NullPointerException in java (javafx) -

this main.java

public class main extends application {      radiobutton chksort;     radiobutton chkorder;      public static void main(string[] args) {          launch(args);     }      public static comparator<student> studentidcomparator = new comparator<student>() {           public int compare(student std1, student std2) {           string id1 = std1.getid();          string id2 = std2.getid();          return id1.comparetoignorecase(id2);          }          };       public static comparator<student> studentnamecomparator = new comparator<student>() {           public int compare(student std1, student std2) {           string name1 = std1.getname();          string name2 = std2.getname();          return name1.comparetoignorecase(name2);          }          };      public static comparator<student> studentlastnamecomparator = new comparator<student>() {           public int compare(student std1, student std2) {           string last1 = std1.getlastname();          string last2 = std2.getlastname();          //ascending order           return last1.comparetoignorecase(last2);          }          //return fruitname2.compareto(fruitname1); //descending order           };      public static comparator<student> studentgpacomparator = new comparator<student>() {           public int compare(student std1, student std2) {           string gpa1 = std1.getgpa();          string gpa2 = std2.getgpa();           return gpa1.compareto(gpa2);          }         };      @override        public void start(stage primarystage) throws exception{         primarystage.settitle("student sorting");         splitpane splitpane = new splitpane();         gridpane grid1 = new gridpane();         gridpane grid2 = new gridpane();          grid1.setalignment(pos.top_left);         grid1.setvgap(10);         grid1.sethgap(10);         grid1.setpadding(new insets(25,25,25,25));         grid2.setpadding(new insets(25,25,25,25));         scene scene = new scene(splitpane, 700, 500);         primarystage.setscene(scene);          text title = new text("student sorting");         title.setfont(font.font("comic sans ms", fontweight.bold, 20));          text sortby = new text("sort :");         sortby.setfont(font.font("calibri", fontweight.bold, 14));          final togglegroup toselect = new togglegroup();         final togglegroup toorder = new togglegroup();          radiobutton idbtn = new radiobutton("id");         idbtn.settogglegroup(toselect);          radiobutton namebtn = new radiobutton("name");         namebtn.settogglegroup(toselect);          radiobutton lastnamebtn = new radiobutton("last name");         lastnamebtn.settogglegroup(toselect);          radiobutton gpabtn = new radiobutton("gpa");         gpabtn.settogglegroup(toselect);          text order = new text("order :");         order.setfont(font.font("calibri", fontweight.bold, 14));          radiobutton ascbtn = new radiobutton("ascending");         ascbtn.settogglegroup(toorder);         ascbtn.setuserdata("asc");          radiobutton desbtn = new radiobutton("descending");         desbtn.settogglegroup(toorder);         desbtn.setuserdata("des");          button start = new button("sort");         start.setprefsize(170, 20);          final textarea text = new textarea();         text.setminsize(500, 400);          grid1.add(title, 0, 0);         grid1.add(sortby, 0, 2);         grid1.add(idbtn, 0, 3);         grid1.add(namebtn, 0, 4);         grid1.add(lastnamebtn, 0, 5);         grid1.add(gpabtn, 0, 6);         grid1.add(order, 0, 8);         grid1.add(ascbtn, 0, 9);         grid1.add(desbtn, 0, 10);         grid1.add(start, 0, 13);          grid2.add(text, 2, 2);         splitpane.getitems().addall(grid1, grid2);         splitpane.setdividerpositions(0.3);          toselect.selectedtoggleproperty().addlistener(new changelistener<toggle> (){             @override             public void changed(observablevalue<? extends toggle> value,                     toggle t1, toggle t2) {                 chksort = (radiobutton) t2.gettogglegroup().getselectedtoggle();             }                    });          toorder.selectedtoggleproperty().addlistener(new changelistener<toggle> (){             @override             public void changed(observablevalue<? extends toggle> value,                     toggle t1, toggle t2) {                 chkorder = (radiobutton) t2.gettogglegroup().getselectedtoggle();                }          });          start.setonaction(new eventhandler<actionevent>(){              @override             public void handle(actionevent arg0) {                 string temp =text.gettext().tostring();                 string[] splitline = temp.split("\n");                 student[] stddata = new student[splitline.length];                 for(int i=0; i<splitline.length; i++){                     string[] stddatastr = splitline[i].split(" ");                     if(stddatastr[i].length() <4 || stddatastr[i].equals(null)){                         text.settext("invalid input");                         break;                     }                     else {                          stddata[i].setid(stddatastr[0]);                         stddata[i].setname(stddatastr[1]);                         stddata[i].setlastname(stddatastr[2]);                         stddata[i].setgpa(stddatastr[3]);                      }                 }                     if(chksort.gettext().tostring().equals("id")){                     if(chkorder.gettext().tostring().equals("ascending")){                         student.sort(stddata,studentidcomparator , true);                     }                     else{                         student.sort(stddata, studentidcomparator, false);                     }                 }                 else if(chksort.gettext().tostring().equals("name")){                     if(chkorder.gettext().tostring().equals("ascending")){                         student.sort(stddata, studentnamecomparator, true);                     }                     else{                         student.sort(stddata, studentnamecomparator, false);                     }                 }                 else if(chksort.gettext().tostring().equals("last name")){                     if(chkorder.gettext().tostring().equals("ascending")){                         student.sort(stddata, studentlastnamecomparator, true);                     }                     else{                         student.sort(stddata, studentlastnamecomparator, false);                     }                 }                 else if(chksort.gettext().tostring().equals("gpa")){                     if(chkorder.gettext().tostring().equals("ascending")){                         student.sort(stddata, studentgpacomparator, true);                     }                     else{                         student.sort(stddata, studentgpacomparator, false);                     }                 }                  for(int i=0 ; i<stddata.length; i++){                     text.settext(stddata[i].getid()+" "+stddata[i].getname()+" "+stddata[i].getlastname()+" "+stddata[i].getgpa());                 }             }                });          primarystage.show();             }    } 

this student.java

    public class student {     private string stdid;     private string stdname;     private string stdlastname;     private string stdgpa;      public student(string id, string name, string lastname, string gpa) {           super();           this.stdid = id;          this.stdname = name;          this.stdlastname = lastname;          this.stdgpa = gpa;         }       public string getid() {return stdid;}      public void setid(string id) { this.stdid =id; }      public string getname() {return stdname;}      public void setname(string name) { this.stdname= name; }     public string getlastname() {return stdlastname;}      public void setlastname(string lastname) { this.stdlastname = lastname; }     public string getgpa() {return stdgpa;}      public void setgpa(string gpa) { this.stdgpa = gpa; }      public static void sort(student[] std, comparator<student> c, boolean asc){           student tmp;          (int i=0; i<std.length-1;i++){              for(int j=i+1;j<std.length;j++)                  if((c.compare(std[i],std[j]) >0 && asc==true) ||(c.compare(std[i],std[j]) <0 && asc==false)) {                      tmp = std[i]; std[i] = std[j]; std[j] = tmp;                  }           }      }  } 

this nullpointerexception appear

else { stddata[i].setid(stddatastr[0]); stddata[i].setname(stddatastr[1]); stddata[i].setlastname(stddatastr[2]); stddata[i].setgpa(stddatastr[3]);    } 

this java src when try run nullpointerexception when try setid, setname, setlastname , setgpa should do?

thanks all

you're initializing stddata array of students don't create new student in each entry , try access student in entry doesn't exist.

what should is, after lines:

student[] stddata = new student[splitline.length];     for(int i=0; i<splitline.length; i++){ 

add initialization:

stddata[i] = new student(); 

and continue - later in code you'll able stuff like:

stddata[i].setid(stddatastr[0]); 

tip:
when post question - try post relevant code, add stacktrace , mark line triggers compilation/run-time error.