https://www.graalvm.org/ 
class com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference extends java.lang.ref.WeakReference<com.oracle.truffle.polyglot.PolyglotContextImpl>
  minor version: 0
  major version: 59
  flags: flags: (0x0020) ACC_SUPER
  this_class: com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference
  super_class: java.lang.ref.WeakReference
{
  volatile boolean removed;
    descriptor: Z
    flags: (0x0040) ACC_VOLATILE

  final java.util.List<com.oracle.truffle.polyglot.PolyglotLanguageInstance> freeInstances;
    descriptor: Ljava/util/List;
    flags: (0x0010) ACC_FINAL
    Signature: Ljava/util/List<Lcom/oracle/truffle/polyglot/PolyglotLanguageInstance;>;

  void <init>(com.oracle.truffle.polyglot.PolyglotContextImpl);
    descriptor: (Lcom/oracle/truffle/polyglot/PolyglotContextImpl;)V
    flags: (0x0000) 
    Code:
      stack=3, locals=2, args_size=2
        start local 0 // com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference this
        start local 1 // com.oracle.truffle.polyglot.PolyglotContextImpl referent
         0: .line 1930
            aload 0 /* this */
            aload 1 /* referent */
            aload 1 /* referent */
            getfield com.oracle.truffle.polyglot.PolyglotContextImpl.engine:Lcom/oracle/truffle/polyglot/PolyglotEngineImpl;
            getfield com.oracle.truffle.polyglot.PolyglotEngineImpl.contextsReferenceQueue:Ljava/lang/ref/ReferenceQueue;
            invokespecial java.lang.ref.WeakReference.<init>:(Ljava/lang/Object;Ljava/lang/ref/ReferenceQueue;)V
         1: .line 1926
            aload 0 /* this */
            iconst_0
            putfield com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference.removed:Z
         2: .line 1927
            aload 0 /* this */
            new java.util.ArrayList
            dup
            invokespecial java.util.ArrayList.<init>:()V
            putfield com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference.freeInstances:Ljava/util/List;
         3: .line 1931
            return
        end local 1 // com.oracle.truffle.polyglot.PolyglotContextImpl referent
        end local 0 // com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference this
      LocalVariableTable:
        Start  End  Slot      Name  Signature
            0    4     0      this  Lcom/oracle/truffle/polyglot/PolyglotContextImpl$ContextWeakReference;
            0    4     1  referent  Lcom/oracle/truffle/polyglot/PolyglotContextImpl;
    MethodParameters:
          Name  Flags
      referent  
}
Signature: Ljava/lang/ref/WeakReference<Lcom/oracle/truffle/polyglot/PolyglotContextImpl;>;
SourceFile: "PolyglotContextImpl.java"
NestHost: com.oracle.truffle.polyglot.PolyglotContextImpl
InnerClasses:
  ContextWeakReference = com.oracle.truffle.polyglot.PolyglotContextImpl$ContextWeakReference of com.oracle.truffle.polyglot.PolyglotContextImpl