java - What is dereferencing possible null pointer? -

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i making program sftp in netbeans.

some part of 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);        } {             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 resolve these warnings??? can disconnect session , channel???

sessiontarget = jsch.getsession(backupuser, backuphost, backupport); here in line, getsession() method can throw exception, , hence variables sessiontarget , channeltarget null, , in block, accessing variables, may cause null pointer exception.

to avoid this, in block check null before accessing variable.

finally {   if (channeltarget != null) {        channeltarget.exit();             channeltarget.disconnect();     }   if (sessiontarget != null ) {        sessiontarget.disconnect();     } }

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