ClassCastException
ClassCastException is a Java runtime exception thrown when a value cannot be cast to the requested reference type.
100 Java Mistakes and How to Avoid Them
ClassCastException is the Java runtime exception thrown when a value cannot be cast to the requested reference type, including when identically named classes come from different class loaders.
- How it is used
- Prevents fragile runtime conversions at API boundaries and in generic collections.
- How deep it goes
- Explains explicit checks and compiler-inserted generic casts down to runtime type erasure, while deferring pattern details to Java 16 references.
- Examples
- Uses Object-to-String processing, equals() casting, pattern instanceof, and a corrupted List<String> whose failure is delayed.
- What you can do after
- Diagnose/debug with it by locating unsafe explicit or erased generic conversions and replacing them with checked type contracts.
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Kotlin in Action, 2E
ClassCastException is a JVM runtime exception thrown when a value is used as an incompatible type.
- How it is used
- Explains why unchecked generic casts can defer type failures until values are consumed.
- How deep it goes
- Traces a cast from compiler warning through successful runtime check to failure during numeric summation.
- Examples
- Uses printSum with integer lists, integer sets, and string lists to contrast successful output and two exception paths.
- What you can do after
- Diagnose/debug unchecked generic casts by distinguishing failures at the cast boundary from failures during value use.
Related concepts
- data conversionproduced by · Data conversion is the transformation of a value or data from one type, format, or representation to another, explicitly or implicitly.
- as operatorproduced by · The as operator is language syntax that associates a value or expression with a specified type through assertion, casting, or conversion, depending on the language.
- exact-match accuracyproduced by · Exact-match accuracy evaluates outputs by whether they exactly equal their references under specified comparison rules.
- implicit conversionproduced by · Implicit conversion is an automatic change of a value from one type to another according to language rules, without an explicit conversion operation in the source code.
- raw typeproduced by · A raw type is a Java generic type used without specifying its type arguments, weakening compile-time type checking for that use.
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