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About Mary Zheng

Mary has graduated from Mechanical Engineering department at ShangHai JiaoTong University. She also holds a Master degree in Computer Science from Webster University. During her studies she has been involved with a large number of projects ranging from programming and software engineering. She works as a senior Software Engineer in the telecommunications sector where she acts as a leader and works with others to design, implement, and monitor the software solution.

Java 16 New Features Tutorial

1. Introduction

Java 16 has a list of new features. In this tutorial, I will demonstrate the following new features:

  • Java language – add a new java.lang.record type and the instanceof the method supports pattern matching.
  • Java API – Stream API adds toList() and mapMulti() methods.

2. Technologies Used

The example code in this article was built and run using:

  • Java 16
  • Eclipse 4.19

3. Record

Java 16 language add a new record type that deals with immutable data and provides constructor, getters, toString, equals, and hashCode methods automatically. Here is the syntax:

$accessModifier record $recordName ($parameters){ $body }

  • $accessModifier – can be public, private, or protected.
  • $recordName – follows Java class naming rules.
  • $parameters – follows Java variable naming rules.

3.1 Simple Record

In this step, I will create a SimpleRecord type which has two fields: name and isDone.


package org.jcg.zheng.lang.demo;

 * record is new language type to deal with immutable data without any
 * boiler-plate code: constructor, access, toString, equals, and hashCode
public record SimpleRecord(String name, boolean isDone) {


As you seen in Figure 1, compiler automatically provides name(), isDone(), toString(), equals(), hashCode(). It eliminates the boiler-plate code.

Java 16 - generated methods
Figure 1 SimpleRecord’s Generated Methods

3.2 Complex Record

In this step, I will create a ComplexRecord which implements from two interfaces: AInterface and Serializable. It also contains a SimpleRecord and validates the data.


package org.jcg.zheng.lang.demo;

import java.io.Serializable;
import java.util.Objects;

public record ComplexRecord(String title, String alias, int age, SimpleRecord simpleRecord)
		implements AInterface, Serializable {

	//can have static fields
	static String department = "Math";

	public String whoAreyou() {
		return "I am ComplexRecord. " + toString();

	//create a new access
	public String completedName() {
		return title + " " + alias;

	//override the generated getter
	public String title() {
		return title.toUpperCase();

	//overwrite constructor with validation
	public ComplexRecord {
		if (age < 0) {
			throw new IllegalArgumentException("age must be a positive number.");



  • line 10 – adds a static field.
  • line 18 – creates a new method transforming the data.
  • line 23 – overwrites the generated method.
  • line 28 – creates a constructor with validation logic.

Here is the interface which ComplexRecord implements.


package org.jcg.zheng.lang.demo;

public interface AInterface {
	String whoAreyou();


3.3 Demo Record

In this step, I will create a RecordDemoApp class which shows the usage of the SimpleRecord and ComplexRecord.


package org.jcg.zheng.lang.demo;

import java.util.HashMap;
import java.util.Map;

public class DemoRecordApp {

	public static void main(String[] args) {
		SimpleRecord simpleRed = new SimpleRecord("English", false);

		ComplexRecord redComplex = new ComplexRecord("Manager", "bob", 12, simpleRed);

		Map<SimpleRecord, ComplexRecord> test = new HashMap<>();
		test.put(simpleRed, redComplex);
		System.out.println("test map value=" + test.get(simpleRed));

		try {
			ComplexRecord bad = new ComplexRecord("Dead", "People", -5, simpleRed);
		} catch (Exception e) {


Execute it as a Java application and capture the output here.

RecordDemoApp output

ComplexRecord[title=Manager, alias=bob, age=12, simpleRecord=SimpleRecord[name=English, isDone=false]]
Manager bob
I am ComplexRecord. ComplexRecord[title=Manager, alias=bob, age=12, simpleRecord=SimpleRecord[name=English, isDone=false]]
test map value=ComplexRecord[title=Manager, alias=bob, age=12, simpleRecord=SimpleRecord[name=English, isDone=false]]
age must be a positive number.

4. Pattern Matching for instanceof

Pattern matching eliminates object cast when using the instanceof method. In this step, I will create an InstanceofDemo class to show the Java 16 and older way of the instanceof method.


package org.jcg.zheng.lang.demo;

public class InstanceofDemo {

	public static void main(String[] args) {



	private static void instanceOfMethod16(Object obj) {
		if (obj instanceof String s) {
			System.out.println("It's a string " + s);
		} else if (obj instanceof Integer i) {
			System.out.println("It's a number " + i);
			// System.out.println("can not see variable s here " + s);

	private static void instanceOfMethod(Object obj) {
		if (obj instanceof String) {
			String s = (String) obj;
			System.out.println("It's a string " + s);
		} else {
			System.out.println("It's not a string ");


	private static void instanceOfMethod16Else(Object obj) {
		if (!(obj instanceof String s)) {
			System.out.println("It's not a string ");
		} else {
			System.out.println("It's a string " + s);


  • line 17, 21 – can not access the variable s in the else block.
  • line 36, 39 – can access the variable s in the else block

Execute it as a Java application and capture output here.

InstanceofDemo output

It's a string Zheng
It's not a string 
It's a string Mary
It's a number 50
It's a string JCG
It's not a string 

5. Stream API

Java 16 enhances Stream API with toList() and mapMulti() methods. Developers can write less code when converting the stream to a list.

See Figure 2 for the detail of Stream.toList().

Java 16 - stream to list
Figure 2 Stream toList Method

See Figure 3 for the detail of Stream.mapMulti().

Java 16 - stream.mapmulti
Figure 3 Stream.mapMulti Method

In this step, I will create a StreamDemo class which uses both toList and mapMulti methods.


package org.jcg.zheng.api.demo;

import java.util.List;
import java.util.stream.Collectors;

public class StreamDemo {

	public static void main(String[] args) {

		List<String> testList = List.of("mary", "zheng", "Test");



		testList.stream().mapMulti((name, downstream) -> downstream.accept(name.replace("a", "-Number1-")))

	private static void StreamToList(List<String> testList) {
		List<String> immutableList = testList.stream().filter(name -> name.contains("e")).toList();
		try {
		} catch (Exception e) {
			// java.lang.UnsupportedOperationException as this containsAList is immutable

	private static void CollectorToList(List<String> testList) {
		List<String> mutableList = testList.stream().filter(name -> name.contains("e")).collect(Collectors.toList());



  • line 24 – Stream.toList() returns a unmodified list, so can not add a new element.

Run it as a Java application and capture the output here.

StreamDemo output

[zheng, Test, JCG]
[zheng, Test]
	at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:142)
	at java.base/java.util.ImmutableCollections$AbstractImmutableCollection.add(ImmutableCollections.java:147)
	at org.jcg.zheng.api.demo.StreamDemo.StreamToList(StreamDemo.java:24)
	at org.jcg.zheng.api.demo.StreamDemo.main(StreamDemo.java:14)

6. Summary

In this example, I demonstrated the following new features in Java 16 language and API:

  • Java language introduces a new record type.
  • Pattern matching with the instanceof method.
  • Stream has several new methods: toList() and mapMulti().

8. Download the Source Code

You can download the full source code of this example here: Java 16 New Features Tutorial

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