对象：
public class car{
private String name；
private String category；
private String num；
}
List<Car> carList = new ArrayList<>();
Car car = new Car();
car.setName("宝马");
car.setCategory("越野");
car.setNum("3");
carlList.add(car);
Car car1 = new Car();
car.setName("宝马");
car.setCategory("轿车");
car.setNum("2");
carlList.add(car1);
Car car2 = new Car();
car.setName("奥迪");
car.setCategory("越野");
car.setNum("5");
carlList.add(car2);
Car car3 = new Car();
car.setName("奥迪");
car.setCategory("跑车");
car.setNum("1");
carlList.add(car3);
如上面所示数据，现在想实现最终结果是 一个新的List对象，[
```
{
"品牌" : "奥迪",
"越野":"5",
"轿车":"0",
"跑车":"1"
},
{
"品牌" : "宝马",
"越野":"3",
"轿车":"2",
"跑车":"0"
}
```]
想请教一下， 使用stream方法的话怎么处理，
