What is dereferencing possible null pointer?

Question

I am making a program for SFTP in NetBeans.

Some part of My code:

com.jcraft.jsch.Session sessionTarget = null;
com.jcraft.jsch.ChannelSftp channelTarget = null;
try {
       sessionTarget = jsch.getSession(backupUser, backupHost, backupPort);
       sessionTarget.setPassword(backupPassword);
       sessionTarget.setConfig("StrictHostKeyChecking", "no");
       sessionTarget.connect();
       channelTarget = (ChannelSftp) sessionTarget.openChannel("sftp");
       channelTarget.connect();

       System.out.println("Target Channel Connected");
       } catch (JSchException e) {
            System.out.println("Error Occured ======== Connection not estabilished");
            log.error("Error Occured ======== Connection not estabilished", e);
       } finally {
            channelTarget.exit();     // Warning : dereferencing possible null pointer
            channelTarget.disconnect();  // Warning : dereferencing possible null pointer
            sessionTarget.disconnect();  // Warning : dereferencing possible null pointer
        }

I'm getting warning dereferencing possible null pointer, how can I resolve these warnings??? Where I can disconnect my Session and Channel???

Abimaran Kugathasan · Accepted Answer · 2022-10-14T03:32:20.313

sessionTarget = jsch.getSession(backupUser, backupHost, backupPort); Here in this line, getSession() method can throw an Exception, and hence the variables sessionTarget and channelTarget will be null, and in the finally block, you are accessing those variables, which may cause null pointer exception.

To avoid this, in the finally block check for null before accessing the variable.

finally {
  if (channelTarget != null) {
       channelTarget.exit();     
       channelTarget.disconnect();  
  }
  if (sessionTarget != null ) {
       sessionTarget.disconnect();  
  }
}

score 1 · Answer 2 · answered Feb 06 '14 at 07:09

1

That means: what if your channelTarget and sessionTarget are null in your finally block? Check them for null to avoid the warning.

answered Feb 06 '14 at 07:09

sadhu

1,429
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score -2 · Answer 3 · answered Feb 06 '14 at 07:11

-2

I think netbeans is just trying to warn you that these may be null which may not be necasarilly true. You can choose to disable the warnings though. Just place your cursor on the warning press ALT+ENTER and choose from the choices even to disable the warnings.

answered Feb 06 '14 at 07:11

Stanley Mungai

4,044
30
100
168

2

As a general rule, you don't want to ignore/disable a warning unless you know for a fact that everything will be okay. Disabling this kind of warning does *not* fall under that category; if you might be dereferencing null, figuring out at compile time is *much* better than having to debug a NullPointerException. – Dennis Meng Feb 06 '14 at 07:13

What is dereferencing possible null pointer?

3 Answers3