Java – lists and lists

Why lose type security when using list and use list < Object >? Aren't they basically the same?

Editor: I found the following compilation errors

public class TestClass
{
    static void func(List<Object> o,Object s){
        o.add(s);
    }

    public static void main(String[] args){
        func(new ArrayList<String>(),new Integer(1));
    }
}

And this is not

public class TestClass
{
    static void func(List o,new Integer(1));
    }
}

Why?

Solution

No, they're not the same thing

If you provide an API,

class API {
  static List<Object> getList() { ... }
  static void modifyList(List<Object> l) { ... }
}

Improper use of client

List<Integer> list = API.getList();
API.modifyList(list);
for (Integer i : list) { ... }  // Invalid

So when your API specifies list < Object > they get a compile time error, but when the API GetList () returns a list and the API When modifylist (list) accepts a list without generic type parameters, they will not

Edit:

In the comments you mentioned change

void func(List<Object> s,Object c) { s.add(c); }

to

void func(List s,Object c) { s.add(c); }

so that

func(new List<String>(),"");

I can work

That's illegal security The type safe way to do this is

<T> void func(List<? super T> s,T c) { s.add(c); }

This basically means that func is a parameterized function, which accepts a list, whose type can be any superclass of T, and the value of type T, and adds the value to the list