设计模式——工厂模式

没有什么一战成名，都只是百炼成钢！

本文配合《大话设计模式》工厂模式一起使用，因为原书中使用的C#代码，看起来有点麻烦！所以我变动了一下改成了Java代码，若是有错误还望指出，本人将感激不尽！谢谢！

1. 代码要做到可维护、可复用、可扩展、灵活性好

Operation.java

package factory;

public class Operation {
	private double numberA;
	private double numberB;

	public double getNumberA() {
		return numberA;
	}

	public double getNumberB() {
		return numberB;
	}

	public void setNumberA(double numberA) {
		this.numberA = numberA;
	}

	public void setNumberB(double numberB) {
		this.numberB = numberB;
	}
	public double getResult() {
		double result = 0;
		return result;
	}
}

OperationAdd继承于Operation

package factory;

public class OperationAdd extends Operation {
	@Override
	public double getResult() {
		// TODO Auto-generated method stub
		double result = getNumberA()+getNumberB();
		return result;
	}
}

package factory;

public class OperationSub extends Operation{
	@Override
	public double getResult() {
		// TODO Auto-generated method stub
		double result = getNumberA()-getNumberB();
		return result;
	}
}

package factory;

public class OperationMul extends Operation{
	@Override
	public double getResult() {
		// TODO Auto-generated method stub
		double result = getNumberA()*getNumberB();
		return result;
	}
}

package factory;

public class OperationDiv extends Operation {
	@Override
	public double getResult() {
		// TODO Auto-generated method stub
		double result = 0;
		try {
			result = getNumberA() / getNumberB();
		} catch (Exception e) {
			// TODO: handle exception
			System.err.println("除数不能为0！运算出错！");
		}
		return result;
	}
}

package factory;

public class OperationFactory {
	
	public static Operation createOperation(String operate) {
		Operation oper = null;
		switch (operate) {
		case "+":
			oper = new OperationAdd();
			break;
		case "-":
			oper = new OperationSub();
			break;
		case "*":
			oper = new OperationMul();
			break;
		case "/":
			oper = new OperationDiv();
			break;
		default:
			System.err.println("运算符号有错误！异常退出！");
			break;
		}
		return oper;
	}
}

package factory;

public class client {

	public static void main(String[] args) {
		Operation oper;
		oper = OperationFactory.createOperation("---");
		try {
			oper.setNumberA(1);
			oper.setNumberB(2);
			double result = oper.getResult();
			System.out.println(result);
		} catch (NullPointerException e) {
			// TODO: handle exception
			System.err.println("空指针异常！！！！！！");
		}
	}
}