工厂类
public class Factory{

 public static Common getCommon(char c){
		Common common=null;
		switch (c) {
		case 'A':
			common=new A();
			break;
		case 'B':
			common=new B();
			break;
		}
		return common;
         }

}
公共类
public class Common {

 public String getXX(){
	return "";	 
 }

}

子类A
public class A extends Common{

 public String getXX(){
		return "得到A";	 
	 }

}

子类B
public class B extends Common{

 public String getXX(){
		return "得到B";	 
	 }

}

调用：给工厂类传递参数得到对象
public static void main(String[] args) {

	Common common =null;
	common=Factory.getCommon('A');
	System.out.println(common.getXX());

}