java - Private variable cannot reference to another method in the same class -


im new java , today have problem code when trying actionlistener java class here:

public class exam{     private void createform(){         ...         jbutton jbtn = new jbutton("ok");         jbtn.addactionlistener((actionlistener) this);         ...     }     public static void main(string[] args){         exam ex = new exam();         ex.createform();     }     public void actionperformed(actionevent ae){         //ide show no variable name "jbtn"         if (ae.getsource() == jbtn){             ...         }     } }

your jbtn variable declared within createform method. java uses called "scoping rules" make sure don't accidentally use variables don't mean to. declaring jbtn in createform, telling java compiler want use in method, , else. called "local" variable (as in, local method).

you want use "member variable" (it member of class). declared inside class, outside of method. in case, looks this:

public class exam{     jbutton jbtn;      private void createform(){         ...         jbtn = new jbutton("ok");         jbtn.addactionlistener((actionlistener) this);         ...     }

the declaration of variable @ class level, , in createform being referenced in same way in actionperformed.

this basic concept in java, might want take @ java tutorials go on ground. official tutorial place start.


Comments

Post a Comment

Popular posts from this blog

c++ - Difference between pre and post decrement in recursive function argument -

i have following sample code used pre-decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(--c); cout << c << endl; return; } } this function give output input 4 : dp3 dp2 dp1 dp0 0 1 2 3 but when use post decrement void function(int c) { if(c == 0) { return; } else { cout << "dp" << c << endl; function(c--); cout << c << endl; return; } } output goes in infinite loop dp4 can explain me in detail why happens ? this happens because function(c--) called same value of c , when finishes c decremented. recursively called, hence called same value no chance of return , hit stack overflow error. assume this, int x = 1, y = 0; y = x++ result y == 1 , x == 2. if y = ++x , bot x , y 2.
Read more

php - Nothing but 'run(); ' when browsing to my local project, how do I fix this? -

i added new project. made mistake in projectname.conf file in sites-available apache2, led me reinstalling apache2. after reinstalling , re-enabling projects on every page of every project .. <body> run(); </body> .. i've run composer update, restarted service, restarted pc, checked config files, tried disabling new project. there nothing in error log, , access.log: 127.0.0.1 - - [15/may/2015:01:40:47 +0200] "get / http/1.1" 304 181 "-" "mozilla/5.0 (x11; ubuntu; linux x86_64; rv:38.0) gecko/20100101 firefox/38.0" maybe i'm forgetting apache2 reinstall? don't think did different last time installed it. looks haven't setup php correctly. take @ this great guide , maybe you're forgetting link php config apache2.
Read more

php - How can I echo out this array? -

i don't know how go grabbing data in variable , put foreach loop. class tree{ private $info = array( array('name'=>'jim','state'=>'nu','company'=>'nu','phone'=>array('cell'=>'5615111111','office'=>'5611111111'),'email'=>array('primary'=>'exs@example.com','ex@there.com')), array('name'=>'joe smith','city'=>'phoenix','phone'=>'4805551111','email'=>'jsmith@some_email.com'), array('name'=>'john doe','city'=>'chandler','company'=>'doe co.','email'=>array('jdoe@gmail.com','personal'=>'email@email.com'),'phone'=>'6025550002') ); } if you're inside of class, can access private variable using $this->variablename . example, i...
Read more