1.创建运算的接口

public interface Operation {    //提供计算两个数字的方法    double getResult(double num1,double num2);}

2.创建对应的加减乘除四个实现类

public class Addition implements Operation { //加法    @Override    public double getResult(double num1, double num2) {        return num1+num2;    }}

public class Minus implements Operation { //减法    @Override    public double getResult(double num1, double num2) {        return num1-num2;    }}

public class Multiplication implements Operation {//乘法    @Override    public double getResult(double num1, double num2) {        return num1*num2;    }}

public class Division implements Operation {//除法    @Override    public double getResult(double num1, double num2) {        return num1/num2;    }}

3.创建工厂类

public class OperationFactory {  //计算机的工厂类    /*     * 工厂模式 是我们最常用的实例化对象的模式！     * 用工厂的方法替代new！     * 虽然代码量没有减少  但是 提高了程序的扩展性！     */    public static  Operation  getOperation(String o){        Operation operation=null; //多态        switch (o) {        case "+":            operation=new Addition();            break;        case "-":            operation=new Minus();            break;        case "*":            operation=new Multiplication();            break;        case "/":            operation=new Division();            break;        }        return  operation;    }}

 

4.创建测试类 运行 测试结果

public class FactoryTest {    public static void main(String[] args) {        Scanner scanner=new Scanner(System.in);        System.out.println("请输入第一个数字：");        double num1 = scanner.nextInt();        System.out.println("请输入运算符：");        String operation = scanner.next();        System.out.println("请输入第二个数字：");        double num2 = scanner.nextInt();        //创建运算的实例对象        Operation o = OperationFactory.getOperation(operation);        //输出结果        System.out.println(o.getResult(num1, num2));    }}