Unlock Java 17: Records, Sealed Classes, Pattern Matching & More
This article explains why upgrading from Java 8 to JDK 17 is essential, detailing new language features such as records, sealed classes, pattern matching, text blocks, var inference, enhanced switch, Stream API improvements, better NullPointerExceptions, modern garbage collectors, and the foreign memory access API, all illustrated with concise code examples.
Are you still coding with Java 8? It's time to upgrade to JDK 17, a long‑term support release that brings a suite of powerful language features, making Java code more concise and efficient.
From JDK 8 to JDK 17
Why JDK 17 is a milestone
JDK 17 is the next LTS after JDK 8 and 11, integrating all innovations since JDK 9 and marking a major step in Java modernization.
Significance of LTS
As an LTS version, JDK 17 receives at least eight years of support, allowing enterprises to migrate confidently without frequent upgrades.
Record classes
Problems with traditional JavaBeans
Creating a simple data class traditionally requires boilerplate code for fields, constructors, getters, equals, hashCode, and toString.
public class Person {
private final String name;
private final int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() { return name; }
public int getAge() { return age; }
@Override
public boolean equals(Object o) { /* long implementation */ }
@Override
public int hashCode() { /* long implementation */ }
@Override
public String toString() { return "Person[name=" + name + ", age=" + age + "]"; }
}Record classes eliminate this boilerplate.
Basic syntax and usage
public record Person(String name, int age) {}The compiler automatically generates constructor, accessor methods, equals, hashCode, and toString.
Record and immutability
Records are immutable; to modify a value you create a new instance.
Person alice = new Person("Alice", 25);
Person olderAlice = new Person(alice.name(), alice.age() + 1);When to use records
Ideal for DTOs, value objects, or immutable containers. Not suitable when inheritance, additional fields, or abstract behavior is required.
Sealed classes
Core concept
Sealed classes allow a class to restrict which other classes may extend it, providing a middle ground between final and open inheritance.
public sealed class Shape permits Circle, Rectangle, Triangle {}permits keyword details
Subclasses must be declared final, sealed, or non‑sealed.
public final class Circle extends Shape { }
public sealed class Rectangle extends Shape permits Square { }
public non-sealed class Triangle extends Shape { }Combining with interfaces
public sealed interface Vehicle permits Car, Truck, Motorcycle {
void move();
}Practical use case
Sealed hierarchies are useful for domain modeling where the set of subtypes is closed.
public sealed interface PaymentMethod permits CreditCard, DebitCard, BankTransfer, DigitalWallet {
boolean processPayment(double amount);
}
public final class CreditCard implements PaymentMethod {
@Override
public boolean processPayment(double amount) { return true; }
}Pattern matching
Type pattern matching
Before JDK 17, instanceof required a separate cast; JDK 17 allows variable binding directly.
// Old way
if (obj instanceof String) {
String s = (String) obj;
if (s.length() > 5) { /* use s */ }
}
// New way
if (obj instanceof String s && s.length() > 5) {
// use s directly
}Switch expression enhancements
Switch can now pattern‑match and return a value.
String result = switch (obj) {
case Integer i -> "Integer: " + i;
case String s -> "String: " + s;
case Person p -> "Person: " + p.name();
default -> "Unknown type";
};Pattern matching can also improve performance by reducing redundant checks.
Text blocks
Problems with traditional string concatenation
Multi‑line strings required cumbersome concatenation and escaping.
String html = "<html>
" +
" <body>
" +
" <h1>Hello, World!</h1>
" +
" </body>
" +
"</html>";Text block syntax
String html = """
<html>
<body>
<h1>Hello, World!</h1>
</body>
</html>
""";Text blocks preserve line breaks and quotes without escaping.
Formatting tricks
Use \s to keep trailing spaces or backticks to concatenate lines.
String query = """
SELECT id, name, email \
FROM users \
WHERE status = 'ACTIVE' \
ORDER BY name
""";var and enhanced switch
Type inference benefits
var reduces verbosity when the type is evident.
var groupedPeople = new HashMap<String, List<Person>>();Switch as an expression with yield
String day = switch (dayOfWeek) {
case 1 -> "Monday";
case 2 -> "Tuesday";
case 3 -> "Wednesday";
case 4 -> "Thursday";
case 5 -> "Friday";
case 6, 7 -> "Weekend";
default -> "Invalid";
};Complex logic can use a block with yield.
String result = switch (status) {
case "PENDING" -> {
log.info("Processing pending");
yield "Processing";
}
case "APPROVED" -> {
log.info("Processing approved");
yield "Completed";
}
default -> "Unknown";
};Other useful features
Private interface methods
public interface Logger {
default void logInfo(String msg) { log(msg, "INFO"); }
default void logError(String msg) { log(msg, "ERROR"); }
private void log(String msg, String level) {
System.out.println("[" + level + "] " + msg);
}
}Stream API improvements
List<String> names = people.stream()
.map(Person::name)
.filter(name -> name.startsWith("张"))
.toList();
List<String> words = sentences.stream()
.mapMulti((s, c) -> {
for (String w : s.split(" ")) c.accept(w);
})
.toList();Enhanced NullPointerException
JDK 17 reports the exact variable that is null, e.g., "Cannot invoke Person.getName() because 'person' is null".
New garbage collectors
ZGC provides low‑pause (<10 ms) collection for terabyte‑scale heaps.
-XX:+UseZGCForeign memory access API
try (MemorySegment segment = MemorySegment.allocateNative(100)) {
MemoryAccess.setInt(segment, 0, 42);
int value = MemoryAccess.getInt(segment, 0);
System.out.println(value); // prints 42
}These APIs enable safe off‑heap memory manipulation.
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