简单工厂模式（Java实现）

• Factory：工厂类，简单工厂模式的核心，它负责实现创建所有实例的内部逻辑。工厂类的创建产品类的方法可以被外界直接调用，创建所需的产品对象。
• IProduct：抽象产品类，简单工厂模式所创建的所有对象的父类，它负责描述所有实例所共有的公共接口。
• Product：具体产品类，是简单工厂模式的创建目标。

工厂类：创建运算

抽象产品类：两个数之间的运算以及得到的结果

具体产品类：加减乘除四则运算

Java源码：

public class OperationFactory {
	public static Operation createOperate(String operate) {
        Operation operation = null;
        switch (operate) {
            case "+":
                operation = new OperationAdd();
                break;
            case "-":
                operation = new OperationSub();
                break;
            case "*":
                operation = new OperationMul();
                break;
            case "/":
                operation = new OperationDiv();
                break;
        }
        return operation;
    }
}

public abstract class Operation {
		private double numberA;
	    private double numberB;
	 
	    public double getNumberA() {
	        return numberA;
	    }
	 
	    public void setNumberA(double numberA) {
	        this.numberA = numberA;
	    }
	 
	    public double getNumberB() {
	        return numberB;
	    }
	 
	    public void setNumberB(double numberB) {
	        this.numberB = numberB;
	    }
	 
	    public abstract double GetResult() throws Exception;
}

public class OperationAdd extends Operation {
	
	@Override
    public double GetResult() {
        return getNumberA() + getNumberB();
    }

}

public class OperationSub extends Operation {

	@Override
	public double GetResult() throws Exception {
		return getNumberA() - getNumberB();
	}

}

public class OperationMul extends Operation {

	@Override
	public double GetResult() throws Exception {
		return getNumberA() * getNumberB();
	}

}

public class OperationDiv extends Operation {

	@Override
	public double GetResult() throws Exception {
		if (getNumberB() == 0)
            throw new Exception("除数不可以为 0 !");
		return getNumberA() / getNumberB();
	}

}

public class Main {
	
	public static void main(String[] args) throws Exception {
		Operation operation = OperationFactory.createOperate("+");
        operation.setNumberA(1);
        operation.setNumberB(2);
        double result = operation.GetResult();
        System.out.println(result);
    }
}