public class StrConcat {
    static String hello = "Hello";
    static String world = "World";
    public static void main(String args[]) {
        System.out.println(hello + world);
        System.out.println(hello + "World");
        System.out.println(hello + args.length);
    }
}

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

$ java -Djava.lang.invoke.MethodHandle.TRACE_CALLSITE=true -cp . StrConcat > ~/Documents/str-concat.txt
linkCallSite StrConcat.main(StrConcat.java:5) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String,String)String/BSA1=


linkMethod java.lang.invoke.MethodHandle.invokeExact(Lookup,String,MethodType,String,Object[])CallSite/5
linkMethod => java.lang.invoke.Invokers$Holder.invokeExact_MT(Object,Object,Object,Object,Object,Object,Object)Object/invokeStatic + (Lookup,String,MethodType,String,Object[])CallSite
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_L
linkCallSite target => (String,String)String : BMH.reinvoke000_LLL_L=Lambda(a0:L/SpeciesData[L => Species_L],a1:L,a2:L)=>{
    t3:L=Species_L.argL0(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L,a2:L);t4:L}
& BMH=[
  0: MethodHandle = {(Object,Object)String : DMH.invokeStatic000_LLL_L=Lambda(a0:L,a1:L,a2:L)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
  }
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,Object,Object)Object/invokeStatic + MethodHandle(String,String)String
HelloWorld
linkCallSite StrConcat.main(StrConcat.java:6) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String)String/BSA1=
World
linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_LL
linkCallSite target => (String)String : invoke000_LL_L=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:L)=>{
    t2:L=BoundMethodHandle$Species_LL.argL1(a0:L);
    t3:L=BoundMethodHandle$Species_LL.argL0(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L,t2:L);t4:L}
& BMH=[
  0: MethodHandle = {(Object,Object)String : DMH.invokeStatic000_LLL_L=Lambda(a0:L,a1:L,a2:L)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:L,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.simpleConcat(Object,Object)String/invokeStatic
  }
  1: ( World )
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,Object)Object/invokeStatic + MethodHandle(String)String
HelloWorld
linkCallSite StrConcat.main(StrConcat.java:7) java.lang.invoke.StringConcatFactory.makeConcatWithConstants(Lookup,String,MethodType,String,Object[])CallSite/invokeStatic makeConcatWithConstants(String,int)String/BSA1=


linkCallSite target class => java.lang.invoke.BoundMethodHandle$Species_LLLLL
linkCallSite target => (String,int)String : invoke014_LLI_L=Lambda(a0:L/SpeciesData[LLLLL => BoundMethodHandle$Species_LLLLL],a1:L,a2:I)=>{
    t3:L=BoundMethodHandle$Species_LLLLL.argL4(a0:L);
    t4:L=MethodHandle.invokeBasic(t3:L,a1:L);
    t5:L=BoundMethodHandle$Species_LLLLL.argL3(a0:L);
    t6:J=MethodHandle.invokeBasic(t5:L,t4:L,a2:I);
    t7:L=BoundMethodHandle$Species_LLLLL.argL2(a0:L);
    t8:L=MethodHandle.invokeBasic(t7:L,t6:J);
    t9:L=BoundMethodHandle$Species_LLLLL.argL1(a0:L);
    t10:J=MethodHandle.invokeBasic(t9:L,t6:J,t8:L,t4:L,a2:I);
    t11:L=BoundMethodHandle$Species_LLLLL.argL0(a0:L);
    t12:L=MethodHandle.invokeBasic(t11:L,t8:L,t10:J);t12:L}
& BMH=[
  0: MethodHandle = {(byte[],long)String : DMH.invokeStatic001_LLJ_L=Lambda(a0:L,a1:L,a2:J)=>{
        t3:L=DirectMethodHandle.internalMemberName(a0:L);
        t4:L=MethodHandle.linkToStatic(a1:L,a2:J,t3:L);t4:L}
    & DMH.MN=java.lang.StringConcatHelper.newString(byte[],long)String/invokeStatic
  }
  1: MethodHandle = {(long,byte[],String,int)long : invoke007_LJLLI_J=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:J,a2:L,a3:L,a4:I)=>{
        t5:L=BoundMethodHandle$Species_LL.argL1(a0:L);
        t6:J=MethodHandle.invokeBasic(t5:L,a1:J,a2:L,a4:I);
        t7:L=BoundMethodHandle$Species_LL.argL0(a0:L);
        t8:J=MethodHandle.invokeBasic(t7:L,t6:J,a2:L,a3:L);t8:J}
    & BMH=[
      0: MethodHandle = {(long,byte[],String)long : invoke004_LJLL_J=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:J,a2:L,a3:L)=>{
            t4:L=BoundMethodHandle$Species_LL.argL1(a0:L);
            t5:L=BoundMethodHandle$Species_LL.argL0(a0:L);
            t6:J=MethodHandle.invokeBasic(t5:L,a1:J,a2:L,a3:L,t4:L);t6:J}
        & BMH=[
          0: MethodHandle = {(long,byte[],String,String)long : DMH.invokeStatic002_LJLLL_J=Lambda(a0:L,a1:J,a2:L,a3:L,a4:L)=>{
                t5:L=DirectMethodHandle.internalMemberName(a0:L);
                t6:J=MethodHandle.linkToStatic(a1:J,a2:L,a3:L,a4:L,t5:L);t6:J}
            & DMH.MN=java.lang.StringConcatHelper.prepend(long,byte[],String,String)long/invokeStatic
          }
          1: ( null )
        ]
      }
      1: MethodHandle = {(long,byte[],int)long : invoke006_LJLI_J=Lambda(a0:L/SpeciesData[LL => BoundMethodHandle$Species_LL],a1:J,a2:L,a3:I)=>{
            t4:L=BoundMethodHandle$Species_LL.argL1(a0:L);
            t5:L=BoundMethodHandle$Species_LL.argL0(a0:L);
            t6:J=MethodHandle.invokeBasic(t5:L,a1:J,a2:L,a3:I,t4:L);t6:J}
        & BMH=[
          0: MethodHandle = {(long,byte[],int,String)long : DMH.invokeStatic003_LJLIL_J=Lambda(a0:L,a1:J,a2:L,a3:I,a4:L)=>{
                t5:L=DirectMethodHandle.internalMemberName(a0:L);
                t6:J=MethodHandle.linkToStatic(a1:J,a2:L,a3:I,a4:L,t5:L);t6:J}
            & DMH.MN=java.lang.StringConcatHelper.prepend(long,byte[],int,String)long/invokeStatic
          }
          1: ( null )
        ]
      }
    ]
  }
  2: MethodHandle = {(long)byte[] : DMH.invokeStatic004_LJ_L=Lambda(a0:L,a1:J)=>{
        t2:L=DirectMethodHandle.internalMemberName(a0:L);
        t3:L=MethodHandle.linkToStatic(a1:J,t2:L);t3:L}
    & DMH.MN=java.lang.StringConcatHelper.newArray(long)byte[]/invokeStatic
  }
  3: MethodHandle = {(String,int)long : invoke012_LLI_J=Lambda(a0:L/SpeciesData[LLJ => BoundMethodHandle$Species_LLJ],a1:L,a2:I)=>{
        t3:J=BoundMethodHandle$Species_LLJ.argJ2(a0:L);
        t4:L=BoundMethodHandle$Species_LLJ.argL1(a0:L);
        t5:J=MethodHandle.invokeBasic(t4:L,t3:J,a2:I);
        t6:L=BoundMethodHandle$Species_LLJ.argL0(a0:L);
        t7:J=MethodHandle.invokeBasic(t6:L,t5:J,a1:L);t7:J}
    & BMH=[
      0: MethodHandle = {(long,String)long : DMH.invokeStatic005_LJL_J=Lambda(a0:L,a1:J,a2:L)=>{
            t3:L=DirectMethodHandle.internalMemberName(a0:L);
            t4:J=MethodHandle.linkToStatic(a1:J,a2:L,t3:L);t4:J}
        & DMH.MN=java.lang.StringConcatHelper.mix(long,String)long/invokeStatic
      }
      1: MethodHandle = {(long,int)long : BMH.reinvoke001_LJI_J=Lambda(a0:L/SpeciesData[L => Species_L],a1:J,a2:I)=>{
            t3:L=Species_L.argL0(a0:L);
            t4:J=MethodHandle.invokeBasic(t3:L,a1:J,a2:I);t4:J}
        & BMH=[
          0: MethodHandle = {(long,int)long : DMH.invokeStatic006_LJI_J=Lambda(a0:L,a1:J,a2:I)=>{
                t3:L=DirectMethodHandle.internalMemberName(a0:L);
                t4:J=MethodHandle.linkToStatic(a1:J,a2:I,t3:L);t4:J}
            & DMH.MN=java.lang.StringConcatHelper.mix(long,int)long/invokeStatic
          }
        ]
      }
      2: ( 0 )
    ]
  }
  4: MethodHandle = {(Object)String : DMH.invokeStatic007_LL_L=Lambda(a0:L,a1:L)=>{
        t2:L=DirectMethodHandle.internalMemberName(a0:L);
        t3:L=MethodHandle.linkToStatic(a1:L,t2:L);t3:L}
    & DMH.MN=java.lang.StringConcatHelper.stringOf(Object)String/invokeStatic
  }
]
linkCallSite linkage => java.lang.invoke.Invokers$Holder.linkToTargetMethod(Object,int,Object)Object/invokeStatic + MethodHandle(String,int)String
Hello0