public BasicDBObjectBuilder push(final String key) {
        BasicDBObject o = new BasicDBObject();
        _cur().put(key, o);
        _stack.addLast(o);
        return this;
    }
public BasicDBObjectBuilder push(final String key) {
        BasicDBObject o = new BasicDBObject();
        _cur().put(key, o);
        _stack.addLast(o);
        return this;
    }
public BasicDBObjectBuilder push ( final String key ) { BasicDBObject o = new BasicDBObject ( ) ; _cur ( ) . put ( key , o ) ; _stack . addLast ( o ) ; return this ; }
Creates an new empty object and inserts it into the current object with the given key. The new child object becomes the active one.

@param key the field name
@return {@code this} so calls can be chained
Creates an new empty object and inserts it into the current object with the given key . The new child object becomes the active one .