java.lang.ClassCastException: java.util.HashSet incompatible with DTO

Question

public void write(List<? extends Set<DTO>> setOfDTO)
        throws Exception {

    if (!setOfDTO.isEmpty()) 
    {
        Map<BigInteger, String> tempMap = new HashMap<BigInteger, String>();
        for (DTO dto : setOfDTO.get(0)) {...}

Interesting part is, this does not happen always. So I was wondering if this has anything to do with compiler versions or some other factors. I am using Buildforge(Maven) to build these JARs

Answer 1

It should be:

public void write(List<? extends Set<DTO>> setOfDTO) throws Exception {
    if (!setOfDTO.isEmpty()) {
        Map<BigInteger, String> tempMap = new HashMap<BigInteger, String>();
        for (Set<DTO> dto : setOfDTO) {...}
    }
}

Your list contains Set<DTO> and not DTO objects.