Seven Java library changes that compile and pass tests but break existing users

A DEV Community article lists seven library changes in Java that compile and pass the library's own tests yet still break its users. The author distinguishes source compatibility, whether callers' code still compiles, from binary compatibility, whether previously compiled code still runs against the new jar. Because applications often update a library without recompiling its dependents, binary compatibility is especially important. Each example is checked on Java 25 and shows the real error messages that result. The article suggests safer alternatives, such as adding overloads, keeping return types, or giving new interface methods default implementations.