java - Null pointer exception on method -


this question has answer here:

this first every java project.all going , program compiled. got 3d looking object on screen. when use moveto(int x,int y) method null pointer exception. i've looked , it's huge issue lot of people. still can't grasp concept of , of fixes worked other people don't seem fit program. have tried using if statements check null , stuff can't syntax right or something. example base ellipse , ellipse class has moveto(x,y) method.but when call on using base.moveto(x,y) im getting error. can help? cylinder1.moveto(8, 8); exception occurred. java.lang.nullpointerexception @ cylinder3d.moveto(cylinder3d.java:57) ment stack trace? here code moveto method in rectangle class. public void moveto(int x, int y) { xposition = x; yposition = y; makevisible(); draw(); }

public class cylinder3d {         private int diameter;     private int height;     private ellipse top;     private ellipse base;     private rectangle wall;     int xposition;     int yposition;       public cylinder3d(int diameter, int height)     {         int x = 0;         int y = 0;         ellipse top = new ellipse();         int xdiameter=diameter;         int ydiameter=diameter/2;         int xposition = 0;         int yposition = 0;         top.setstate(xdiameter,ydiameter,xposition,yposition,"black");          ellipse base = new ellipse();         int ypositionbase = yposition + height;         base.setstate(xdiameter,ydiameter,xposition,ypositionbase,"black");           rectangle wall = new rectangle();         int xsidelenght = diameter;         int ysidelenght = height;         int ypositionwall = yposition + (diameter/4);         wall.setstate(xsidelenght,ysidelenght,xposition,ypositionwall,"black");         //....      }        public void moveto(int x, int y)     {         wall.moveto(x,y); //here error.         base.moveto(x,y);         top.moveto(x,y);     } }

your constructor not touch of member variables top, base , wall, because local variables declared in constructor shadow member variables want initialise.

thus, stay null, , trying call member functions on them in moveto throws.


Comments

Post a Comment

Popular posts from this blog

apache - Remove .php and add trailing slash in url using htaccess not loading css -

i have add following code htaccess file removing .php extension , add trailing slash urls. worked fine reduced page loading speed , css code not loading @ all. pages ugly. please help rewriteengine on rewritebase / ## hide .php extension snippet # externally redirect /dir/foo.php /dir/foo rewritecond %{the_request} ^[a-z]{3,}\s([^.]+)\.php [nc] rewriterule ^ %1/ [r,l] # add trailing slash rewritecond %{request_filename} !-f rewritecond %{request_uri} !/$ rewriterule . %{request_uri}/ [l,r=301] # internally forward /dir/foo /dir/foo.php rewritecond %{request_filename} !-d rewritecond %{request_filename}.php -f rewriterule ^(.*?)/?$ $1.php [l] we can rewrite urls using .htaccess files. before writing in .htaccess files need verify kind of server using. can check server adding a <?php phpinfo(); ?> in php page. ensure mod_rewrite module enabled in apache server. can identified checking phpinfo included page. common methods used url rewriting follows ...
Read more

inno setup - TLabel or TNewStaticText - change .Font.Style on Focus like Cursor changes with .Cursor -

is possible change .font.style on focus tlabel or tnewstatictext happens cursor when use .cursor ? there no built-in support track mouse hovering in inno setup @ time. however, intercepting window procedure of controls can track yourself. following example need innocallback library: [setup] appname=my program appversion=1.5 defaultdirname={pf}\my program outputdir=userdocs:inno setup examples output [files] source: "innocallback.dll"; destdir: "{tmp}"; flags: dontcopy [code] #ifdef unicode #define aw "w" #else #define aw "a" #endif const gwl_wndproc = -4; wm_mousemove = $0200; type wparam = uint_ptr; lparam = longint; lresult = longint; twindowproc = function(hwnd: hwnd; umsg: uint; wparam: wparam; lparam: lparam): lresult; function setcapture(hwnd: hwnd): hwnd; external 'setcapture@user32.dll stdcall'; function releasecapture: bool; external 'releasecapture@user32.dll stdcall'; func...
Read more