Javadocs are interpreted as HTML, so special characters such as <, >, and & must be escaped.

Text within @code, @literal and @link tags is exempt from this.

/** Returns whether n > 3. */
boolean greaterThanThree(int n);

Could be rendered as one of these instead:

/** Returns whether n > 3. */
boolean greaterThanThree(int n);

/** Returns whether {@code n > 3}. */
boolean greaterThanThree(int n);

A common pitfall is type parameters. The following Javadoc is valid, but contains an unknown HTML tag (Integer):

/** Returns an Iterable<Integer> of prime numbers. */
Iterable<Integer> generatePrimes();

Prefer writing generic types as {@code Iterable<Integer>} (or {@link }).

Suppression

Suppress by applying @SuppressWarnings("UnescapedEntity") to the element being documented.