Question

I am getting the runtime error Exception in thread "main" java.lang.ClassCastException: m.compiler.datatypes.Int cannot be cast to java.lang.Integer

Here are the code snippets:

public abstract class DataType<E> {
protected E value;
...
}

And here the class Int:

public class Int extends DataType<Integer> {

@Override
public DataType<Integer> compare(DataType<Integer> other) {
    if(value > other.value) //here the exception is thrown
        return new Int(1);
    if (value < other.value)
        return new Int(-1);
    return new Int(0);
}

}

actual call:

        if(lValue instanceof Int) {
            Int lInt = (Int) lValue;
            Int result = (Int) lInt.compare(rInt);

if i print the values inside compare the values are right, but even if i check with

other.value.getClass()

i get the exception. compiler has no error and no warnings.

Answer 1

At some point, you must have assigned an Int to value… And there should have been a warning about that. Can you make value final?