简单工厂模式 | 易学教程

工厂：使用一个单独的类来做创造各种实例的过程（工厂类）

初学者代码毛病：

命名不规范
多个if判断导致每个if都要判断，多做无用功
除0判断，非法输入判断

代码应达到的要求：可维护（方便修改），可复用（能重复使用），可扩展（方便增加功能），灵活性好（方便调整功能，比如执行顺序）

设计模式使得程序更加灵活。

测试类：

1 public class testMain {
2     public static void main(String[] args) throws Exception {
3         Operation operation;
4         operation = OperationFactory.createOperate("/");
5         operation.numberA = 12;
6         operation.numberB = 3;
7         System.out.println(operation.getResult());
8     }
9 }

工厂类：

 1 public class OperationFactory {
 2     public static Operation createOperate(String operate){
 3         Operation op = null;
 4         switch (operate){
 5             case "+":
 6                 op = new OperationAdd();
 7                 break;
 8             case "-":
 9                 op = new OperationSub();
10                 break;
11             case "*":
12                 op = new OperationMul();
13                 break;
14             case "/":
15                 op = new OperationDiv();
16                 break;
17         }
18         return op;
19     }
20 }

运算类：

public class Operation {
    public double numberA = 0;
    public double numberB = 0;

    public double getResult() throws Exception {
        double result = 0;
        return result;
    }
}

加法类：

public class OperationAdd extends Operation{
    public double getResult(){
        double result = 0;
        result = numberA + numberB;
        return result;
    }
}

减法类：

1 public class OperationSub extends Operation{
2     public double getResult(){
3         double result = 0;
4         result = numberA - numberB;
5         return result;
6     }
7 }

乘法类：

public class OperationMul extends Operation {
    public double getResult(){
        double result = 0;
        result = numberA * numberB;
        return result;
    }
}

除法类：

public class OperationDiv extends Operation {
    public double getResult() throws Exception {
        double result = 0;
        if (numberB==0){
            throw new Exception("除数不能为0!");
        }
        result = numberA/numberB;
        return result;
    }
}

来源：https://www.cnblogs.com/z-dk/p/10513279.html

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简单工厂模式