New Features In Java 19

Java 19 Features

Java 19 is released on 20 September 2022. One of the most exciting features of Java 19 is virtual threads. It is a prerequisite for structured concurrency.

Methods To Create Preallocated HashMaps

We can create an ArrayList of a known number of elements. But it is not the case in hashmap, because the default load factor of hashmap is 0.75. As soon as the hashmap is 75% full, it is rehashed with double size. So, if we want to create a hashmap of a known number, we have to calculate the capacity by diving the number with the load factor.

So, the HashMap of 100 mappings is created as follows:

120 / 0.75 = 160

Map map = new HashMap(160);

In Java 19, we can write as follows:

Map map = HashMap.newHashMap(120);

Pattern Matching For The Switch

In Java 19, the syntax of pattern matching for the switch is changed. Instead of && operator, we use the new keyword ‘when’. When is called a contextual keyword?

Record Pattern

Records in Java are introduced in the previous version. But in Java 19, instead of matching ‘Position position’ and accessing ‘position’ in the code, we can match ‘Position( int x, int y)’ and access ‘x’ and ‘y ‘directly.

Virtual Threads

Virtual threads are like normal threads from the Java perspective but they are not mapped with an operating system thread. Instead, they are pooled on carrier thread. As soon as the virtual thread encounters a blocking operation it is removed from the carrier thread and then the carrier thread executes another virtual thread. Thus no longer block the executing thread and allows multiple requests in parallel.

Deprecation and Degradation

• Locale class is marked as deprecated instead we use new static factory memory Locale.of.

• ThreadGroup.destroy().

• ThreadGroup.isDestroyed().

• ThreadGroup.setDaemon().

• ThreadGroup.getDaemon().

• ThreadGroup.suspend(), resume() and stop() throw UnsupportedOperationException.