一.简介

实例化对象的时候不再使用 new Object()形式，可以根据用户的选择条件来实例化相关的类。对于客户端来说，去除了具体的类的依赖,降低了程序的耦合度。只需要给出具体实例的描述给工厂，工厂就会自动返回具体的实例对象。

二.实例介绍

1.设计一个简易计算器

功能描述:使用简单工厂设计模式来实现一个能进行加、减、乘、除运算的简单计算器

2.UML类图

image.png

3.代码如下：

运算接口

public interface Operation {
    Double getResult(Double numberA, Double numberB);
}

加法类实现运算接口

public class OperationAdd implements Operation {
    public Double getResult(Double numberA, Double numberB) {
        return numberA + numberB;
    }
}

减法类实现运算接口

public class OperationSub implements Operation {
    public Double getResult(Double numberA, Double numberB) {
        return numberA - numberB;
    }
}

乘法类实现运算接口

public class OperationMul implements Operation {
    public Double getResult(Double numberA, Double numberB) {
        BigDecimal a1 = new BigDecimal(Double.toString(numberA));
        BigDecimal b1 = new BigDecimal(Double.toString(numberB));
        BigDecimal result = a1.multiply(b1);// 相乘结果
        return result.doubleValue();
    }
}

除法类实现运算接口

public class OperationDiv implements Operation {
    private final int scale = 2;                //保留小数位数
    public Double getResult(Double numberA, Double numberB) {
        try {
            if (numberB == 0.0) throw new Exception("除数不能为0");
            BigDecimal b1 = new BigDecimal(Double.toString(numberA));
            BigDecimal b2 = new BigDecimal(Double.toString(numberB));
            return b1.divide(b2,scale,BigDecimal.ROUND_HALF_UP).doubleValue();
        } catch (Exception e) {
            System.out.println("异常原因:"+e);
        }
        return null;
    }
}

简单运算工厂类

public class OperationFactory {
    public static Operation createOperate(String operate){
        Operation operation = null;
        if (operate.equals("+")){
            operation = new OperationAdd();
        }else if(operate.equals("-")){
            operation = new OperationSub();
        }else if(operate.equals("*")){
            operation = new OperationMul();
        }else if(operate.equals("/")){
            operation = new OperationDiv();
        }
        return operation;
    }
}

客户端测试代码如下：

public class Test {
    public static void main(String[] args){
        Operation operationAdd = OperationFactory.createOperate("+");
        System.out.println("1.0+2.0="+operationAdd.getResult(1.0, 2.0));
        System.out.println();

        Operation operationSub = OperationFactory.createOperate("-");
        System.out.println("2.5-1.0="+operationSub.getResult(2.5, 1.0));
        System.out.println();

        Operation operationMul = OperationFactory.createOperate("*");
        System.out.println("12.5*2.3="+operationMul.getResult(12.5, 2.3));
        System.out.println();

        Operation operationDiv = OperationFactory.createOperate("/");
        System.out.println("15.0/2.5="+operationDiv.getResult(15.37, 2.5));
        System.out.println();

        Operation operationDivException = OperationFactory.createOperate("/");
        System.out.println("12.5/0.0="+operationDivException.getResult(12.5, 0.0));
    }
}

测试结果:

image.png