how to delete the auto generated item from push method from Firebase Real-time database

Question

I am new to Firebase and I am facing a problem in delete an item from the recycler view I created. but I am unable to understand how to delete items using an auto-generated key. This is how I added item into the database :

 DatabaseReference reference = FirebaseDatabase.getInstance().getReference("categories");
     String key = reference.push().getKey();
    reference.child(key).setValue(categoryData).addOnCompleteListener(new OnCompleteListener<Void>() {
        @Override
        public void onComplete(@NonNull Task<Void> task) {
            if(task.isSuccessful()){

                Toast.makeText(add_category.this, "Category added", Toast.LENGTH_SHORT).show();
                finish();

            }
        }
    }).addOnFailureListener(new OnFailureListener() {
        @Override
        public void onFailure(@NonNull Exception e) {
            Toast.makeText(add_category.this, "Failed to add", Toast.LENGTH_SHORT).show();
        }
    });

Answer 1

As in your comment, if you want to delete, for example, the second item, please use the following lines of code:

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference secondChildRef = rootRef.child("categories").child("-M1qUEGi0u4rX5Ju59r4");
secondChildRef.removeValue().addOnCompleteListener(new OnCompleteListener<Void>() {
    @Override
    public void onComplete(@NonNull Task<Void> task) {
        if (task.isSuccessful()) {
            Log.d("TAG", "Second item deleted!");
        }
    }
});

So to delete a particular item, you to know its ID so you can add it to the reference.