核心理念

• 根据不同的参数返回不同的实例
• 专门用一个类来创建其它类的实例
• 创建的类都具用共同的父类

优缺点

优点

• 对象的创建和业务的处理分离开来，可以降低系统的耦合性
• 新增业务只需新增处理类即可，不影响原来的业务处理类

缺点

• 工厂类需要根据参数判断返回的类，与开闭原则有点相违背

代码示例

操作类

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();
}

简单工厂类

public class OperationFactory {
    public Operation createOperate(String operate){
        if("+".equals(operate)){
            return new AddOperation();
        } else if("-".equals(operate)){
            return new SubOperation();
        }else{
            return null;
        }
    }
}

加法运算类

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

减法运算类

public  class SubOperation extends Operation {
    @Override
    public double getResult() {
        return getNumberA() - getNumberB();
    }
}

测试

public class AppRun {
    public static void main(String[] args) {
        OperationFactory operationFactory = new OperationFactory();
        Operation operate = operationFactory.createOperate("+");
        operate.setNumberA(1.2);
        operate.setNumberB(33.3);
        System.out.println(operate.getResult());
    }
}