![]() import java.util.* īigDecimal bigDecimalArray = new BigDecimal īigDecimalArray = (BigDecimal) numberArray īigInteger bigIntegerArray = (BigInteger) numberArray /* Fails at runtime. They’re both “equally ranked” subtypes of Number. Note that BigDecimal and BigInteger are “siblings”, so neither is a subtype of the other. Instead of the abstract types Super and Sub, I will use the concrete classes Number as the supertype and BigDecimal and BigInteger as the subtype for this and all upcoming examples in this blog post. In order to answer the question for arrays (question 1), please have a look at the following example program. If Super is a superclass of Sub (i.e., Sub is a subclass of Super), then … The same applies to generic collections, e.g., List, where List is the complex type, and String is the type of its components. So an array, e.g., String, is a complex type, whereas String is its component type. By “more complex types”, we speak of arrays and generic collections here. ![]() the adjectives invariant and covariant (and also contravariant if one has a closer look at this topic), “refer to how subtyping between more complex types relates to subtyping between their components”, according to Wikipedia. The first principle one needs to know in order to understand the problem mentioned above is the fundamental difference between arrays and generics when it comes to variance. Arrays Versus Generics With Respect to Variance Shouldn’t generics-introduced in Java 5-allow the use of type parameters everywhere? Why is List genericList = new ArrayList() legal, but T genericArray = new T is not? This blog post answers these questions and shows several fixes to solve this problem. I bet that most Java programmers fall into the trap of trying to create generic arrays at least once in their Java software development career, wondering why the compiler is complaining.
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