1. Java does not allow to implement new interfaces for classes without modifying their signature - much more limiting than Rusts foreign trait rule. You cannot make a foreign class implement your new interface.
2. Java does not allow to create wrappers without incurring a significant memory overhead. A wrapper will consume at least 32 bytes of memory on 64-bit systems just for itself, when in Rust this can be 0.
3. Even if you define a wrapper, it would be way less ergonomic than in Rust - there is nothing like AsRef / Deref / From / Into etc machinery in Java.
Comments
1. Java does not allow to implement new interfaces for classes without modifying their signature - much more limiting than Rusts foreign trait rule. You cannot make a foreign class implement your new interface.
2. Java does not allow to create wrappers without incurring a significant memory overhead. A wrapper will consume at least 32 bytes of memory on 64-bit systems just for itself, when in Rust this can be 0.
3. Even if you define a wrapper, it would be way less ergonomic than in Rust - there is nothing like AsRef / Deref / From / Into etc machinery in Java.