Java 15 New Features
After looking into the new features in Java 14, let’s continue with my series of Java new features with Java 15.
JEP 360: Sealed Classes (Preview)
This is on preview, so to use it, you need to supply the --enable-preview when running Java. |
A sealed class or interface can be extended or implemented only by those classes and interfaces permitted to do so:
public abstract sealed class Shape permits Circle, Rectangle, Square {
public int getCenter(Shape shape) {
if (shape instanceof Circle) {
return ... ((Circle)shape).center() ...
} else if (shape instanceof Rectangle) {
return ... ((Rectangle)shape).length() ...
} else if (shape instanceof Square) {
return ... ((Square)shape).side() ...
}
}
}
Previously, without having declared the permits, we had to implement the getCenter method like:
int getCenter(Shape shape) {
if (shape instanceof Circle) {
return ... ((Circle)shape).center() ...
} else if (shape instanceof Rectangle) {
return ... ((Rectangle)shape).length() ...
} else if (shape instanceof Square) {
return ... ((Square)shape).side() ...
}
throw new RuntimeException("Unsupported!");
}
With sealed, we don’t need to throw any runtime exception because we’re only allowing the three types of shapes.
Another important point is that every permitted subclass must define a modifier:
- sealed: to declare that the class is an implementation.
- final: it’s like a strong sealed where we can’t reimplement the class.
- non-sealed: to say that the current class is still open to extension
More information about these changes in Baeldung.
JEP 384: Records (Second Preview)
This is on preview, so to use it, you need to supply the --enable-preview when running Java. |
This feature was entered in Java 14 as preview, and it’s improved here by allowing to extend the generated class, for example to redefine the default constructor:
public record Person(String name, int age) {
Person {
if (age < 18) {
throw new IllegalArgumentException("Too young!");
}
}
};
JEP 375: Pattern Matching for instanceof (Second Preview)
This is on preview, so to use it, you need to supply the --enable-preview when running Java. |
This feature was entered in Java 14 as preview, and it’s improved here by allowing to use the variable in the combined expression:
if (person instanceof Person person && person.getAge() > 23) {
//...
}
JEP 378: Text Blocks
This feature was entered in Java 13 and 14 as preview and it’s now officially supported. As a summary, we can write multiline text as:
String text = """
{
"name" : "Foo", \
"surname" : "Buu" \s
}
""";
JEP 371: Hidden Classes
Create classes that are intended to be used internally by frameworks via reflection:
import java.lang.invoke.MethodHandles;
import java.lang.reflect.Constructor;
import static java.lang.invoke.MethodHandles.Lookup.ClassOption.NESTMATE;
public class MyHiddenClass {
public static void main(String[] args) throws Throwable {
MethodHandles.Lookup lookup = MethodHandles.lookup();
ClassWriter cw = GenerateClass.getClassWriter(MyHiddenClass.class);
byte[] bytes = cw.toByteArray();
Class<?> c = lookup.defineHiddenClass(bytes, true, NESTMATE).lookupClass();
// ...
}
}