java.lang.Long cannot be cast to java.math.BigInteger

Question

My program has a method that fetches the count of a particular row and convert it into BigInteger:

private BigInteger getSameSatPremise(ServiceAgreement sa) {
BigInteger count = BigInteger.ZERO;

    StringBuffer queryHql = new StringBuffer();
    queryHql.append("from Table t1");
    Query query = createQuery(queryHql.toString());
    query.addResult("count", "count(distinct t1.column1)");
    if (query.listSize() > 0) {
        count = (BigInteger) query.firstRow();
    }
    return count;
}

The casting works fine when the result from the query is 0. But I get a casting error like below when the result from the query is 2.

Caused by: java.lang.ClassCastException: java.lang.Long cannot be cast to java.math.BigInteger

Can anyone help.

Why do you think you can cast that? Use `BigInteger.valueOf(query.firstRow())`. — Tom, Apr 06 '16 at 11:33
Methinks this question is reasonable, especially if the OP comes from C++. — Bathsheba, Apr 06 '16 at 11:39
Why are you trying to widen a `long`? If the column is a long type, why not use `long`? — Elliott Frisch, Apr 06 '16 at 11:44
`casting works fine when the result from the query is 0` No. In that case `query.listSize() > 0` you don't cast. You return the initial value of `count` which is `BigInteger.ZERO`. — SubOptimal, Apr 06 '16 at 11:52
@Tom query.firstRow() is a Object type. Maybe you'll have to do some research next time before answering. — Vishnu Priyan Rangasamy, Apr 06 '16 at 12:53
Since your were inable to define which classes/libraries you're using, it was impossible to do research on that. That `query.firstRow()` returns `Object` instead of `Long` (or `long`) is crucial information and it _needs_ to be in that question. And please, learn the difference between "answering" and commenting. — Tom, Apr 06 '16 at 13:01

Bathsheba · Answer 1 · 2016-04-06T12:38:43.230

12

Java ain't C++, you can't write your own conversion operators.

In Java you need to use explicit functions to do what you want. In your case that's the considerably more verbose

BigInteger.valueOf(query.firstRow())

edited Apr 06 '16 at 12:38

answered Apr 06 '16 at 11:39

Bathsheba

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query.firstRow() is not a Long but an Object. BigInteger.valueOf(query.firstRow()) will not work in this case. – Vishnu Priyan Rangasamy Apr 06 '16 at 12:35
Are you sure about that? The runtime error implies the type is a `java.lang.Long`. – Bathsheba Apr 06 '16 at 12:39
Yes I'm sure. I have verified that query.firstRow() gives a value of Object datatype – Vishnu Priyan Rangasamy Apr 06 '16 at 12:41
@VishnuPriyanRangasamy You'll need to cast it to a `Long`, and then use `BigInteger.valueOf` on that. – Louis Wasserman Apr 06 '16 at 17:11
@LouisWasserman How can the exception show 'Long' can not be cast, when the method returns 'Object' type? – Anmol Gupta Apr 06 '16 at 17:22
1

@Anmol the method return type is `Object`, but the actual runtime type is `Long`. This is _easy_ to reproduce: write `Object o = Long.valueOf(2); System.out.println(BigInteger.valueOf((Long) o));` – Louis Wasserman Apr 06 '16 at 17:23
Yes, I see that. Thanks! – Anmol Gupta Apr 06 '16 at 17:25

score 1 · Answer 2 · edited May 23 '17 at 10:28

Long is not a subclass of BigInteger, so 'Long is NOT BigInteger'. So, your Long can not be cast to a BigInteger.

https://docs.oracle.com/javase/7/docs/api/java/math/BigInteger.html

https://docs.oracle.com/javase/7/docs/api/java/lang/Long.html

Use static method of BigInteger: BigInteger.valueOf(long val); as BigInteger.valueOf(query.firstRow()).

And your code works in case of zero results because, you have initialized the count with a ZERO of type BigInteger. So, in case of zero results, your code does not get into the if statement (no casting is tried) and returns count straight away.

You might also want to read about Upcasting and Downcasting in Java.

What is the difference between up-casting and down-casting with respect to class variable

score 1 · Answer 3 · answered Apr 06 '16 at 11:42

1

java.lang.Long and java.math.BigInteger are in a different hierarchies. They cannot be castes to each other. You can create new BigInteger by using static factory method:

BigInteger.valueOf(yourLong);

answered Apr 06 '16 at 11:42

Rudziankoŭ

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java.lang.Long cannot be cast to java.math.BigInteger

3 Answers3