Pass a generic Object to a list in a method - JAVA

Question

I've two question, They may be silly questions but it got me confused now.

QUESTION 1:

I've this code:

private List<Car> carList;

public void setData(List<Object> list)
{
    this.carListist = list;
}

But on this.carList = list I get a compiling error: incompatible types, required: List<Car> but found List<Object>

My question is, why this error? Isn't List a list of objects type Car? So why doesn't it accept an Object there?

QUESTION 2: I change the above code to the following and the error goes away:

private List<Object> carList;

public void setData(List<Object> list)
{
    this.carListist = list;
}


public Object getValueAt(int row, int column) {

    Car car = carList.get(row); //Compiling error here

    switch(column)
    {
        (...)
    }
    (..)

Ther compiling error (signed in the code comment) is incompatible types, required Car but found Object What I don't understand is, now list is defined as an object list. Car is an object. Why car, as being an object, is not accepted?

Anyway to fix this for both question 1 and 2?

To OP: In both 1 and 2 apply SLaks' comment. Note that there is no covariance, i.e `A extends B` does not imply `List extends List`. — nanofarad, Sep 29 '13 at 21:37
`Car` is **always** an `Object`. `Object` could **potentially** be a `Car`. — PM 77-1, Sep 29 '13 at 21:40

score 1 · Accepted Answer · answered Sep 29 '13 at 21:38

1

It is not because every Car is an Object that a list of cars is also a list of objects, in your example what if the list of objects contains a boat and not a car....

answered Sep 29 '13 at 21:38

GerritCap

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9

Or a socket, for that matter... – nanofarad Sep 29 '13 at 21:39

Pass a generic Object to a list in a method - JAVA

1 Answers1