大话设计模式之简单工厂模式

背景需求：

模拟一个简单计算器。

UML类图：

说明：

抽象类AbstractOperation有一个抽象方法getResult和两个成员变量，加减乘除分别继承AbstractOperation并实现getResult方法即可。OperationFactory是一个简单工厂方法，可根据入参实例化不同的子类。

demo:

AbstractOperation类：

public abstract class AbstractOperation {

    private Double firstNumber;
    private Double secondNumber;

    public abstract Double getResult() throws Exception;

    public Double getFirstNumber() {
        return firstNumber;
    }

    public void setFirstNumber(Double firstNumber) {
        this.firstNumber = firstNumber;
    }

    public Double getSecondNumber() {
        return secondNumber;
    }

    public void setSecondNumber(Double secondNumber) {
        this.secondNumber = secondNumber;
    }
}

加法类OperationAdd:

public class OperationAdd extends AbstractOperation {
    @Override
    public Double getResult() {
        return getFirstNumber() + getSecondNumber();
    }
}

减法类OperationSub:

public class OperationSub extends AbstractOperation {
    @Override
    public Double getResult() {
        return getFirstNumber() - getSecondNumber();
    }
}

简单工厂类OperationFactory:

public class OperationFactory {

    public static AbstractOperation createOperation(String operate){
        AbstractOperation operation = null;

        switch (operate){
            case "+":operation = new OperationAdd();break;
            case "-":operation = new OperationSub();break;
            default:break;
        }
        return operation;
    }
}

客户端测试类：

public class Main {

    public static void main(String[] args) throws Exception {

        AbstractOperation operation = 
   OperationFactory.createOperation("+");
        operation.setFirstNumber(10d);
        operation.setSecondNumber(20d);
        System.out.println(operation.getResult());

    }
}

总结：

简单工厂模式适用于需要创建大量相同类型(父类相同或实现相同接口)实例的情景