NSIS- String Concatenation & Cheking Java Versions

1.  How to do String concatenation ?

outfile test.exe
requestexecutionlevel user
page instfiles
section
;init strings
strcpy $1 "Hello: "
strcpy $2 foo
strcpy $3 bar
strcpy $4 baz

strcpy $1 "$1$2"
strcpy $1 "$1$3"
strcpy $1 "$1$4"
DetailPrint $1 ;prints "Hello: foobarbaz"
sectionend

2.  Checking Installed java Families ?
 

ReadRegStr $9 HKLM "SOFTWARE\JavaSoft\Java Runtime Environment" "CurrentVersion"

MessageBox MB_OK "Found System JRE Version- $9"

${If} $9 == ''

  MessageBox MB_OK " JRE is not available in your system. Please install Java6 or Java7 and try to install IPCOM again.$\n This installation process will be Aborted."

  RMDir /r $INSTDIR

  Quit

${EndIf}

ReadRegStr $6 HKLM "SOFTWARE\JavaSoft\Java Runtime Environment" "Java6FamilyVersion"

ReadRegStr $7 HKLM "SOFTWARE\JavaSoft\Java Runtime Environment" "Java7FamilyVersion"

ReadRegStr $8 HKLM "SOFTWARE\JavaSoft\Java Runtime Environment" "Java8FamilyVersion"

${If} $6 != ''

StrCpy $1 $6

MessageBox MB_OK " Installed JRE Versions -$\n $1"

${EndIf}

${If} $7 != ''

StrCpy $1 "$1$\n$7"

MessageBox MB_OK " Installed JRE Versions - $\n $1"

${EndIf}

${If} $8 != ''

StrCpy $1 "$1$\n$8"

MessageBox MB_OK " Installed JRE Versions - $\n $1"

${EndIf}