
}