1_before_if_java8.java

// 간단한 덧셈 뺄섬을 하는 Service class
// single responsibility principle도 위반
// 전혀 oop적인 코드도 아니다.
class CalculationService {
  public int calculate(char calculation, int num1, int num2) {
    if (calculation == '+') {
      return num1 + num2;
    } else if (calculation == '-') {
      return num1 - num2;
    }
  }
}

2_before_java8_strategy_pattern.java

// strategy pattern으로 리팩토링
interface Calculation {
  int calculate(int num1, int num2);
}

class Addition implements Calculation {
  @Override
  public int calculate(int num1, int num2) {
    return num1 + num2;
  }
}

class Subtraction implements Calculation {
  @Override
  public int calculate(int num1, int num2) {
    return num1 - num2;
  }
}

class CalculateService {
  private final Calculation calculation;
  
  public CalculateService(Calculation calculation) {
    this.calculation = calculation;
  }
  
  public int calculate(int num1, int num2) {
    return calculation.calculate(num1, num2);
  }
}

// 실행
final int addition = new CalculateService(new Addition()).calculate(1, 2)
final int subtraction = new CalculateService(new Subtraction()).calculate(1, 2)

3_above_java8.java

// 자바 8 이후에는 람다식을 통해서 high-order functions가 간편하게 가능하다.
// 그래서 아래와같이 간단하게 구현이 가능하다.
interface Calculation {
  int calculate(int num1, int num2);
}

class CalculateService {
  public int calculate(Calculation calculation, int num1, int num2) {
    return calculation.calculate(num1, num2);
  }
}

// 실행
final int addition = new CalculateService().calculate((num1, num2) -> num1 + num2, 1, 2)
final int subtraction = new CalculateService().calculate((num1, num2) -> num1 - num2, 1, 2)