Unable to resolve java.lang.nullpointerexception

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Exception in thread "main" java.lang.NullPointerException
	at EnrollmentMain.main(EnrollmentMain.java:211)

Getting this exception while running following program I don't understand what is this could you explain me how? i've search like 1-2hours to resolve this buy i couldn't understand this exception keeps popping up pardon me because I'm new thanks for your understanding and consideration.

What I have tried:

Here's the line 211:

for(int i=0; i<=count;i++){
                   System.out.println(students[i].getID());
               }

Posted 24-Sep-18 22:10pm

Member 13996630

Updated 24-Sep-18 22:56pm

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CPallini · Answer 1 · 2018-09-24T22:16:00

Solution 1

If count is the length of the students array then the upper limit of the loop is wrong: Change from

Quote:
for(int i=0; i<=count;i++){

to

Java

for(int i=0; i<count;i++){

Posted 24-Sep-18 22:16pm

CPallini

Comments

Member 13996630 25-Sep-18 4:26am

The same problem sir "Exception in thread "main" java.lang.NullPointerException"

CPallini 25-Sep-18 4:53am

Then you should show us more code.

Member 13996630 25-Sep-18 5:01am

mport java.io.*;
import java.util.Scanner;

public class EnrollmentMain {
public static void main(String[] args) {

Subjects[] subjects = new Subjects[100];
System.out.println(java.util.Arrays.toString(subjects));
Students[] students = new Students[100];
System.out.println(java.util.Arrays.toString(students));
Schedules[] schedules = new Schedules[100];
System.out.println(java.util.Arrays.toString(schedules));

char exit ='y';

String input;

int count=0;
int count2=0;
int count3=0;

Scanner scan = new Scanner( System.in );
boolean shouldBreak = false;
while(exit!='n') {
try{

InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);

String subid;
String code;
String lecdesc;
String lab;
String units1;
String units2;
String id;
String name;
String address;
String course;
String yr;
String sy;
String sem;
String time1;
String time2;
String day1;
String day2;
String rooms1;
String rooms2;
String sec;

int choice;
while(!shouldBreak){
System.out.println("\nMenu");
System.out.println("[1] Enter Subjects");
System.out.println("[2] Enter Students");
System.out.println("[3] Enter Schedules");

System.out.print("Choice: ");

choice=Integer.parseInt(br.readLine());

switch(choice){
case 0:
shouldBreak = true;
break;
case 1:
subjects[count]= new Subjects();
System.out.print("Enter Subject Code: ");
code = br.readLine();
subjects[count].setCode(code);

System.out.print("Enter Subject Id: ");
subid = br.readLine();
subjects[count].setSubid(subid);

System.out.print("Enter Subject Description(Lec): ");
lecdesc = br.readLine();
subjects[count].setLecdesc(lecdesc);

System.out.print("Enter Subject Description(Lab): ");
lab = br.readLine();
subjects[count].setLab(lab);

System.out.print("Enter Subject Lecture Units: ");
units1 = br.readLine();
subjects[count].setUnits1(units1);

System.out.print("Enter Subject Laboratory Units: ");
units2 = br.readLine();
subjects[count].setUnits2(units1);

count++;

CPallini 25-Sep-18 5:09am

Add the code to your original question, please.

Member 13996630 25-Sep-18 5:02am

System.out.println("\nSubject Information");
System.out.println("Code:" + subjects[count].getCode());
System.out.println("Subid:" + subjects[count].getSubid());
System.out.println("Subject Description(Lec):" + subjects[count].getLecdesc());
System.out.println("Subject Description(Lab):" + subjects[count].getLab());
System.out.println("Lecture Units:" + subjects[count].getUnits1());
System.out.println("Laboratory Units:" + subjects[count].getUnits2());
break;

case 2:
students[count2]= new Students();
System.out.print("\nEnter Student ID: ");
id= br.readLine();
students[count2].setID(id);

System.out.print("Enter Student Name: ");
name= br.readLine();
students[count2].setName(name);

System.out.print("Enter Student Address: ");
address= br.readLine();
students[count2].setAddress(address);

System.out.print("Enter Student Course: ");
course = br.readLine();
students[count2].setCourse(course);

System.out.print("Enter Student Year Level: ");
yr = br.readLine();
students[count2].setYr(yr);

count2++;

System.out.println("\nStudent Information");
System.out.println("ID:" + students[count].getID());
System.out.println("Name:" + students[count].getName());
System.out.println("Address: " + students[count].getAddress());
System.out.println("Course:" + students[count].getCourse());
System.out.println("Year Level:" + students[count].getYr());
break;

case 3:
schedules[count3] = new Schedules();
System.out.print("School Year: ");
sy = br.readLine();
schedules[count3].setSy(sy);

System.out.print("Enter Semester Level: ");
sem = br.readLine();
schedules[count3].setSem(sem);

System.out.print("Enter Section: ");
sec = br.readLine();
schedules[count3].setSec(sec);

System.out.print("Enter Subject Time for Lecture: ");
time1 = br.readLine();
schedules[count3].setTime1(time1);

System.out.print("Enter Subject Time for Laboratory: ");
time2 = br.readLine();
schedules[count3].setTime2(time2);

System.out.print("Enter Subject Day for Lecture: ");
day1 = br.readLine();
schedules[count3].setDay1(day1);

System.out.print("Enter Subject Day for Laboratory: ");
day2 = br.readLine();
schedules[count3].setDay2(day2);

System.out.print("Enter Room for Lecture: ");
rooms1 = br.readLine();
schedules[count3].setRooms1(rooms1);

Member 13996630 25-Sep-18 5:02am

System.out.print("Enter Room for Laboratory: ");
rooms2 = br.readLine();
schedules[count3].setRooms2(rooms2);

count3++;

System.out.println("Schedule Information");
System.out.println("School Year:" + schedules[count].getSy());
System.out.println("Semester Level:" + schedules[count].getSem());
System.out.println("Section:" + schedules[count].getSection());
System.out.println("Time Lecture:" + schedules[count].getTime1());
System.out.println("Time Laboratory:" + schedules[count].getTime2());
System.out.println("Day:" + schedules[count].getDay1());
System.out.println("Day:" + schedules[count].getDay2());
System.out.println("Rooms:" + schedules[count].getRooms1());
System.out.println("Rooms:" + schedules[count].getRooms2());
break;

case 4:

default:
System.out.println("Wrong Choice!");

}

}
}
catch(Exception e){
}
System.out.println( "\nDo it again? y/n" );
input = scan.nextLine().toLowerCase();
exit = input.charAt(0);

if(exit=='n'){
System.out.println("---------------Overall Data----------------");
System.out.println("Student ID:");

for(int i=0; i<count;i++){
System.out.println(students[i].getID());
}
System.out.println("Student Name:");
for(int x=0; x<count;x++){
System.out.println(students[x].getName());
}
System.out.println("Student Address:");
for(int o=0; o<count;o++){
System.out.println(students[o].getAddress());
}
System.out.println("Student Course:");
for(int j=0; j<count;j++){
System.out.println(students[j].getCourse());
}
System.out.println("Student Year Level:");
for(int k=0; k<count;k++){
System.out.println(students[k].getYr());
}

System.out.println("--------------------------------------------");

System.out.println("Subject ID:");
for(int y=0; y<count2;y++){
System.out.println(subjects[y].getSubid());
}
System.out.println("Subject Code:");
for(int z=0; z<count2;z++){
System.out.println(subjects[z].getCode());
}
System.out.println("Subject Description(Lec):");
for(int a1=0; a1<count2;a1++){
System.out.println(subjects[a1].getLecdesc());
}
System.out.println("Subject Description(Lab):");
for(int b1=0; b1<count2;b1++){
System.out.println(subjects[b1].getLab());
}
System.out.println("Lecture Units:");
for(int e=0; e<=count2;e++){
System.out.println(subjects[e].getUnits1());
}
System.out.println("Laboratory Units:");
for(int f=0; f<count2;f++){
System.out.println(subjects[f].getUnits2());
}

Member 13996630 25-Sep-18 5:03am

System.out.println("--------------------------------------------");
System.out.println("School Year:");
for(int v=0; v<count;v++){
System.out.println(schedules[v].getSy());
}
System.out.println("Semester Level:");
for (int r=0; r<count3; r++){
System.out.println(schedules[r].getSem());
}
System.out.println("Subject time for Lecture:");
for(int d=0; d<count3;d++){
System.out.println(schedules[d].getTime1());
}
System.out.println("Subject time for Laboratory:");
for(int d1=0; d1<count;d1++){
System.out.println(schedules[d1].getTime2());
}
System.out.println("Subject day for Lecture:");
for(int c=0; c<count3;c++){
System.out.println(schedules[c].getDay1());
}
System.out.println("Subject day for Laboratory:");
for(int c1=0; c1<count3;c1++){
System.out.println(schedules[c1].getDay2());
}

System.out.println("Room Designated for Lecture:");
for(int g=0; g<count3;g++){
System.out.println(schedules[g].getRooms1());
}
System.out.println("Room Deisgnated for Laboratory:");
for(int g1=0; g1<count3;g1++){
System.out.println(schedules[g1].getRooms2());
}
}
}
}}

AstiAsti 25-Sep-18 7:01am

Why do you use count2 as an index when entering student data and count as an index when outputting student data? This seems problematic.

Member 13996630 25-Sep-18 9:17am

yes typo error sorry my bad :/ i change it now but it's still the same error sir

Richard Deeming 25-Sep-18 11:17am

One of the entries in the students array is null. You'll need to debug your code to find out why.

Member1x 26-Sep-18 3:21am

Does the print in your switch-case work correctly? I assume you changed the index from count (which you used for Subject) to count2 (which you used for Student). If everything prints correctly direct after input and you get the error later, than you seem to change the data inbetween.