Problem with array

Hi,
when i run my program, it shows this
"Exception in thread "main" java.lang.NullPointerException"
but my array doesn't not contain any null value, how can i check if the array is null or not, or where is the null value contain? how can i solve this?
Thank you for helping

Post an SSCCE.

You can just do a check against null (someObject == null), but I would bet that you have a more fundamental problem.

This is the code

Code Java:

---

import java.io.*;
 
public class P {
	public static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static int [][] Graph;
	public static int [][] Tree;
        public static tempEdge [] tedges;
        private static int tempi = 0, one, two, size;
 
        public void buildTable(String file){
            n = 5;
            tedges = new tempEdge[n*(n-1)/2];
            try{
                BufferedReader input = new BufferedReader(new FileReader(file));
                while(input.ready())
                {
                   String tmp = input.readLine();
                   String[] newPoint = tmp.split(" ");
                   int p1 = Integer.parseInt(newPoint[0]);
                   int p2 = Integer.parseInt(newPoint[1]);
                   int dis = Integer.parseInt(newPoint[2]);
                   tedges[tempi] = new tempEdge(p1,p2,dis);
                   System.out.println(tedges[tempi].firstPoint());
                   System.out.println(tedges[tempi].secondPoint());
                   System.out.println(tedges[tempi].distance());
                   tempi++;
                 }
            }
            catch(IOException e)
            {
		System.out.println("Error, file does not exist");
            }
            p();
        }
        //create a minal spanning tree
	public static void p()
	{
                n = 5;
                //set size of the array which store different things
		Graph = new int[n+1][n+1];
		Tree = new int[n+1][3];
 
                while(tedges != null){
                   for(int i=0;i<=tedges.length;i++){
                        //tempEdge e = tedges[i];
                            one = tedges[i].firstPoint();
                            two = tedges[i].secondPoint();
                            size = tedges[i].distance();
                            if((one!=two)&&(one<two)) {
                                Graph[one][two] = Graph[two][one] = size;
                            }
                    }
	}
 
.....
 
        public static void main (String[] args) throws IOException
        {
               P p = new P();
               p.buildTable("3Dtriangle.txt");
	}
}

---

and the file "3Dtriangle.txt" contains
1 2 50
1 3 30
1 4 20
2 3 15
2 4 45
3 4 60

I don't know why when the program goes to p(), then it will stops and said
"Exception in thread "main" java.lang.NullPointerException"

Put some print statements in there, or step through it with a debugger. I'd bet that it's not actually entering all of the methods you think it is.

Hint: What does a constructor declaration look like?

Also, you really should follow standard naming conventions. Classes start with an uppercase letter, and methods and variables start with a lowercase letter. Using more descriptive names wouldn't hurt either.

String[] newPoint = tmp.split(" ");

Why would an entire String array be set to a single String value?

int p1 = Integer.parseInt(newPoint[0]);
int p2 = Integer.parseInt(newPoint[1]);
int dis = Integer.parseInt(newPoint[2]);

You never set the value for newPoint[0], newPoint[1], and newPoint[2].

That's likely the cause of the Null Pointer Exception.

Quote:

---

Originally Posted by mingming8888

This is the code

Code Java:

---

import java.io.*;
 
public class P {
	public static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static int [][] Graph;
	public static int [][] Tree;
        public static tempEdge [] tedges;
        private static int tempi = 0, one, two, size;
 
        public void buildTable(String file){
            n = 5;
            tedges = new tempEdge[n*(n-1)/2];
            try{
                BufferedReader input = new BufferedReader(new FileReader(file));
                while(input.ready())
                {
                   String tmp = input.readLine();
                   String[] newPoint = tmp.split(" ");
                   int p1 = Integer.parseInt(newPoint[0]);
                   int p2 = Integer.parseInt(newPoint[1]);
                   int dis = Integer.parseInt(newPoint[2]);
                   tedges[tempi] = new tempEdge(p1,p2,dis);
                   System.out.println(tedges[tempi].firstPoint());
                   System.out.println(tedges[tempi].secondPoint());
                   System.out.println(tedges[tempi].distance());
                   tempi++;
                 }
            }
            catch(IOException e)
            {
		System.out.println("Error, file does not exist");
            }
            p();
        }
        //create a minal spanning tree
	public static void p()
	{
                n = 5;
                //set size of the array which store different things
		Graph = new int[n+1][n+1];
		Tree = new int[n+1][3];
 
                while(tedges != null){
                   for(int i=0;i<=tedges.length;i++){
                        //tempEdge e = tedges[i];
                            one = tedges[i].firstPoint();
                            two = tedges[i].secondPoint();
                            size = tedges[i].distance();
                            if((one!=two)&&(one<two)) {
                                Graph[one][two] = Graph[two][one] = size;
                            }
                    }
	}
 
.....
 
        public static void main (String[] args) throws IOException
        {
               P p = new P();
               p.buildTable("3Dtriangle.txt");
	}
}

---

and the file "3Dtriangle.txt" contains
1 2 50
1 3 30
1 4 20
2 3 15
2 4 45
3 4 60

I don't know why when the program goes to p(), then it will stops and said
"Exception in thread "main" java.lang.NullPointerException"

---

Also, I'm not sure if it'll know the new value that you've set for tedges in buildTable when you use tedges in p.

i have tried to run it, and i got the result below
1
2
50
1
3
60
1
4
70
2
3
80
Exception in thread "main" java.lang.NullPointerException
2
4
40
3
4
60
1
1
1
1
1
1
It shows that tedges[] can read from the file, but i am not sure why there is null value?

Please post the entire stack that is printed to the console when the exception is thrown

u mean this??

at triangle_projection.P.p(Prim.java:69) - for(int i=0;i<=tedges.length;i++)
at triangle_projection.P.buildTable(Prim.java:55) - p();
at triangle_projection.P.main(Prim.java:178) - p.buildTable("3Dtriangle.txt");

That is not the full stack, but it looks like it is part of it