策略模式

• Strategy, 封装多个算法类, 更换策略，调用方式一致

• public interface ICalculator {
      public int calculate(String exp);
  }
  public class Minus extends AbstractCaculator implements ICalculator {
      @Override
      public int calculate(String exp) {
          int arrayInt[] = split(exp, "-");
          return arrayInt[0] - arrayInt[1];
      }
  }
  public class AbstractCalculator {
      public int[] split(String exp, String opt) {
          String[] array = exp.split(opt);
          int arrayInt[] = new int[2];
          arrayInt[0] = Integer.parseInt(array[0]);
          arrayInt[1] = Integer.parseInt(array[1]);
          return arrayInt;
      }
  }
  Icalculator cal = new Minus();
  cal.calculate(exp);