Is this valid Java code: ArrayList nums = new List();

Question

Is this valid Java code: ArrayList nums = new List<>();

BlackTom AI · Accepted Answer

Question restatement: Is this valid Java code: ArrayList nums = new List<>(); Option 1: 'No, since 'new List<>();' should instead be 'new List();'" - This option points out a common syntax issue: trying to instantiate an interface (List) directly is illegal in Java. Even if you used generic type parameters, you cannot call new on an interface. While the suggestion to use 'new List()' would still be invalid because you cannot instantiate an interface at all, the core problem here is the attempted instantiation of List itself, not the missing type parameter. So this option partially identifies a problem but misstates the correct reasoning about interfaces vs. generics. Option 2: 'No, since 'ArrayList' should instead be 'ArrayList'' - This is incorrect because Java generics use reference types, not primitive types. You cannot parameterize with 'int'; you must use 'Integer'. The reasoning here conflates primitive specialization with generics, which makes this option factually wrong. Option 3: 'No, since List is an interface, and we cannot create objects from them.' - This correctly identifies the fundamental issue: List is an interface, and Java requires a concrete class instance on the right-hand side. You would typically instantiate a concrete implementation like 'new ArrayList<>()' and assign it to a variable of type List (e.g., List nums = new ArrayList<>();). This option captures the correct conceptual error: attempting to instantiate an interface. Option 4: 'Yes' - This is false because, as explained, the expression attempts to instantiate an interface (List) rather than a concrete class, and no valid compensation in the code makes it valid Java. Summary of reasoning across options: - The primary flaw in the code is attempting to 'new' an interface (List), which Java does not permit. Since the right-hand side should be a concrete class instance, Option 3 correctly identifies the structural problem. Option 2 misstates generics usage by suggesting a primitive type parameter, which Java does not allow in generics. Option 1 mentions the incorrect form 'new List()' but still centers on instantiating an interface, which is not possible; however, the gear of the explanation is mixed and not as precise as Option 3. Option 4 is simply incorrect because the code cannot compile as written.

Is this valid Java code: ArrayList<Integer> nums = new List<>();单项选择题

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