Null pointer exception
I have written a program which reads file into a binary search tree.
I used string tokenizer to split the text into stringpart and int part.
I gives me null pointer exception.
Can anyone help me so the the file will red inorder binary search tree.
class CityNode
{
String name;
int temperature;
protected CityNode left;// left node
protected String d;// data item
protected CityNode right; // right node.
CityNode(String d) // Constructor
{
d = null;
left = right = null;
}
}
public class City
{
private String name;
private int temperature;
// The root node of the tree initialised here to null
public CityNoderoot;
//public City(String nameIn, int temperatureIn)
//{ }
private CityNode insert(String d, int temp)
{
name = d;
temperature = temp;
root = null;
// insert a node into tree
// void insert(String d)
CityNode current = root;
CityNode prev = current;
if(root == null) {
root = new CityNode(d);
}
else{
boolean insert = false;
while(insert == false){
prev = current;
if (d.compareTo(current.d)<0) {
if (current.left == null){
current.left = new CityNode(d);
insert = true;
}
current = current.left;
}
else{
if (current.right == null){
current.right = new CityNode(d);
insert = true;
}
current =current.right;
}
}
}
return root;
}
// public String getName() { return name; }
// Return a student's age
// public int getTemperature() { return temperature; }
//in order
CityNode inord(CityNode tree) {
int t = 0;
CityNode ret;
CityNode prev;
// prev = new CityNode();
prev = tree;
tree = tree.right;
while (tree.left != null) {
prev = tree;
tree = tree.left;
t = 1;
}
ret = tree;
if (t == 0) {
prev.right = null;
}
else {
prev.left = null;
}
tree = null;
return ret;
}
//print the node
public void printIn(CityNode oot) {
if (oot.left != null) {
printIn(oot.left);
}
System.out.println("--" + oot.d + "-");
if (oot.right != null) {
printIn(oot.right);
}
}
}
import java.util.*;
import java.io.*;
public class CityTest
{
static BufferedReader fileInput;
public static void main( String args[ ] )throws IOException
{
String inputString;
String name;
int temperature, i =0;
StringTokenizer tokens;
// I assmume only 4 students as was indicated in the tutorial
City [] sArray = new City[30];
fileInput = new BufferedReader( new FileReader("Citys.dat"));
inputString = fileInput.readLine();
// read the file until null is returned
while(inputString != null)
{
// First you need to split the string using the String Tokenizer
tokens = new StringTokenizer(inputString);
name = tokens.nextToken(); // I have extracted the first component
temperature = Integer.parseInt(tokens.nextToken());
City tree = new City();
System.out.println ( "\n\nInorder " );
//tree.inord();
tree.printIn(tree.root);
}
}
}
