在编写一个计算器程序时，可以将业务逻辑和显示分离，业务逻辑封装为一个类（封装）；如果要新添加一种运算，可以先创建一个Operation的基类，然后各种运算从Operation类继承，并实现GetResult()虚函数，这时添加新的运算只需要派生一个新的类，即不需要之前的运算参与编译。如何让计算器知道我是希望使用哪种运算呢？应该考虑单独的类来做这个创造实例的过程，这就是工厂。创建一个OperationFactory类，传入参数，函数createOperate就可以实例化出合适的对象。
Java代码如下：
public class OperationFactory {
public static abstract class Operation
{
private double _numberA = 0;
private double _numberB = 0;
public double get_numberA() {
return _numberA;
}
public void set_numberA(double _numberA) {
this._numberA = _numberA;
}
public double get_numberB() {
return _numberB;
}
public void set_numberB(double _numberB) {
this._numberB = _numberB;
}
abstract double GetResult();
// TODO Auto-generated constructor stub
}
public static class OperationAdd extends Operation
{
double GetResult()
{
double result = get_numberA() + get_numberB();
return result;
}
}
public static class OperationSub extends Operation
{
double GetResult() {
double result = get_numberA() - get_numberB();
return result;
}
}
public static Operation createOperate(String operate){
Operation oper = null;
if (operate.equals("+")) {
oper = new OperationAdd();
}
else if (operate.equals("-")) {
oper = new OperationSub();
}
return oper;
}
public static void main(String[] args) {
Operation oper;
oper = OperationFactory.createOperate("+");
oper.set_numberA(1);
oper.set_numberB(2);
double result = oper.GetResult();
}
}
