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。。。