import java.io.DataInputStream; class student { String name = new String(""); String sub[] = new String[4]; String roll = new String(" "); int marks[],i; String grade = new String(""); DataInputStream ds = new DataInputStream(System.in); void get() { System.out.println("Enter"); } void getdata() { System.out.println("Enter name of student: "); try { name = ds.readLine(); } catch(Exception e) {} System.out.println("Enter roll of student: "); try { roll = ds.readLine(); } catch(Exception e) {} for(i=1;i<=4;i++) { System.out.println("Enter Subject"+i+"of Student: "); try { sub[i] = ds.readLine(); } catch(Exception e) {} System.out.println("Enter Marks for Subject"+i); try { marks[i] = Integer.parseInt(ds.readLine()); } catch(Exception e) {} } } } class m_stud { public static void main(String a[]) { student[] s = new student[4]; int i=1; for(i=1;i<=4;i++) { s[i].get(); } } } this code doesnot work in java... it shows an error like Exception in thread "main" java.lang.NullPointerException at m_stud.main(m_stud.java:59). pls help

The statement student[] s = new student[4]; assigns s to an array of 4 student references. Each array element doesn't reference an actual object until you assign it to one.

thanx... now i understand my mistake...