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You get an error that says .size cannot be resolved because the Object class does not have a size variable visible to your class.

So long as aThat is of type object, aThat.size will not work. If...

What did you try casting to what and where in the code did that take place?

public boolean equals(Object aThat) { // aThat is a DynamicArrayOfInts object
if(this.size!=aThat.size) { //i...