Update Java version requirement to JDK 21

- Bump Maven compiler properties from Java 11 to 21 in pom.xml
- Update README.md to require Java 21 or higher
- Modernize installation examples to use Java 21

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

2 files changed, 6 insertions, 6 deletions

diff --git a/README.md b/README.md
index 398083d..aadfc1b 100644
--- a/README.md
+++ b/README.md
@@ -14,7 +14,7 @@ DS-Sim is a modern, open-source simulator for distributed systems, written in Ja
 
 ## Requirements
 
-- Java 11 or higher
+- Java 21 or higher
 - Maven 3.8 or higher
 
 ### Setting up JAVA_HOME on Fedora Linux
@@ -36,8 +36,8 @@ alternatives --display java
 # Set JAVA_HOME to the current Java installation
 export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
 
-# Or for Java 11 if you have it installed
-export JAVA_HOME=/usr/lib/jvm/java-11-openjdk
+# Or for Java 21 if you have it installed
+export JAVA_HOME=/usr/lib/jvm/java-21-openjdk
 ```
 
 #### Method 3: Permanent Setup
@@ -58,8 +58,8 @@ java -version
 # Install OpenJDK 21 (recommended)
 sudo dnf install java-21-openjdk-devel
 
-# Or install OpenJDK 11 (minimum requirement)
-sudo dnf install java-11-openjdk-devel
+# Or install OpenJDK 17 (if you need older LTS version)
+sudo dnf install java-17-openjdk-devel
 
 # Install Maven
 sudo dnf install maven
diff --git a/pom.xml b/pom.xml
index 2d934f0..cdffe35 100644
--- a/pom.xml
+++ b/pom.xml
@@ -12,7 +12,7 @@
     <description>Distributed Systems Simulator - A modern Java-based simulator for distributed systems</description>
     
     <properties>
-        <java.version>11</java.version>
+        <java.version>21</java.version>
         <maven.compiler.source>${java.version}</maven.compiler.source>
         <maven.compiler.target>${java.version}</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>