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README.md

Java 24

To run each example use: java --enable-preview --source 24 <FileName.java>

JEPs

  • 472 - Prepare to Restrict the Use of JNI
  • 475 - Late Barrier Expansion for G1
  • 484 - Class-File API
  • 485 - Steam Gatherers
  • 489 - Vector API (Ninth Incubator)
  • 490 - ZGC Remove the Non-Generational Mode

Features

  • Prepare to Restrict the Use of JNI
    • align the command-line options to be used equally between JNI and FFM API
    • align how FFM API restrict the native method usage with warning instead of throwing an exception
      • JNI shows warnings unless --illegal-native-access=deny is provided
    • to use the previous behave we need to provide the following command-line options:
      • --enable-native-access=MyModule --illegal-native-access=deny
      • --illegal-native-access=warn is the default mode, in the future will be deny
      • this ways it will thrown an exception
    • added new JDK tool jnativescan to help identify the use of restricted methods and declarations of native methods
  • Late Barrier Expansion for G1
    • reduce the overhead of C2 JIT compiler
    • reduce the execution time of C2 when using G1
  • Class-File API
    • provide standard API for parsing, generating and modifying Java class file
    • provide standard API that is up to date with the features from current JDK released
    • design goals:
      • class-file entities are represented by immutable objects
      • tree-structured representation (e.g.: class is represented by ClassModel and can contain MethodModel, FieldModel, etc)
      • user-driven navigation
      • laziness when parsing class
      • unified streaming and materialized views
      • emergent transformation (transformation can be viewed as a flat-map operation)
      • detail hiding (constant pool, block scoping, stack maps, labels, variables index offset, etc)
    • API java.lang.classfile defines three main abstractions:
      • element: immutable description of some part of class file (instruction, attribute, field, method or an entire class)
      • builder: each compound element has a builder with methods to help construct the element
      • transform: represents a function that takes an element and a builder and mediates how that element is transformed (replaced, droped or passed to another builder)
    • we can iterate, transform or build elements using streams and Lambdas
    • we can use transformClass, transformMethod and transformCode to transform an element
    • to read a classe we must use ClassFile:
      • ClassModel cm = ClassFile.of().parse(bytes);
    • ClassFile is an iterable where we can navigates all its elements (fields, methods, etc) using pattern matching (instead of visitor in other libs): * 
      ClassModel cm = ClassFile.of().parse(bytes);
for (ClassElement ce : cm) {
    case FieldModel fm -> System.out.println("Field " + mm.methodName().stringValue());
    case MethodModel mm -> System.out.println("Method " + mm.methodName().stringValue());
    default -> System.out.println("Other " + ce);
}
    • ClassFile also provides methods to access the elements we need (parsing only the part need to get the methods): * 
      ClassModel cm = ClassFile.of().parse(bytes);
for (FieldModel fm : cm.fields()) {
    System.out.println("Field " + mm.methodName().stringValue());
}
for (MethodModel mm : cm.methods()) {
    System.out.println("Method " + mm.methodName().stringValue());
}

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