0xCAFEBABE

0xCAFEBABE is the magic number at the beginning of Java class files. It consists of four bytes: CA FE BA BE, which, when read as a 32-bit big-endian unsigned integer, equals 0xCAFEBABE. This header identifies the file as a Java class file and helps detect misformatted or incompatible data. After this header, the file specifies minor_version and major_version, followed by the constant pool and the remainder of the class data.

In practice, the Java Virtual Machine and class loaders read the magic number early in the parsing process to validate the file and select the appropriate parser for the rest of the content. The magic value is part of the Java class file format specification and serves as a simple integrity and compatibility check.

Originating with early versions of Java, CAFEBABE has become a well-known symbol in the Java ecosystem. The name is a playful, memorable reference that has persisted in software culture as a canonical example of a file signature or magic number.

Because it functions as a header, 0xCAFEBABE helps tooling distinguish class files from other binary formats and aids in quick validation during loading, disassembly, or analysis. While primarily associated with Java, the string is sometimes used in other contexts as a test value or marker in binary data.

See also: Java class file format, magic number, class loader, JVM.