I am getting class cast exception at line 7 in the code below. I have written line 1-3 to provide data that comes from a rest service call and these line can’t be changed from my side. I must cast the response to List Answer Thank you @Michael. I had to run a getEntity on gEntity and then cast it
Tag: generics
incompatible types: int cannot be converted to T
I’m getting this error, here is the necessary code. Assume the methods not here work correctly. Any help would be awesome. (I am coding on a text file in Ubuntu btw) Here is the error message: (after compiling) BinarySearchTree.java:132: error: incompatible types: int cannot be converted to T insert(y);…
Java generics: Map nested json response to Java objects
Scenario: I’m working with an unusual external API in which every attribute is a map with multiple values. In order to convert this response into simple Java objects, I had to do some dirty unboxing. Below is one of the typical java class. As you can see how I’m unboxing data from response and map…
Why is this lambda expression cast using an ampersand?
recently I stumbled over the following code in the Java Comparator class: What’s confusing me is the (Comparator<T> & Serializable) part. Since the method only returns a Comparator I don’t see the use in casting to Serializable. I also don’t see the reason to ever cast anything thi…
Static method to count occurrences of a letter in a lower case word using maps
I have to create a class called MakeMap with a single static method called countLetters(). The method should take as a parameter a word formed of lowercase letters and return a map of the counts of …
How to resolve `Raw use of parameterized class ‘Comparable’` warning?
Got to implement the method below for an assignment which it’s subject is “WildCards”, but don’t know where to use wildcards in order to resolve the warning. Any ideas ? Answer Comparable is a generic interface, so to use it safely you must always specify the generic type to use. In yo…
Wildcard not allowed for Iterable in Java
I have following code setup. But this is not allowed as wildcard is not allowed for Iterable. What actually Java tries to a achieve here by not allowing this? What modifications would get this working? Answer When a class instance is created, it invokes the initializer of the super type. But you can’t u…
When building containers why is using Java Generics better than using the Object Class? (Java Generics & DataStructures)
So I have been reviewing my data structures and came across an interesting thought regarding Java generics and the Object class. I have implemented and run a “generic bag” in two different ways (Notice below: IObjectBag.java, ObjectBag.java, IGenericBag.java, and GenericBag.java) and have used the…
Mockito thenReturn returns null when coming from generic function
I want to mock the ResultSet in a class, whose parameters come from a generic return function (getSQLValue): The table class with the signature method: And this is the unit test class: The problem is that the ResultSet is always null, I can confirm when debugging. Answer Turns out that Mockito, after “a…
Best practice for using generics with Firebase snapshot.getValue()
TL;DR: How to correctly use a generic class with Firebase DataSnapshot.getValue()? Use case: I want to implement a single generic remote datasource class for all my entities (a bunch of them) using Firebase. When listening to data change, I want to get the values from datasnapshot as an object of type E (its …