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| evolving_java-based_apis [2014/02/06 07:57] – yann | evolving_java-based_apis [2025/01/15 21:40] (current) – external edit 127.0.0.1 |
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| Also, the document provides the simplest, clearest explanation of Java 1.5+ type erasure mechanism, that I reproduce here for the sake of beauty: | Also, the document provides the simplest, clearest explanation of Java 1.5+ type erasure mechanism, that I reproduce here for the sake of beauty: |
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| A raw type is a use of a generic type without the normal type arguments. For example, "List" in the declaration statement "List x = null;" is a raw type since List is a generic type declared "public interface List<E> ..." in JDK 1.5. Contrast this to a normal use of List which looks like "List<String> x = null;" or "List<?> x = null;" where a type augument ("String") or wildcard is specified. | >> A raw type is a use of a generic type without the normal type arguments. For example, "List" in the declaration statement "List x = null;" is a raw type since List is a generic type declared "public interface List<E> ..." in JDK 1.5. Contrast this to a normal use of List which looks like "List<String> x = null;" or "List<?> x = null;" where a type augument ("String") or wildcard is specified. |
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| The term erasure is suggestive. Imagine going through your code and literally erasing the type parameters from the generic type declaration (e.g., erasing the "<E>" in "public interface List<E> ...") to get a non-generic type declaration, and replacing all occurrence of the deleted type variable with Object. For type parameters with type bounds (e.g., "<E extends T1 & T2 & T3 & ...>"), the leftmost type bound ("T1"), rather than Object, is substituted for the type variable. The resulting declaration is known as the erasure. | >> The term erasure is suggestive. Imagine going through your code and literally erasing the type parameters from the generic type declaration (e.g., erasing the "<E>" in "public interface List<E> ...") to get a non-generic type declaration, and replacing all occurrence of the deleted type variable with Object. For type parameters with type bounds (e.g., "<E extends T1 & T2 & T3 & ...>"), the leftmost type bound ("T1"), rather than Object, is substituted for the type variable. The resulting declaration is known as the erasure." |
