driver-core/src/main/com/mongodb/BasicDBObjectBuilder.java
public static BasicDBObjectBuilder start(final String key, final Object val) {
        return (new BasicDBObjectBuilder()).add(key, val);
    }
public static BasicDBObjectBuilder start(final String key, final Object val) {
        return (new BasicDBObjectBuilder()).add(key, val);
    }
Creates a builder initialized with the given key/value.

@param key The field name
@param val The value
@return the new builder