Is there any way to check password hash sync status in Java code?

I'm afraid there's no SDK to get the status of password hash sync. Only Get-ADSyncAADCompanyFeature can help you.

You could try to create a powershell script and then invoke the powershell script from java.

Import-Module ADSync
$connectors = Get-ADSyncConnector
$aadConnectors = $connectors | Where-Object {$_.SubType -eq "Windows Azure Active Directory (Microsoft)"}
$adConnectors = $connectors | Where-Object {$_.ConnectorTypeName -eq "AD"}
if ($aadConnectors -ne $null -and $adConnectors -ne $null)
{
    if ($aadConnectors.Count -eq 1)
    {
        $features = Get-ADSyncAADCompanyFeature
        Write-Host
        Write-Host "Password sync feature enabled in your Azure AD directory: "  $features.PasswordHashSync
        foreach ($adConnector in $adConnectors)
        {
            Write-Host
            Write-Host "Password sync channel status BEGIN ------------------------------------------------------- "
            Write-Host
            Get-ADSyncAADPasswordSyncConfiguration -SourceConnector $adConnector.Name
            Write-Host
            $pingEvents =
                Get-EventLog -LogName "Application" -Source "Directory Synchronization" -InstanceId 654  -After (Get-Date).AddHours(-3) |
                    Where-Object { $_.Message.ToUpperInvariant().Contains($adConnector.Identifier.ToString("D").ToUpperInvariant()) } |
                    Sort-Object { $_.Time } -Descending
            if ($pingEvents -ne $null)
            {
                Write-Host "Latest heart beat event (within last 3 hours). Time " $pingEvents[0].TimeWritten
            }
            else
            {
                Write-Warning "No ping event found within last 3 hours."
            }
            Write-Host
            Write-Host "Password sync channel status END ------------------------------------------------------- "
            Write-Host
        }
    }
    else
    {
        Write-Warning "More than one Azure AD Connectors found. Please update the script to use the appropriate Connector."
    }
}
Write-Host
if ($aadConnectors -eq $null)
{
    Write-Warning "No Azure AD Connector was found."
}
if ($adConnectors -eq $null)
{
    Write-Warning "No AD DS Connector was found."
}
Write-Host

For more details, see here.