Through Java's evolution keywords have been added. While code that uses those words as identifiers may be compilable under older versions of Java, it will not be under modern versions.

Keyword	Added
assert	1.4
const	reserved
enum	5.0
goto	reserved
strictfp	1.2

Noncompliant Code Example

public void doSomething() {
  int enum = 42;            // Noncompliant
}

Compliant Solution

public void doSomething() {
  int magic = 42;
}