So I'm running a program that does various things to a String array. One of them is a inserting a string inside the array and sorting it. I'm able to use the sort method, but when I attempt to insert a string and then sort it I get a NullPointerException. This is the code:
import java.util.Scanner;
import java.io.*;
public class List_Driver
{
public static void main(String args[])
{
Scanner keyboard = new Scanner(System.in);
int choice = 1;
int checker = 0;
String [] words = new String[5];
words[0] = "telephone";
words[1] = "shark";
words[2] = "bob";
ListWB first = new ListWB(words);
int menu = uWB.getI("1. Linear Seach\n2. Binary Search\n3. Insertion in Order\n4. Swap\n5. Change\n6. Add\n7. Delete\n8. Insertion Sort\n9. Quit\n");
switch(menu)
{
//other cases
case 3:
{
String insert = uWB.getS("What term are you inserting?");
first.insertionInOrder(insert);
first.display();
}//not working
break;
}//switch menu
}//main
}//List_Driver
uWB is a basic util driver. It doesn't have any problems. This is the ListWB file itself:
public class ListWB
{
public void insertionSort()
{
for(int i = 1; i < size; i++)
{
String temp = list[i];
int j = i;
while(j > 0 && temp.compareTo(list[j-1])<0)
{
list[j] = list[j-1];
j = j-1;
}
list[j] = temp;
}
}
public void insertionInOrder(String str)
{
insertionSort();
int index = 0;
if(size + 1 <= list.length)
{
while(index < size && str.compareTo(list[index])>0)
index++;
size++;
for (int x = size -1; x> index; x--)
list[x] = list[x-1];
list[index] = str;
}
else
System.out.println("Capacity Reached");
}//insertioninorder
}//ListWB
How would I fix this?
You have an array of 5 Strings, but only 3 of them initialized. The rest points to null (because you did not initialize them):
String [] words = new String[5];
words[0] = "telephone";
words[1] = "shark";
words[2] = "bob";
words[3] = null;
words[4] = null;
The first line only initializes the array itself, but not the containing objects.
But the insert iterates over all 5 elements. And temp is null, when i is 3. So the statement temp.compareTo throws an NullPointerException.
for(int i = 1; i < size; i++)
{
String temp = list[i];
int j = i;
while(j > 0 && temp.compareTo(list[j-1])<0)
Solution: Also check temp for null in the while loop. Or do not use a string array at all but a auto-resizable data structure list java.util.ArrayList.
Related
Hello I've been getting this error in Kattis, 'Run time error' while all my test cases are correct in my own machine. Tested everything but as soon as i run this in kattis i get a run time error. Can you guys help me figure this out? Ive been debugging for hours but i am struggling.
https://open.kattis.com/problems/throwns?editsubmit=9372235 :Link of the problem
import java.util.*;
import java.io.*;
public class GOT{
public static void main(String[] args)throws IOException{
BufferedReader bi = new BufferedReader(new I
nputStreamReader(System.in));
int[] parseLine1 = new int[2];
String[] strLine1;
strLine1 = bi.readLine().split(" ");
//Parsing of 1st line of inputs i.e. N and K
for (int i = 0; i < strLine1.length; i++) {
parseLine1[i] = Integer.parseInt(strLine1[i]);
}
//init of Kids array
int[] nKids = new int[parseLine1[0]];
String[] commands = new String[parseLine1[1]];
int i;
for(i = 0; i < nKids.length; i++){
nKids[i] = i;
}
//parsing of 2nd line which are the commands
String strLine2;
String[] nCommands;
Scanner sc = new Scanner(System.in);
strLine2 = sc.nextLine();
nCommands = strLine2.split(" ");
int holder=0;
ArrayList<Integer> tracker = new ArrayList<Integer>();
int exit;
int throwns;
int undoCtr=0;
for(i = 0; i<nCommands.length; i++){
if(nCommands[i].equals("undo")){
nCommands[i] = nCommands[i].replaceAll("undo","101");
}
}
exit = nCommands.length;
i = 0;
while(exit != 0){
//System.out.println(Integer.parseInt(nCommands[i]));
if(Integer.parseInt(nCommands[i]) > 0){
for(int k = 0; k< Integer.parseInt(nCommands[i]); k++){
holder++;
if(holder==nKids.length){
holder = 0;
}
}
}if(Integer.parseInt(nCommands[i]) < 0){
for(int k = Integer.parseInt(nCommands[i]); k<0 ; k++){
holder--;
if(holder==0){
holder = nKids.length;
}
}
}else if(Integer.parseInt(nCommands[i]) == 101){
i++;
undoCtr = Integer.parseInt(nCommands[i]);
while(undoCtr!=0){
tracker.remove(tracker.size()-1);
undoCtr--;
}
exit--;
}
tracker.add(holder);
exit--;
i++;
}
System.out.println(tracker.get(0));
}`
}`
Your approach is too complex for a 2.8 difficulty problem. If you find yourself writing more than 25 lines of code, it's usually time to take a step back and re-think your approach.
Here's the algorithm that worked for me:
Make a list of "final" throw commands, initially empty.
Loop over the input tokens and analyze each command:
If a command is a number, append to the command list.
If a command is an undo n, pop the command list n times.
Now sum the commands in the list and print the mod of this sum, taking care to keep the mod positive.
Here's the spoiler:
public class Throwns {
public static void main(String[] args) {
var sc = new java.util.Scanner(System.in);
int n = Integer.parseInt(sc.nextLine().split(" ")[0]);
var line = sc.nextLine().split(" ");
var commands = new java.util.ArrayList<Integer>();
int sum = 0;
for (int i = 0; i < line.length; i++) {
if (line[i].matches("^-?\\d+$")) {
commands.add(Integer.parseInt(line[i]));
continue;
}
for (int j = Integer.parseInt(line[++i]); j > 0; j--) {
commands.remove(commands.size() - 1);
}
}
for (int c : commands) {
sum += c;
}
System.out.println(Math.floorMod(sum, n));
}
}
Hello I can't make this work, I am given a main word followed by another sub words if the word is contained in the main word the part should be deleted.
//Example
//fmrog (in.nextLine)(main word)
//4 (in.nextInt)(the amount of sub words)
//roc(in.nextLine)(not contained)
//gor(in.nextLine)(not contained)
//rog(in.nextLine)(contained)
//ogr(in.nextLine)(not contained)
//result:fm
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
StringBuilder mainWord = new StringBuilder(in.nextLine);
int n = in.nextInt();
StringBuilder MainWord2 = new StringBuilder(mainWord);
in.nextLine();
for (int i = 0; i < n; i++) {
String subWord = in.nextLine();
int chars = subWord.length();
if (chars> mainWord.length()){
continue;
}
for (int j = 0; j < subWord.length(); j++) {
int r = 0;
for (int k = 0; k < mainWord.length(); k++) {
r++;
if (k > MainWord2.length() - 1) {
break;
}
if (MainWord2.charAt(k) == subWord.charAt(j)) {
break;
}
}
if (r <= MainWord2.length() && MainWord2.charAt(r-1) == subWord.charAt(j)) {
MainWord2.deleteCharAt(r - 1);
if (j >= subWord.length() -1 ) {
mainWord = MainWord2;
break;
}
}
if (r > MainWord2.length()) {
MainWord2 = mainWord;
break;
}
}
}
System.out.println(mainWord);
}
}
Honestly I am stucked maybe there is an easier way to solve this. The main thing is that when I write a case like : "super 2 pe surr" At the end at "surr" the two StringBuilders start to act as one when I delete chatAt at one of them the other one changes also
No need to make it so complex.
String input = // complete user input
String[] words = String.split(input);
String mainWord = words[0];
int numWords = Integer.parseInt(words[1]); // this variable isn't needed
for(int i = 2; i < words.length; i++) {
if (mainWord contains words[i]) {
mainWord = mainWord.replace(words[i], ""); // remove subword from mainword
}
}
At the end, mainWord will be the original mainWord without any subwords that were entered later.
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
in.nextLine();
String[] words = new String[n];
for (int i = 0; i <n ; i++) {
words[i] = in.nextLine();
}
String mainWord = words[0];
for (int i = 1; i <words.length ; i++) {
if (mainWord.contains(words[i])){
mainWord = mainWord.replace(words[i], "");
}
}
System.out.println(mainWord);
}
}
Here but the thing is if the letters are not one next to another it doesnt remove the subword.
I am trying to run a loop to see if an int is sorted. however the int has to be converted from a string. here is my code.
public static void main(String[] args) {
// TODO code application logic here
Scanner maxVal = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
System.out.println("enter the max value of ordered squares:");
int max = maxVal.nextInt();
for(int i = 0; i*i <= max; i++){
int L = String.valueOf(i*i).length();
String sq = String.valueOf(i*i);
String [] digits = new String[L];
for(int a = 0; a < L; a++){
digits [a] = Character.toString(sq.charAt(a));
if(L == 1){
System.out.print(sq + "");
}else if(Integer.parseInt(digits [a]) < Integer.parseInt(digits[a+1])){
System.out.print(sq);
}else{
}
}
}
}
when I run it, I get an error :
Exception in thread "main" java.lang.NumberFormatException: null
0149 at java.lang.Integer.parseInt(Integer.java:542)
at java.lang.Integer.parseInt(Integer.java:615)
why does Integer.parseInt() not work
Your problem is that digits[a+1] hasn't been defined yet. I see that on line 2 you have
digits[a] = Character.toString(sq.charAt(a));
and you're iterating over a in a for loop, so I daresay that digits[a+1] hasn't been assigned yet.
UPDATE 1
Check out this solution, it shows how to properly catch that exception and how to avoid it:
Java: Good way to encapsulate Integer.parseInt()
UPDATE 2
I decided to add a fixed version of your code:
public static void main(String[] args) {
// TODO code application logic here
Scanner maxVal = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
System.out.println("enter the max value of ordered squares:");
int max = maxVal.nextInt();
for(int i = 0; i*i <= max; i++){
int L = String.valueOf(i*i).length();
String sq = String.valueOf(i*i);
String [] digits = new String[L];
for(int a = 0; a < L; a++){
digits [a] = Character.toString(sq.charAt(a));
if(L == 1 || a == 0){
System.out.print(sq + "");
}else if(Integer.parseInt(digits [a]) < Integer.parseInt(digits[a+1])){
System.out.print(sq);
}else{
}
}
}
}
While I don't know the utility of your code, but this implementation might be simpler:
public static void main(String[] args) {
// TODO code application logic here
Scanner maxVal = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
System.out.println("enter the max value of ordered squares:");
int max = maxVal.nextInt();
for(int i = 0; i*i <= max; i++){
long sq = i*i;
if(sq > 9){
String[] digits = sq.toString().split("");
//Notice that I start at index 1, so I can do [a-1] safely
for(int a = 1; a < digits.length; a++){
if(Integer.parseInt(digits [a-1]) < Integer.parseInt(digits[a])){
System.out.print(sq);
//I guess we don't want a number like 169 (13*13) to be displayed twice, so:
break;
}
}
} else {
System.out.print(sq);
}
}
}
I need help sorting this array in alphabetical order using the bubble sort algorithm.
My code is:
public class Strings
{
public static void main(String[] args)
{
Scanner reader = new Scanner(System.in);
String tempStr;
System.out.print("Enter the strings > ");
String s1 = new String(reader.nextLine());
String[] t1 = s1.split(", ");
for (int t=0; t<t1.length-1; t++)
{
for (int i = 0; i<t1.length -1; i++)
{
if(t1[i+1].compareTo(t1[1+1])>0)
{
tempStr = t1[i];
t1[i] = t1[i+1];
t1[i+1] = tempStr;
}
}
}
for(int i=0;i<t1.length;i++)
{
System.out.println(t1[i]);
}
}
}
The code compiles, but it does not sort alphabetical. Please help me.
You have three errors in your code.
The first error is in the inner for loop, in the place where you do the check statement, it should be i < t1.length - t -1 not i < t1.length -1. You subtract t because you do not want to loop through the whole array again, only the first part of it.
The second and third errors are in the if statement. You need to turn the greater than symbol into a lesser than symbol, because the way you have the compareTo method set up, it will return a negative number.
The other error in this line is that in the compareTo parameter you put 1 + 1 it actually should be just i, because you want one less than the object it is comparing to.
The fixed working code is below (Comments are what you originally had):
public static void main(String[] args) {
Scanner reader = new Scanner(System.in);
String tempStr;
System.out.print("Enter the strings > ");
String s1 = new String(reader.nextLine());
String[] t1 = s1.split(", ");
for (int t = 0; t < t1.length - 1; t++) {
for (int i= 0; i < t1.length - t -1; i++) {
if(t1[i+1].compareTo(t1[i])<0) {
tempStr = t1[i];
t1[i] = t1[i + 1];
t1[i + 1] = tempStr;
}
}
}
for (int i = 0; i < t1.length; i++) {
System.out.println(t1[i]);
}
}
please change
String[] t1 = s1.split(", ");
to
String[] t1 = s1.split("");
This will solve the issue.
StackOverflow. I am attempting to make a program that uses a text menu to to a multitude of things to manipulate a single string. One of the methods turns the string into an array of strings. This works fine. However, all of the methods that manipulate it as an array(one prints it out, one reverses the word order, and one sorts them using an exchange sorting method) return a NullPointerException when called. I have looked all through the code and do not see where it is coming from. Here is the .Java file containing all of the code. My problem is only happening when I call the printArray(), reverse(), and sort() methods, near the bottom. Any and all help is appreciated. Sorry for the sloppy code, I have not cleaned it up yet.
Code:
/*
Computer Programming Lab 11
Jim Kimble
3 Mar 2013
Work with strings and implementing a menu.
Acknowledgements:
Uses main structure of HUTPanel as designed at UMU, 2002-2012
*/
import java.io.*;
import java.awt.*;
import javax.swing.*;
public class HUTPanel extends JPanel
{
/***************************************************
* Class-level data members should be declared here.
***************************************************/
int numVowels;
String[] words;
String str;
String vowels;
String menuChoice;
String oString = "A tong lime ago, a daggy shog bossed a cridge over a pillmond,\n"
+"When in the course of human events\n"
+"Mary had a little lamb.\n"
+"The girls' basketball team repeated as tournament champion this weekend.";
public HUTPanel(JFrame frame)
{
// Set panel background color
setBackground(Color.WHITE);
setLayout(null);
setPreferredSize(new Dimension(810, 410));
/***************************
* Now add your code below:
***************************/
// Create a frame around this panel.
frame.setTitle("Computer Programming Lab/Program # 11");
frame.getContentPane().add(this);
str = "A tong lime ago, a daggy shog bossed a cridge over a pillmond,\n"
+"When in the course of human events\n"
+"Mary had a little lamb.\n"
+"The girls' basketball team repeated as tournament champion this weekend.";
System.out.println("Lab 11: Text Manipulation");
//getTheText();
System.out.println("The string is: '"+str+"'.");
handleTheMenu();
} // end of constructor
/*************************
* Add your methods here:
*************************/
// Get a text sequence from the keyboard and put it in str
public void getTheText()
{
Boolean inputDone = false;
while (!inputDone)
{
System.out.print("Enter your text: ");
inputDone = grabText();
}
}
private Boolean grabText()
{
try {
BufferedReader inputReader = new BufferedReader(new InputStreamReader(System.in));
menuChoice = inputReader.readLine();
return true;
}
catch(IOException e)
{
System.out.println("Error reading input. Please try again.");
}
return false;
}
public void handleTheMenu()
{
int choice = -1;
Boolean OK;
while (choice != 0)
{
choice = -1;
System.out.println("Menu:");
System.out.println();
System.out.println(" 1. Count the vowels"); //"There are ... vowels in the text."
System.out.println(" 2. Remove all letter e's"); //then print it.
System.out.println(" 3. Replace all t's with '+'"); //then print it
System.out.println(" 4. Search for a requested word (will reset the string)"); //Does 'word' exist in the text?
System.out.println(" 5. Print the words on individual lines");
System.out.println(" 6. Reset the string.");//Reset the string to the original
System.out.println(" 7. Put the words in an array"); //then print it
System.out.println(" 8. Reverse the text word order"); //then print it
System.out.println(" 9. Sort the words in an array"); //Once the words are put into an array
System.out.println();
System.out.print(" 0 to quit --> ");
OK = grabText();
if (OK)
{
try
{
choice = Integer.parseInt(menuChoice);
}
catch(NumberFormatException e)
{
System.out.println("Not a number; please try again.");
System.out.println();
}
switch(choice)
{
case 0: System.out.println();
System.out.println("Thank you.");
break;
case 1: countVowels();
break;
case 2: removeAllEs();
break;
case 3: changeTToPlus();
break;
case 4: find();
break;
case 5: listWords();
break;
case 6: reset();
break;
case 7: makeArray();
break;
case 8: reverse();
break;
case 9: sort();
break;
default: System.out.println("Not a valid choice; please try again.");
}
}
}
}
private void countVowels() {
//count the vowels in str
vowels = "aeiouAEIOU";
numVowels = 0;
for( int i = 0; i < vowels.length(); i ++) {
for(int j = 0; j < str.length(); j++) {
if (str.charAt(j) == vowels.charAt(i)) {
numVowels += 1;
}
}
}
System.out.println("The string has " + numVowels + " vowels in it.");
}
private void removeAllEs() {
String str3 = str.replace('e', ' ');
System.out.print(str3);
str = str3;
}
private void changeTToPlus() {
String str2 = str.replace('t', '+');
System.out.println(str2);
str = str2;
}
private void find() {
str = oString;
getTheText();
if(str.indexOf(menuChoice) != -1)
{
System.out.println("The word " +menuChoice+ " is at index " +str.indexOf(menuChoice));
}
else
{
System.out.println("The word " +menuChoice+ " is not in the string.");
}
}
private void listWords() {
int pos = 0;
int i = 0;
while(i > -1)
{
i = str.indexOf(' ', pos);
if (i > -1)
{
System.out.println(str.substring(pos, i));
pos = i + 1;
}
}
}
private void reset() {
str = oString;
System.out.println();
System.out.println("String reset.");
System.out.println();
}
private void makeArray() {
int n = 1;
String[] words = new String[n];
int pos = 0;
int i = 0;
int j = 0;
while(j > -1)
{
for (i = 0; i < 1000; i++)
{
n += 1;
j = str.indexOf(' ', pos);
if (j > -1)
{
words[i] = str.substring(pos, j);
pos = j + 1;
}
}
}
//printArray();
}
//***FIX***
private void printArray() {
for (int k = 0; k < words.length -1; k++){
System.out.println(words[k]);
}
}
//***FIX***
private void reverse() {
int i = 0;
int j = words.length - 1;
String temp;
while (i < j){
temp = words[i];
words[i] = words[j];
words[j] = temp;
i++;
j--;
}
}
private void sort() {
String temp = "";
for (int i = 1; i < words.length - 1; i++) {
for (int j = i + 1; j < words.length; j++) {
int x = words[i].compareTo(words[j]);
if (x > 0) {
temp = words[i];
words[i] = words[j];
words[j] = temp;
}
}
}
for (int p = 0; p < words.length -1; p++) {
System.out.println(words[p]);
}
}
}
You Error is here:
private void makeArray() {
int n = 1;
String[] words = new String[n];//At This line you are creating local array words.The instance variable words is still null.
int pos = 0;
int i = 0;
int j = 0;
while(j > -1)
{
for (i = 0; i < 1000; i++)
{
n += 1;
j = str.indexOf(' ', pos);
if (j > -1)
{
words[i] = str.substring(pos, j);
pos = j + 1;
}
}
}
use:
words = new String[n]; instead of String[] words = new String[n];
As mentioned by Luiggi Mendoza in the comment section, the local variable words defined within makeArray method is shadowing the instance variable words defined within HUTPanel class.
As side note I want to point out the unnecessary creation of new BufferedReader objects in method grabText() each time you are calling it in getTheText(). It would be much efficient if your make inputReader an instance variable in your class , and instantiate it once within the constructor using inputReader = new BufferedReader(new InputStreamReader(System.in));. This way your grabText method becomes like this :
private Boolean grabText()
{
try {
//No more new object creation for BufferedReader for each call of this method.
menuChoice = inputReader.readLine();
return true;
}
catch(IOException e)
{
System.out.println("Error reading input. Please try again.");
}
return false;
}
Make sure you always you always start with option 7, so your words array gets initialized. This is in fact not something that the user should do. The application should handle it so that the user either can't select other options, or does it automatically.
Update: Vishal K is correct, but this is still a weak point in your application.