@Test
    public void howToAddNumerically() {
        Table table = dynamo.getTable(TABLE_NAME);
        GetItemOutcome outcome = table.getItemOutcome(new GetItemSpec()
            .withPrimaryKey(HASH_KEY, FIRST_CUSTOMER_ID, RANGE_KEY, ADDRESS_TYPE_WORK)
            .withConsistentRead(true)
        );
        Item item = outcome.getItem();
        final int oldZipCode = item.getInt("zipcode");

        // Increments the zip code attribute
        table.updateItem(HASH_KEY, FIRST_CUSTOMER_ID, RANGE_KEY, ADDRESS_TYPE_WORK,
                new AttributeUpdate("zipcode").addNumeric(1));
        outcome = table.getItemOutcome(new GetItemSpec()
            .withPrimaryKey(HASH_KEY, FIRST_CUSTOMER_ID, RANGE_KEY, ADDRESS_TYPE_WORK)
            .withConsistentRead(true));
        item = outcome.getItem();
        int newZipCode = item.getInt("zipcode");
        assertEquals(oldZipCode + 1, newZipCode);

        // Decrements the zip code attribute
        table.updateItem(HASH_KEY, FIRST_CUSTOMER_ID, RANGE_KEY, ADDRESS_TYPE_WORK,
                new AttributeUpdate("zipcode").addNumeric(-1));
        outcome = table.getItemOutcome(new GetItemSpec()
            .withPrimaryKey(HASH_KEY, FIRST_CUSTOMER_ID, RANGE_KEY, ADDRESS_TYPE_WORK)
            .withConsistentRead(true));
        item = outcome.getItem();
        newZipCode = item.getInt("zipcode");
        assertEquals(oldZipCode, newZipCode);
    }
Sample code to update items to a dynamo table.
src/samples/AmazonDynamoDBDocumentAPI/quick-start/com/amazonaws/services/dynamodbv2/document/quickstart/F_UpdateItemTest.java