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Java 16: An Introduction from a Java 8 Monogamist

Java 9 and 10

JShell: execute and experiment with Java code without creating a class or main method; those of you familiar with the Python shell will quickly be able to put this to good use

|  Welcome to JShell -- Version 9
|  For an introduction type: /help intro
jshell> "This is my long string. I want a part of it".substring(8,19);
$5 ==> "my long string"

.copyOf(): create an unmodifiable copy of lists, maps, and sets (modify throws exception)

List<Integer> copyList = List.copyOf(someIntList);
copyList.add(4); //throws exception

.toUnmodifable(): similar to copyOf(), but for stream collection

List<Integer> evenList =
  .filter(i -> i % 2 == 0)
evenList.add(4); //throws exception

.orElseThrow(): if no value is present for an optional, throw a specified exception

Integer firstEven =
  .filter(i -> i % 2 == 0)

var: new reserved type name, similar to its use in Scala; allows for type inference; must be initialized, and cannot be initialized to null (needed for compiler to determine what to do); only supported for local in-method variables

Map<Integer, String> map = new HashMap<>();
var idToNameMap = new HashMap<Integer, String>();

var message = "Hello, Java 10";
assertTrue(message instance of String);

Java 11

New helpful String methods: .isBlank() .lines() .strip() .stripLeading() .stripTrailing()

String multilineString = "I love \n \n Java 11 \n a lot.";
List<String> lines = multilineString.lines()
  .filter(line -> !line.isBlank())
assertThat(lines).containsExactly("I love", "Java 11", "a lot.");

.toArray(): simpler collection conversion to an array. Why is this useful? Arrays are of a fixed size, have better performance (although cost more memory), and can hold either objects or primitives

List sampleList = Arrays.asList("Java", "Kotlin");
String[] sampleArray = sampleList.toArray(String[]::new);

assertThat(sampleArray).containsExactly("Java", "Kotlin");

var now supported for lambda parameters: more readable than explicit type definition; allows for type annotations within streams

List<String> sampleList = Arrays.asList("Java", "Kotlin");
String resultString =
  .map((@Nonnull var x) -> x.toUpperCase())
  .collect(Collectors.joining(", "));
assertThat(resultString).isEqualTo("JAVA, KOTLIN");

Directly run java without javac compiling: allows for single file source code, without the need for pre-compilation

$ javac
$ java HelloWorld 
Hello Java 8!
$ java
Hello Java 11!

Java 12

New String methods: String .indent() and .transform()

String text = "Hello Ippon!\nThis is a Java 12 blog post.";

text = text.indent(4);
//prints this (with an indent of 4 spaces)
    Hello Ippon!
    This is a Java 12 blog post.
String text = "Hello Ippon!\nThis is a Java 12 blog post.";

text = text.indent(-10);
//prints this (with no indent)
Hello Ippon!
This is a Java 12 blog post.
String text = "Ippon";
String transformed = text.transform(value ->
      new StringBuilder(value).reverse().toString()

assertEquals("noppI", transformed);

Files package .mismatch() static method: will return -1 if two files are matching, or the index of the first differentiating byte; no more byte array comparisons!

Path filePath1 = Files.createTempFile("file1", ".txt");
Path filePath2 = Files.createTempFile("file2", ".txt");
Files.writeString(filePath1, "Java 12 Article");
Files.writeString(filePath2, "Java 12 Article");

long mismatch = Files.mismatch(filePath1, filePath2);
assertEquals(-1, mismatch);

CompactNumberFormat: convert numbers to strings based on patterns provided by a given locale

NumberFormat shortFormat = 
      NumberFormat.getCompactNumberInstance(new Locale("en", "US"), NumberFormat.Style.SHORT);
assertEquals("2.59K", shortFormat.format(2592));

NumberFormat longFormat = 
      NumberFormat.getCompactNumberInstance(new Locale("en", "US"), NumberFormat.Style.LONG);
assertEquals("2.59 thousand", longFormat.format(2592));

Java 13 and 14

Improved switch expression concision: we can now define multiple cases within a single line, without the need for breaks

boolean isTodayHoliday;
switch (day) {
    case "MONDAY":
    case "TUESDAY":
    case "WEDNESDAY":
    case "THURSDAY":
    case "FRIDAY":
        isTodayHoliday = false;
    case "SATURDAY":
    case "SUNDAY":
        isTodayHoliday = true;
        throw new IllegalArgumentException("What's a " + day);


boolean isTodayHoliday = switch (day) {
    case "MONDAY", "TUESDAY", "WEDNESDAY", "THURSDAY", "FRIDAY" -> false;
    case "SATURDAY", "SUNDAY" -> true;
    default -> throw new IllegalArgumentException("What's a " + day);

More helpful and descriptive Null Pointer Exceptions. I can already hear you quietly saying to yourself, "Finally!"

int[] arr = null;
arr[0] = 1;
Exception in thread "main" java.lang.NullPointerException
at com.baeldung.MyClass.main(


int[] arr = null;
arr[0] = 1;
java.lang.NullPointerException: Cannot store to int array because "a" is null

Java 15

Text blocks: Now fully supported as a production ready feature

String html = """
              		  <p>Hello World.</p>
String multiline = "A quick brown fox jumps over a lazy dog; the lazy dog howls loudly.";
String multiline = """
    A quick brown fox jumps over a lazy dog; \
    the lazy dog howls loudly.""";

Sealed classes: More control over and ability to be restrictive with inheritance; the below code will prevent any object other than Employee and Manager from ever extending Person

public abstract sealed class Person permits Employee, Manager {

public final class Employee extends Person {}

public non-sealed class Manager extends Person {}

//the below will not throw a warning, even without 
//a final 'else' condition, as the compiler can infer 
//from the sealed class definition that all possibilities 
//have been exhausted

if (person instanceof Employee) {
    return ((Employee) person).getEmployeeId();
else if (person instanceof Manager) {
    return ((Manager) person).getSupervisorId();

Java 16

Records: More concise definitions of immutable DTOs; compiler will also auto-provide toString, equals, and hashCode methods. (Note: while records were previewed in Java versions 14 and 15, Java 16 releases them as a production-ready feature)

//Immutable DTO Before
public class Person {
    private final String name;
    private final int age;

    public Person(String name, int age) { = name;
        this.age = age;

    public String getName() {
        return name;

    public int getAge() {
        return age;

//vs Immutable DTO After

public record Person(String name, int age) {}
public record Person(String name, int age) {
    public Person {
        if(age < 0) {
            throw new IllegalArgumentException("Age cannot be negative");

Pattern matching: Remove boilerplate code required for instanceof checks; you can now have pattern matching and conditionals within the same line of code. (Note: similar to Records, this was previewed in earlier versions, but is now a fully supported production-ready feature)

if (person instanceof Employee) {
    Employee employee = (Employee) person;
    Date hireDate = employee.getHireDate();


if (person instanceof Employee employee) {
    Date hireDate = employee.getHireDate();


if (person instanceof Employee employee && employee.getYearsOfService() > 5) {

You probably noticed that these updates don't appear to include all that many changes. This is both because Java releases now occur every 6 months, and that they tend to include mostly under-the-hood upgrades. For a more in-depth look at the differences between Java's LTS and non-LTS releases, see:

We hope that this introduction will allow for you to more quickly dive into post-Java 8 versions and use what they have to offer in your daily work. For more information regarding non-coding-related changes made in these updates, be sure to check out Oracle's very helpful JDK release notes library. Thanks for reading!


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Post by Mike Mitchell
Mar 26, 2021 11:40:00 AM


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