简单工厂模式

面向对象三大特性：封装、继承和多态。
用简单工厂模式实现松耦合的设计。
简单工厂模式，也就是说，到底要实例化谁，将来会不会增加实例化的对象，对于很容易变化的地方，应该考虑用一个单独的类来做这个创造的过程，这就是工厂。

package com.jshx.operation;
/**
 * 操作父类
 * @author duanpf
 *
 */
public class Operation {
	private double numberA=0;
	private double numberB=0;
	
	public double getResult() throws Exception{
		double result = 0;
		return result;
	}
	
	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;
	}
}

package com.jshx.operation;

public class OperationAdd extends Operation {

	@Override
	public double getResult() throws Exception{
		double result = 0;
		result = getNumberA() + getNumberB();
		return result;
	}
}

package com.jshx.operation;

public class OperationSub extends Operation {

	@Override
	public double getResult() throws Exception{
		double result = 0;
		result = getNumberA() - getNumberB();
		return result;
	}
}

package com.jshx.operation;

public class OperationMul extends Operation {

	@Override
	public double getResult() throws Exception{
		double result = 0;
		result = getNumberA() * getNumberB();
		return result;
	}
}

package com.jshx.operation;

public class OperationDiv extends Operation {

	@Override
	public double getResult() throws Exception {
		double result = 0;
		if(getNumberB() == 0 ){
			throw new Exception("除数不能为0。");
		}
		result = getNumberA() / getNumberB();
		return result;
	}
}

package com.jshx.operation;
/**
 * 运算类工厂
 * @author duanpf
 *
 */
public class OperationFactory {
	public static Operation createOperation(String operate){
		Operation oper=null;
		char[] ch=operate.toCharArray();
		switch(ch[0]) {
		case '+':
			oper = new OperationAdd();
			break;
		case '-':
			oper = new OperationSub();
			break;
		case '*':
			oper = new OperationMul();
			break;
		case '/':
			oper = new OperationDiv();
			break;
		}
		return oper;
	}
}

package com.jshx.operation;

public class OperationTest {
	public static void main(String[] args) throws Exception {
		Operation oper = new Operation();
		oper = OperationFactory.createOperation("-");
		oper.setNumberA(1);
		oper.setNumberB(2);
		double result = oper.getResult();
		System.out.println(result);
	}
}