设计模式之简单工厂模式

    今天看了简单工厂模式，总体来说这种模式是这样子的： 

   1、首先定义一个接口，这个接口里面定义了一些方法；

   2、有好几个类实现了这个接口；

   3、根据需求，通过一个工厂类来生成想要的一个类，这个类属于第2步里面说的类；

下面通过实现一个简单的加减乘除的功能来说明这个模式：

   1：

      定义一个接口：

     public interface Operation
     {
         public double calc();
     }

  2：

  分别定义加减乘除四个类，并且这四个类实现了Operation这个接口：

  public class AddOperation implements Operation
{
    public double A;
    public double B;
    
public AddOperation(double a, double b)
{
A = a;
B = b;
}


@Override
public double calc()
{
return A + B;
}
}

    public class SubOperation implements Operation
{
    public double A;
    public double B;
    
    public SubOperation(double a, double b)
{
A = a;
B = b;
}


@Override
public double calc()
{
return A - B;
}
}

public class MulOperation implements Operation
{
    public double A;
    public double B;
    
    public MulOperation(double a, double b)
{
A = a;
B = b;
}


@Override
public double calc()
{
return A * B;
}

}

public class DivOperation implements Operation
{
    public double A;
    public double B;
    
public DivOperation(double a, double b)
{
A = a;
B = b;
}


@Override
public double calc() 
{
double result = 0;
if (B == 0) {
try
{
throw new Exception("除数不能为零。");
} catch (Exception e)
{
e.printStackTrace();
}
}
else {
result = A / B;
}
return result;
}
    
}

 3：接着定义工厂类：

    public class OperationFactory
{
    public static Operation getOperation(String type, double A, double B) {
        Operation oper = null;
    switch (type) {
   
    case "+" :
    oper = new AddOperation(A, B);
    break;
    case "-" :
    oper = new SubOperation(A, B);
    break;
    case "*" :
    oper = new MulOperation(A, B);
    break;
    case "/" :
    oper = new DivOperation(A, B);
    break;
    default :
    System.out.println("不能识别该操作符！");
    }
    return oper;
    }
}

   这样子，就完成了一个简单的工厂模式了。

   下面是测试代码：

  public class Client
{
     public static void main(String[] args)
{
Operation oper_add = OperationFactory.getOperation("+", 2, 3);
System.out.println(oper_add.calc());

Operation oper_sub = OperationFactory.getOperation("-", 5, 3);
System.out.println(oper_sub.calc());

Operation oper_mul = OperationFactory.getOperation("*", 2,3);
System.out.println(oper_mul.calc());

Operation oper_div = OperationFactory.getOperation("/", 4,3);
System.out.println(oper_div.calc());
}
}