Which statement about generics is true?

Question

BlackTom AI · Accepted Answer

Generics provide compile-time type safety and let you parameterize classes, interfaces, and methods with types, so you can work with collections and other containers without doing explicit casts when retrieving elements. Relevant knowledge points and concepts - Generics = type parameters (e.g., List, Map) that enforce types at compile time. - They prevent accidental insertion of wrong types and remove the need for explicit casting on retrieval. - Java generics use type erasure at runtime, but that does not affect the compile-time benefits. - Limitations: Java generics do not accept primitive types directly (use wrapper classes), they are not limited to arrays, and they promote reuse rather than prevent it. Step-by-step reasoning with examples 1. Without generics: List list = new ArrayList(); list.add("hello"); String s = (String) list.get(0); // explicit cast required; unsafe at compile time 2. With generics: List list = new ArrayList<>(); list.add("hello"); String s = list.get(0); // no cast required; compiler knows elements are Strings Intermediate explanation - In the non-generic example, the compiler treats list.get(0) as Object, so you must cast; a wrong cast causes ClassCastException at runtime. - In the generic example, the compiler enforces the element type (String) and returns String from get(), eliminating the cast and catching type errors at compile time (e.g., list.add(123) would be a compile-time error). Why the correct answer is correct "Generics remove the need for casting" is correct because generics allow methods like get() to have a specific return type (List.get() returns String), so explicit casting is unnecessary and unsafe casts are avoided. Why the other options are incorrect - "Generics only work with arrays": false — generics work with classes, interfaces, methods and collections; arrays are separate and have their own type rules. - "Generics allow primitive types like int directly": false — Java generics require reference types; use Integer, Double, etc. - "Generics prevent classes from being reused": false — generics increase reusability by allowing a class to operate on multiple types safely. Conclusion The correct answer is "Generics remove the need for casting," which matches the provided answer.

Which statement about generics is true?单项选择题

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