java-28

Java 28

To run each example use: java --enable-preview --source 28 <FileName.java>

JEPs

• 401 - Value Objects (Preview)
• 535 - Shenandoah GC: Generational Mode by Default
• 539 - Strict Field Initialization in the JVM (Preview)
• 540 - Simple JSON API (Incubator)
• 541 - Deprecate the macOS/x64 Port for Removal
• 542 - PEM Encodings of Cryptographic Objects

Features

• Shenandoah GC: Generational Mode by Default
  • Shenandoah is a low-pause-time garbage collector
  • switch the default mode of Shenandoah GC to the generational mode
  • deprecate the non-generational mode
  • default mode: XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational
  • to use non-generational mode: -XX:+UseShenandoahGC -XX:ShenandoahGCMode=satb
• Simple JSON API
  • a simple standard API for parsing and generating JSON documents that conform to RFC 8259
  • this JEP replaces the JEP 198 - Light-Weight JSON API
  • the API is organized around the sealed interface JsonValue which has the following sub-interfaces: JsonString, JsonNumber, JsonBoolean, JsonNull, JsonObject and JsonArray
  • the Json.parse method returns a tree of JsonValue instances that expose the names, types, and values of the parsed JSON data
  • generating JSON text:
    • Json.toString: returns the JSON string converted from the tree of objects:
    • Json.toDisplayString(JsonValue, String): returns the formatted JSON string for better readability, the string parameter is the indentation
  • navigating JSON documents:
    • JsonValue methods to read a value:
      • get(String): obtains the value of an object member
      • get(int): obtains an array element
      • tryGet(String): obtains an optional value of an object member
    • it is recommended to use type patterns to handle dynamic structure
    • if the JsonValue instance is of the wrong type or the requested member or element does not exist a JsonValueException will be thrown
  • converting values to Java types:
    • JsonValue methods to convert a value:
      • asString
      • asInt
      • asLong()
      • asDouble()
      • asBoolean()
      • asMap()
      • asList()
    • the methods are implemented by the JsonValue sub-interfaces (JsonString, JsonNumber)
    • there is no conversion method for null value, we should check with instanceof JsonNull or use tryValue that returns an Optional
    • if a JsonValue is not an instance of the appropriate subtype for a conversion method then the method throws a JsonValueException
    • numeric conversions can fail for reasons such as the numeric value not being representable in the target Java numeric type, which also causes a JsonValueException to be thrown
• PEM Encodings of Cryptographic Objects
  • promotion to standard
  • "introduce an API for encoding objects that represent cryptographic keys, certificates, and certificate revocation lists into the widely-used Privacy-Enhanced Mail (PEM) transport format"
  • support conversions between PEM text and cryptographic objects that have standard representations in the binary formats of PKCS#8 (for private keys), X.509 (public keys, certificates, and certificate revocation lists), and PKCS#8 v2.0 (encrypted private keys and asymmetric keys)

Links

• JDK 28 JEPs
• JDK 28 - JEP Dashboard