* Java 18.

* Add README file.
* Remove source restriction from build gradle, upgrade version.
* Dominance Checking and Same-Type Patterns
* Exhaustiveness in Switch Expressions
* Internet Address Resolution SPI (JEP 418)

Author: jhon0010

build.gradle

@@ -3,11 +3,6 @@ plugins {
     id 'io.spring.dependency-management' version '1.0.1.RELEASE'
 }
 
-java {
-    sourceCompatibility = JavaVersion.VERSION_17
-    targetCompatibility = JavaVersion.VERSION_17
-}
-
 group 'org.example'
 version '1.0-SNAPSHOT'
 
@@ -17,7 +12,7 @@ repositories {
 
 dependencies {
     implementation 'org.projectlombok:lombok:1.18.22'
-    implementation 'org.json:json:20210307'
+    implementation 'org.json:json:20231013'
     annotationProcessor 'org.projectlombok:lombok:1.18.22'
 }
 

src/main/java/features_versions/eighteen_18/README.md

@@ -1,10 +1,22 @@
-# Java 18
+# Java 18 Features Summary
 
-
-## Features
-
-- **Pattern Matching for Switch**: Enhancements in pattern matching with switch.
-- **Improvements to Javac Compiler**: Better compiler checks and warnings.
-- **Code Snippets in Java API Documentation**: Including examples in Javadoc.
-- **String Deduplication**: For reducing memory usage.
-- **Finalization Deprecated for Removal**: Moving away from finalizers.
+1. JEP 400: UTF-8 by Default
+   Changes the default charset of the Java SE Platform to UTF-8, standardizing character encoding and simplifying internationalization.
+2. JEP 408: Simple Web Server
+   Introduces a command-line tool to start a minimal HTTP server that serves static files, designed for testing, development, and debugging purposes.
+3. JEP 413: Code Snippets in Java API Documentation
+   Enhances JavaDoc to support code snippets, ensuring they are automatically validated to improve API documentation quality.
+4. JEP 417: Vector API (Third Incubator)
+   Continues to incubate the Vector API, enabling reliable runtime compilation to optimal vector instructions, improving performance for vectorizable computations.
+5. JEP 418: Internet-Address Resolution SPI
+   Introduces a service provider interface for host name and address resolution, allowing for customized resolution strategies and better integration with different network environments.
+6. JEP 419: Foreign Function & Memory API (Second Incubator)
+   Advances the Foreign Function & Memory API, part of Project Panama, to improve Java's interoperation with native code and memory.
+   ## Focused Topics
+7. 
+   #### Dominance Checking and Same-Type Patterns
+   While not directly mentioned as a feature or JEP in Java 18, the concept of dominance checking and same-type patterns may relate to enhancements in pattern matching (for instanceof and possibly in switch expressions) and record patterns in Java. Dominance checking ensures that pattern matching in switch expressions is exhaustive and unambiguous. However, specific enhancements regarding "DominanceCheckingSameType" as a feature might not be directly addressed in Java 18 but are part of ongoing improvements in pattern matching and type checking in the Java language.
+   #### Exhaustiveness in Switch Expressions
+   Java has been enhancing switch expressions to support pattern matching. Exhaustiveness checking in switch expressions ensures that all possible cases are handled or a default case is provided. This feature was introduced to make switch expressions and pattern matching more robust and safer, preventing runtime errors due to unhandled cases.
+   #### Internet Address Resolution SPI (JEP 418)
+   This service provider interface (SPI) allows Java applications to customize how host names and IP addresses are resolved. It enables the replacement of the built-in address resolution mechanism with custom implementations, which can be crucial for applications running in environments with specific networking requirements or policies.

src/main/java/features_versions/eighteen_18/base/DominanceCheckingSameType.java

@@ -0,0 +1,23 @@
+package features_versions.eighteen_18.base;
+
+/**
+ * Review the below switch pattern matching, every value that matches the String s also matches the CharSequence cs,
+ * which makes String s unreadable and will cause a compile-time error.
+ */
+public class DominanceCheckingSameType {
+
+    static void error (Object o){
+        switch (o) {
+            case CharSequence cs -> System.out.println("A sequence of length " + cs.length());
+            /*
+             //Compile time Error - pattern is dominated by previous pattern doesn't happen before could lead to a bug
+            case String s ->
+                    System.out.println("A string: " + s);
+             */
+            default -> {
+                break;
+            }
+        }
+    }
+
+}

src/main/java/features_versions/eighteen_18/base/ExhaustivenessSwitchExpressions.java

@@ -0,0 +1,29 @@
+package features_versions.eighteen_18.base;
+
+/**
+ * The switch expression requires all possible values to
+ * be handled in the switch block, else prompts a compile-time error.
+ */
+public class ExhaustivenessSwitchExpressions {
+
+    public static void main(String[] args) {
+        coverage("Hello");
+    }
+
+    static int coverage(Object o) {
+        /**
+         // Error - not exhaustive switch expression, force you to implement default case or all possible values.
+         return switch (o) {
+         case String s  -> s.length();
+         case Integer i -> i;
+         };*/
+
+        return switch (o) {
+            case String s -> s.length();
+            case Integer i -> i;
+            default -> -1;
+        };
+    }
+
+
+}

src/main/java/features_versions/eighteen_18/base/InternetAddressResolutionSPI.java

@@ -0,0 +1,22 @@
+package features_versions.eighteen_18.base;
+
+import java.net.InetAddress;
+import java.net.UnknownHostException;
+
+/**
+ * JEP 400: Internet Address Resolution SPI
+ * By default, the java.net.InetAddress API uses the operating system’s built-in resolver to resolve host names to
+ * Internet Protocol (IP) addresses.
+ */
+public class InternetAddressResolutionSPI {
+
+    public static void main(String[] args) throws UnknownHostException {
+
+        InetAddress ip = InetAddress.getByName("google.com");
+        System.out.println("Host Name: " + ip.getHostName() + " IP Address: " + ip.getHostAddress());
+
+
+
+    }
+
+}