Was there ever a “change” in the Java language specification?

Question

With the likely widely known exception to the introduction of the 'assert' keyword, has there ever been a change in the specification of the Java language, which is why the old code is no longer compatible with newer levels of the JDK source code?

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Summary so far (many thanks for the comments):

Old Java codes can cause compiler errors when it uses declarations using one of the keywords introduced in a later version of the Java Language Specification (JLS):

• claim
• transfer
• strictfp

Answer 1

Java 1.2

• strictfp .

Java 1.4

• assert .

Java 1.5

• enum .

Answer 2

I believe that _ was designated as a "keyword" in Java 9. See https://blogs.oracle.com/sundararajan/underscore-is-a-keyword-in-java-9%2c-use-this- script-to-check-your-code

Answer 3

Java 10 made the var keyword. It is still a valid variable name, but an invalid class name.