1.5 did introduce at least one major backwards incompatible change. A new keyword which meant any variables named enum now broke the app. Installing a new Java

1.5 did introduce at least one major backwards incompatible change. A new keyword which meant any variables named enum now broke the app. Installing a new Java version on your desktop to run some app is different than rolling out a new major version of JVM/language for an enterprise application. There is a lot that went into ensuring everything still worked, including all dependencies, and that performance was acceptable. Maybe heap options needed to be changed because of how GC changed.