Attempting to find java.exe, on a Windows machine, in a way that's semi-reliable across Java versions, operating system versions, 32 vs 64-bit and whatever else can be thrown at us.

Find-JavaExe.ps1

function Find-JavaExe {
    <#

    .SYNOPSIS

    Locates java.exe on the current system via common conventions.


    .DESCRIPTION

    Searches $env:JAVAHOME, path variables, and the registry (http://stackoverflow.com/a/5415532/211747)


    .EXAMPLE

    Find java.exe, or throw an error if it can't be found.

    $JavaExePath = Find-JavaExe


    .EXAMPLE

    Find java.exe, or return null if it can't be found.

    $JavaExePathOrNull = Find-JavaExe -ErrorAction SilentlyContinue

    #>
    [CmdletBinding()]
    param ()

    $JavaExeSuffix = 'bin\java.exe'

    if ($env:JAVAHOME -eq $null) {
        Write-Debug "`$env:JAVAHOME doesn't exist, going to look elsewhere"
    }
    else {
        $JavaHomeBasedPath = Join-Path $env:JAVAHOME $JavaExeSuffix
        Write-Debug "Testing for $JavaHomeBasedPath, based on `$env:JAVAHOME"
        if (Test-Path $JavaHomeBasedPath) {
            Write-Debug "Found $JavaExePath"
            return $JavaExePath
        }
    }

    $FileSearchPaths = $env:Path.Split(';')
    $JavaExePath = $FileSearchPaths |
        where {
            $PotentialPath = Join-Path $_ $JavaExeSuffix
            Write-Debug "Testing for $PotentialPath, based on path variable $_"
            if (Test-Path $PotentialPath) { $PotentialPath }
        } |
        select -First 1

    if ($JavaExePath -ne $null) {
        Write-Debug "Found $JavaExePath"
        return $JavaExePath
    }

    $RegistrySearchPaths = @('HKLM:\SOFTWARE\JavaSoft\Java Runtime Environment\', 'HKLM:\SOFTWARE\Wow6432Node\JavaSoft\Java Runtime Environment\')
    $JavaExePath = $RegistrySearchPaths |
        where { Test-Path $_ } |
        % {
            $CurrentVersion = (Get-ItemProperty $_).CurrentVersion
            Write-Debug "Current Java version is $CurrentVersion, based on $($_)"
            $VersionKey = Join-Path $_ $CurrentVersion
            $JavaHomeBasedPath = Join-Path (Get-ItemProperty $VersionKey).JavaHome $JavaExeSuffix
            Write-Debug "Testing for $JavaHomeBasedPath, based on $VersionKey\JavaHome"
            if (Test-Path $JavaHomeBasedPath) { $JavaHomeBasedPath }
        } |
        select -First 1

    if ($JavaExePath -ne $null) {
        Write-Debug "Found $JavaExePath"
        return $JavaExePath
    }

    Write-Error "We couldn't resolve java.exe. We looked for `$env:JAVAHOME, then checked environment paths and the registry. The full set of search paths were written to the debug output stream."
}

Also, here's my implementation. It avoids the registry and any other config, which are sometimes unreliable and just scans the Program directory for any Java directory that still has a \bin directory (Java updates sometimes remove old versions by deleting the \bin dir)

https://github.com/Orbixx/findjava/blob/master/findJava.ps1