有誰能解釋下多態(tài)的用處在哪呢？自己不太明白

//Traffic類
package?com.edu;

public?class?Traffic?{
	public?String?TrafficName;	//交通工具的名稱
	public?int?maxNum;		//交通工具的最大承載量
	
	public?void?showData(){
		System.out.println(TrafficName+"這種交通工具最多允許乘坐："+maxNum+"人");
	}
}

//Car類
package?com.edu;

public?class?Car?extends?Traffic{
	public?Car(int?max){
		TrafficName?=?"汽車";
		maxNum?=?max;
	}
}

//Boat類
package?com.edu;

public?class?Boat?extends?Traffic{
	public?Boat(int?max){
		TrafficName?=?"小船";
		maxNum?=?max;
	}
}

//Intial類
package?com.edu;
import?java.util.Scanner;

public?class?Initial?{

	/**
	?*?@param?args
	?*/
	public?static?void?main(String[]?args)?{
		//?TODO?Auto-generated?method?stub
		Traffic?tool?=?new?Traffic();
		System.out.print("請輸入交通工具的名稱：");
		Scanner?input?=?new?Scanner(System.in);
		String?TrafficName?=?input.next();
		System.out.print("請輸入交通工具的最大乘載量：");
		int?maxNum?=?input.nextInt();
		if(TrafficName.equals("汽車")){
			tool?=?new?Car(maxNum);
		}else?if(TrafficName.equals("小船")){
			tool?=?new?Boat(maxNum);
		}
		
		tool.showData();
	}
}