将java.lang.object转换为Integer时出现问题

Question

Hi am developping a java web project with spring mvc and hibernate. I have a list of cars in carList. Now I want to retrieve the car type of each car. So I initialise another list carType. and then loop into carList and append the car type in the list of carType. When i output the value store in carType, it gives [Ljava.lang.Object;@255a8ce4. Can someone help me? The type of list should be object. Because I am sending this list to birt reporting to display in pdf.

List<Object> carList=getCarService().retrieveAllCarsAssignedToManagers(CarNo, DeptNo);

    List<Object> carType = new ArrayList<Object> ();
    for (Object carLists:carList) {
         carType.add(getcarService().retrieveAllCarType(Integer.valueOf(carLists.toString())));

    }
    for (int i = 0;i < carType.size(); i++) {
        System.out.println("Cars:  " + carType.get(i));
    }

Answer 1

You get Ljava.lang.Object;@255a8ce4. because your method retrieveAllCarType returns an array or list and not what you are expecting. When you put your list into System.out.print then it calls toString method of that list internally. The class of the list doesn't implement toString method so you get the default toString output.

Try System.out.println(java.util.Arrays.toString(carType.get(i).toArray()));

Answer 2

1) You define the List<Object> carType , the object here means the list can contain everything, including collections(such as List , Map and so on).

According to your code, you should put the integer cartype to the list, but you put a List<Object> to List<Object> , then elements in List carType is a List<Object> . so when you call

carType.get(i)

it returns a List!

If you can confirm that the carType is a number, you can define the carType as List<Integer> , then you can never put a List to carType, only Intergers are allowed in carType.

2）sysout one object will call his default toString() , your output is the default toString() of List type. It output the classname and it's hashcode.

Answer 3

You are providing too few information to get exact issue in your code. But I analyzed it by undergoing you code and question. There is one mistake done at

Integer.valueOf(carLists.toString()).

A list holds any type of information, like any type of object (String, List, Map, Set) and you are trying to convert that list into an Integer. You should try removing Integer.valueOf() and check what the list contains.

Answer 4

thanks for you help. I really apreaciate. Manage to solve the issue using addAll instead of add.