编写Java程序，实现工厂模式的四则运算

可以回答这个问题。工厂模式是一种创建型设计模式，它提供了一种创建对象的最佳方式。在四则运算中，可以创建一个工厂类，根据不同的运算符创建不同的运算对象，从而实现四则运算。具体实现可以参考以下代码：

public interface Operation {
    double getResult(double num1, double num2);
}

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

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

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

public class DivOperation implements Operation {
    @Override
    public double getResult(double num1, double num2) {
        if (num2 == 0) {
            throw new IllegalArgumentException("除数不能为0");
        }
        return num1 / num2;
    }
}

public class OperationFactory {
    public static Operation createOperation(String operator) {
        Operation operation = null;
        switch (operator) {
            case "+":
                operation = new AddOperation();
                break;
            case "-":
                operation = new SubOperation();
                break;
            case "*":
                operation = new MulOperation();
                break;
            case "/":
                operation = new DivOperation();
                break;
        }
        return operation;
    }
}

public class Main {
    public static void main(String[] args) {
        double num1 = 10;
        double num2 = 5;
        String operator = "+";
        Operation operation = OperationFactory.createOperation(operator);
        double result = operation.getResult(num1, num2);
        System.out.println(num1 + " " + operator + " " + num2 + " = " + result);
    }
}