Why does indexOf method of ArrayList work?

Please consider the following code (Its quite simple)

public class Main {

    public static class A{
        int id;

        public A(final int id){
            this.id = id;
        }

        @Override
        public boolean equals(final Object obj) {
            if(obj instanceof A){
                final A a = (A) obj;
                return id == a.id;
            }
            return false;
        }
    }

    public static void main(final String[] args) {
        final List<A> items = new ArrayList<A>();
        items.add(new A(0));
        items.add(new A(1));

        final Object obj = new A(1);
        System.out.println(items.indexOf(obj));
    }
}

When I run this code, 1 will be logged in the console. In my opinion it shouldn't be 1 rather it should be -1. I've looked into the indexOf source code. Exactly copy/paste from there:

public int indexOf(Object o) {
    if (o == null) {
        for (int i = 0; i < size; i++)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = 0; i < size; i++)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}

As we know when my code wants to be run the else segment of the above code starts to execute. And as you can see in there, statement o.equals(elementData[i]) will be executed. So far everything is okay and I have no problems

My Problem

Type of variable o in the above method is Object and when we call equals method of it, In my opinion equals method of a generic Object will be executed, In the other side I've look at equals method of Object source code. I copy/paste it here:

public boolean equals(Object obj) {
    return (this == obj);
}

Now, in the for-loop at indexOf method, It shouldn't any item be matched with o object because there is no item in the array which is equal to o object, in == point of view

Now I wonder how is output of my code equals to 1. Can any one please help me?

Thanks