AbstractOperation.java

package u001;

/**
 * Created by HuGuodong on 2019/11/9.
 */
public abstract class AbstractOperation {

 private double a;
 private double b;

 public double getA() {
 return a;
 }

 public void setA(double a) {
 this.a = a;
 }

 public double getB() {
 return b;
 }

 public void setB(double b) {
 this.b = b;
 }

 public abstract double getResult();
}

class OperationAdd extends AbstractOperation {

 @Override
 public double getResult() {
 return getA() + getB();
 }
}

class OperationSub extends AbstractOperation {

 @Override
 public double getResult() {
 return getA() - getB();
 }
}

class OperationMult extends AbstractOperation {

 @Override
 public double getResult() {
 return getA() * getB();
 }
}

class OperationDiv extends AbstractOperation {

 @Override
 public double getResult() {
 if (getB() == 0) {
 throw new IllegalArgumentException("b can not be zero.");
 }
 return getA() / getB();
 }
}