https://stackoverflow.com/questions/70358545/how-does-the-new-java-17-type-pattern-matching-switch-works-under-the-hood

public class Switch {
    public static void main(String args[]) {
        doit(args);
    }
    static void doit(Object o) {
        System.out.println(switch (o) {
            case String s -> "String";
            case String[] arr -> "String Array";
            default -> "Object";
            });
    }
}

******************************************************************************

$ javac --release 20 --enable-preview Switch.java 
$ javap -c Switch.class
Compiled from "Switch.java"
public class Switch {
  public Switch();
    Code:
       0: aload_0
       1: invokespecial #1                  // Method java/lang/Object."<init>":()V
       4: return

  public static void main(java.lang.String[]);
    Code:
       0: aload_0
       1: invokestatic  #7                  // Method doit:(Ljava/lang/Object;)V
       4: return

  static void doit(java.lang.Object);
    Code:
       0: getstatic     #13                 // Field java/lang/System.out:Ljava/io/PrintStream;
       3: aload_0
       4: dup
       5: invokestatic  #19                 // Method java/util/Objects.requireNonNull:(Ljava/lang/Object;)Ljava/lang/Object;
       8: pop
       9: astore_1
      10: iconst_0
      11: istore_2
      12: aload_1
      13: iload_2
      14: invokedynamic #25,  0             // InvokeDynamic #0:typeSwitch:(Ljava/lang/Object;I)I
      19: lookupswitch  { // 2
                     0: 44
                     1: 54
               default: 65
          }
      44: aload_1
      45: checkcast     #29                 // class java/lang/String
      48: astore_3
      49: ldc           #31                 // String String
      51: goto          67
      54: aload_1
      55: checkcast     #33                 // class "[Ljava/lang/String;"
      58: astore        4
      60: ldc           #35                 // String String Array
      62: goto          67
      65: ldc           #37                 // String Object
      67: invokevirtual #39                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
      70: return
}

**********************************************************************

$ java -Djava.lang.invoke.MethodHandle.TRACE_CALLSITE=true --enable-preview -cp . Switch
linkCallSite Switch.doit(Switch.java:6) java.lang.runtime.SwitchBootstraps.typeSwitch(Lookup,String,MethodType,Object[])CallSite/invokeStatic typeSwitch(Object,int)int/BSA=[class java.lang.String, class [Ljava.lang.String;]
linkMethod java.lang.invoke.MethodHandle.invokeExact(Lookup,String,MethodType,Object[])CallSite/5
linkMethod => java.lang.invoke.LambdaForm$MH/0x0000000801001000.invokeExact_MT000_LLLLLL_L(Object,Object,Object,Object,Object,Object)Object/invokeStatic + (Lookup,String,MethodType,Object[])CallSite
linkMethod java.lang.invoke.MethodHandle.invokeExact(Object)Object/5
linkMethod => java.lang.invoke.Invokers$Holder.invokeExact_MT(Object,Object,Object)Object/invokeStatic + (Object)Object
linkCallSite java.base/java.lang.runtime.SwitchBootstraps.typeSwitch(SwitchBootstraps.java:128) java.lang.invoke.LambdaMetafactory.metafactory(Lookup,String,MethodType,MethodType,MethodHandle,MethodType)CallSite/invokeStatic accept()Consumer/BSA=[(Object)void, MethodHandle(Object)void, (Object)void]
linkMethod java.lang.invoke.MethodHandle.invokeExact(Lookup,String,MethodType,MethodType,MethodHandle,MethodType)CallSite/5
linkMethod => java.lang.invoke.Invokers$Holder.invokeExact_MT(Object,Object,Object,Object,Object,Object,Object,Object)Object/invokeStatic + (Lookup,String,MethodType,MethodType,MethodHandle,MethodType)CallSite
linkMethod java.lang.invoke.MethodHandle.invokeExact()Object/5
linkMethod => java.lang.invoke.Invokers$Holder.invokeExact_MT(Object,Object)Object/invokeStatic + ()Object
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_L
linkCallSite target => ()Consumer : invoke001_L_L=Lambda(a0:L/SpeciesData[L => Species_L])=>{
    t1:L=Species_L.argL0(a0:L);t1:L}
& BMH=[
  0: ( java.lang.runtime.SwitchBootstraps$$Lambda$1/0x0000000801041558@73d16e93 )
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object)Object/invokeStatic + MethodHandle()Consumer
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_LL
linkCallSite target => (Object,int)int : invoke002_LLI_I=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:L,a2:I)=>{
    t3:L=BoundMethodHandle$Species_LL.argL1(a0:L);
    t4:L=BoundMethodHandle$Species_LL.argL0(a0:L);
    t5:I=MethodHandle.invokeBasic(t4:L,a1:L,a2:I,t3:L);t5:I}
& BMH=[
  0: MethodHandle = {(Object,int,Object[])int : DMH.invokeStaticInit001_LLIL_I=Lambda(a0:L,a1:L,a2:I,a3:L)=>{
        t4:L=DirectMethodHandle.internalMemberNameEnsureInit(a0:L);
        t5:I=MethodHandle.linkToStatic(a1:L,a2:I,a3:L,t4:L);t5:I}
    & DMH.MN=java.lang.runtime.SwitchBootstraps.doTypeSwitch(Object,int,Object[])int/invokeStatic
  }
  1: ( [Ljava.lang.Object;@6d06d69c )
]
linkCallSite linkage => java.lang.invoke.LambdaForm$MH/0x0000000801003800.linkToTargetMethod000_LIL_I(Object,int,Object)int/invokeStatic + MethodHandle(Object,int)int
String Array

======== CallSite: java.base/java.lang.runtime.SwitchBootstraps.typeSwitch(SwitchBootstraps.java:128)
BSM = java.base/java.lang.runtime.SwitchBootstraps.typeSwitch(SwitchBootstraps.java:128)
target class = java.lang.invoke.BoundMethodHandle$Species_L
target = ()Consumer : invoke=Lambda(a0:L/SpeciesData[L => Species_L])=>{
    t1:L=Species_L.argL0(a0:L);t1:L}
& BMH=[