What Changed in Java 21? Double/Float toString Precision and IdentityHashMap Bug Fixes

Double.toString() and Float.toString() precision fix

In Java 21, the precision issue of Double.toString() and Float.toString() has been fixed. For example, Double.toString(1e23) now produces the expected output.

In Java 19 and later, the output is: 1.0E23 In Java 18, the output was:

9.999999999999999E22

IdentityHashMap remove(key, value) and replace(key, value, newValue) error handling

IdentityHashMap

uses identity comparison (==) instead of equals() to determine key equality. Before Java 20, the remove(key, value) and replace(key, value, newValue) methods incorrectly compared the supplied value with the map’s stored value using equals(), leading to unexpected results.

Starting with Java 20, these methods correctly use identity comparison, so the operations behave as documented.

Example:

var users = new IdentityHashMap<String, User>();
String key = "abc";
users.put(key, new User("Jane Doe"));
var removed = users.remove(key, new User("Jane Doe"));
assert !removed;