Class Cast Hell

ClassCastException.cs

var doc = new BsonDocument("x", 10.0);

var x1 = doc["x"].AsInt32;              // breaks
var x2 = (int)doc["x"];                 // breaks
var x3 = doc["x"].ToInt32();            // ok

ClassCastException.java

        collection.createIndex(new BasicDBObject("x", 1));                                     // covering index

        collection.insert(new BasicDBObject("x", 1));
        collection.insert(new BasicDBObject("x", 2));
        collection.insert(new BasicDBObject("x", 3));

        DBObject doc = collection.findOne(new BasicDBObject("x", new BasicDBObject("$lt", 3)), // query
                                          new BasicDBObject("x", 1).append("_id", 0));         // projection

        int x = ((Number) doc.get(("x"))).intValue();    // a safe but probably rarely used workaround

        x = (Integer) doc.get(("x"));                    // but this will blow up with a ClassCastException
 
 

Java Output

java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.Integer