简单工厂模式

通过工厂来返回不同的对象，可使用同一种方法。

抽象类：

public abstract class Operation {
    private double numA;
    private double numB;
    private double result;
    
    public double getNumA() {
        return numA;
    }
    public void setNumA(double numA) {
        this.numA = numA;
    }
    public double getNumB() {
        return numB;
    }
    public void setNumB(double numB) {
        this.numB = numB;
    }
    public abstract double getResult();
    

}

加减乘数实现类：

public class AddOperation extends Operation {
    
    public double getResult() {
        
        return super.getNumA()+super.getNumB();
    }
    
}

public class SubOperation extends Operation  {
    public double getResult() {
        return super.getNumA()-super.getNumB();
    }
}

public class MulOperation extends Operation  {
    public double getResult() {
        return super.getNumA()*super.getNumB();
    }
}

public class DivOperation extends Operation {
    @Override
    public double getResult() {
        return super.getNumA()/super.getNumB();
    }
}

工厂类与实现：

public class OperationFactory {
    public  static  Operation createOperation(String type){
        switch (type) {
        case "+":
            return new AddOperation();
        case "-":
            return new SubOperation();
        case "*":
            return new MulOperation();
        case "/":
            return new DivOperation();
        default:
            break;
        }
        return null;
        
    }
    
    public static void main(String[] args) {
        Operation operation;
        operation=OperationFactory.createOperation("+");
        operation.setNumA(1);
        operation.setNumB(1);
        System.out.println(operation.getResult());
    }
}

这样通过控制显示层的代码即可控制整个实现逻辑。。。