Develop Reference

Easy fix for while loop not executing properly second time?

I'm fairly new at java and have a current assignment to take a given word, put the first word at the end, rebuild the word from reverse, and see if it's the same word as the original, such as: grammar, potato, uneven, dresser, banana etc. So far I have this:
Scanner input = new Scanner(System.in);
String original, reverse = "";
String exit = "quit";
int index;
System.out.println("Please enter a word (enter quit to exit the program): ");
original = input.next();
while (!original.equalsIgnoreCase(exit))
{
String endingChar = original.substring(0, 1);
String addingPhrase = original.substring(1);
reverse += endingChar;
for (index = addingPhrase.length() - 1; index >= 0; --index)
{
char ch = addingPhrase.charAt(index);
reverse += ch;
}
if (original.equals(reverse))
{
System.out.println("Success! The word you entered does have the gramatic property.");
}
else
{
System.out.println("The word you entered does not have the gramatic property."
+ " Please try again with another word (enter quit to exit the program): ");
}
original = input.next();
}
input.close();
When I run it and enter the word "banana," it properly recognizes that it is indeed the same backwards when the b is moved to the end, and does the same with the other words listed above, but when I enter a second word on the loop, it never recognizes it properly, and always responds with the print statement from the else block:
Please enter a word (enter quit to exit the program):
banana
Success! The word you entered does have the gramatic property.
banana
The word you entered does not have the gramatic property. Please try again
with another word (enter quit to exit the program):
I'm guessing it's something to do with either the way I made my for loop, or the way I asked for input at the end of the while loop, but like I said I'm fairly new and awful at debugging. Any help would be much appreciated, thanks a lot in advance.

You are changing string reverse in every iteration, but you are not clearing it. So before the end of the loop or at the beginning clear the string for example like so: reverse = "", and then it should be fine.

Just add reverse = ""; in the end of the while loop in order to set the variable reverse to its original state, i.e. empty string

Regular Expression in Java: Validating user input

I am trying to validate user input using a regular expression in a while loop. I am trying to accept only one lower-case word (letters a-z inclusive).
public class testRedex{
public static void main(String [] args){
Scanner console = new Scanner(System.in);
System.out.print("Please enter a key: ");
while(!console.hasNext("[a-z]+")){
System.out.println("Invalid key");
console.next();
}
String test = console.next();
System.out.println(test);
}
}
My question is, is there any difference between having the regular expression as "[a-z]+" and "[a-z]+$"? I know that $ will look for a character between a-z at the end of the string, but in this case would it matter?

Yes there is a difference, if you'll use: ^[a-z]+$ it means that whatever the user inputs should be combined only from [a-z]+.
If you don't add the ^ and the $ the user could insert other characters, space for example, and there will still be a match (the first part of the string until the space.
Let's see an example:
run your code with the input: "try this" (it'll print "try")
now change the regex to ^[a-z]+$ and run with the same input (it'll print "Invalid key").
The way I would re-write it is:
System.out.print("Please enter a key: ");
String test = console.nextLine();
while (!test.matches("^[a-z]+$")) {
System.out.println("Invalid key");
test = console.nextLine();
}
System.out.println(test);

The difference are as follows
[a-z]+ means a,b,c,...,or z occurs more than one time
[a-z]+$ means a,b,c,...,or z occurs more that one time and must match end of the line
Yet at the end, they give you the same result.
if you want to understand it better try this
([A-Z])([a-z]+$)
It start with a capital letter and end with more than one time small letter
output:
Please enter a key: AAAAaaaa
Invalid key
Aaaaaa
Aaaaaa
Another way you can get the expected result from what you are looking for
code:
int i = 0;
String result = "";
do{
Scanner input = new Scanner(System.in);
System.out.println("Enter your key:");
if(input.hasNext("^[a-z]+$")){
result = input.next();
i=1;
}else{
System.out.println("Invalid key");
}
}while(i==0);
System.out.println("the result is " + result);
output:
Enter your key:
HHHh
Invalid key
Enter your key:
Hellllo
Invalid key
Enter your key:
hello
the result is hello

ArrayIndexOutOfBoundsException on a Split String in a array

So I am doing some problems on the UVa online problem judge, but on a relativity easy problem, I keep on getting a ArrayIndexOutOfBoundsException. To understand the code, here is the problem.
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int t = scan.nextInt();
int sum = 0;
for (int i = 0; i <= t; i++){
String d = scan.nextLine();
if (d.equals("report")) {
System.out.println(sum);
} else {
String[] parts = d.split(" ");
int z = Integer.parseInt(parts[1]);
sum+=z;
}
}
}
}
The error message is:
reportException in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at Main.main(Main.java:16)
And I am using the sample input given.
Edit:
I have already tried added println statements in the code and figured out that the number is not being read. I am trying to understand why.

OK, after some messing around on my machine I think I found what might be at least part of the problem. The issue is that I'm not sure what the precise input is, so I'm going off of what I could get working on my machine.
So you start up your program, and it waits for a prompt at this line:
int t = scan.nextInt();
You enter your integer, and the program moves on as expected:
Input: 100 // Then press enter to continue
The input is parsed, and now t is set to 100.
Then when your program enters your for loop, it comes across this line:
String d = scan.nextLine();
Yet for some reason the program doesn't wait for input! (Or at least it didn't on my machine)
I believe the issue lies here:
Input: 100 // Then press enter to continue
^^^^^^^^^^^
What I think is happening is that your input is really
Input: 100\n
^^
That character (\r\n on Windows) is what's input when you hit enter. It's a newline character that tells the console to go to the next line.
So as a result, what I think happens is this:
Input: 100\n
Scanner parses 100, leaving the \n in the input stream
Then at the nextLine() call, the scanner sees \n on the input stream, which denotes end of line, so it thinks you already input the entire line! Because what it thought was your input was only the newline character, it returns an empty string, because your "input" was an empty string and the newline character. Your program then goes to split the newline character by spaces, rightly returns an array with a single element, and then your program promptly crashes when accessing an out-of-bounds index.
What might work better is reading an entire line first and parsing the integer so your scanner doesn't get ahead of itself, like this:
int t = Integer.parseInt(scan.nextLine());
Just as a warning: This is what I've been able to come up with based on using OP's code as-is on my machine. I was unable to get a situation where the only element in parts was "donate". I will update further as I get more info.

The error message means the array parts's length less than 2, sometimes.
It means the variable d does not always contain the string BLANK SPACE, " ", what you split by.
try this code:
import java.util.Arrays;
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int t = scan.nextInt();
int sum = 0;
for (int i = 0; i <= t; i++){
String d = scan.nextLine();
if (d.equals("report")) {
System.out.println(sum);
} else {
String[] parts = d.split(" ");
/*
* Add IF statement,
*/
if (parts.length() > 1) {
int z = Integer.parseInt(parts[1]);
sum+=z;
}
}
}
}
}

Adding Spaces between words and making every word except the first lowercase in java

I'll go ahead and let you know that yes, this is homework. I have hit a brick wall in completing it however and desperately need help. I'm also pretty new to Java and am still learning the language.
Okay, I am trying to write a program that asks the user to enter a sentence with no spaces but have them capitalize the first letter of each word. The program should then add spaces between the words and have only the first word capitalized, the rest should start with a lowercase. I can get the space inserted between the words, but I cannot get the first letter of each word lower-cased. I have tried several different ways, and the latest one is giving me this error message:
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String ind
ex out of range: 72
at java.lang.AbstractStringBuilder.setCharAt(Unknown Source)
at java.lang.StringBuilder.setCharAt(Unknown Source)
at renfroKristinCh9PC14.main(renfroKristinCh9PC14.java:45)
I'm posting up my code and any and all help you can give me will be very much appreciated.
Thanks.
/*
This program will ask the user to enter a sentence without whitespaces, but
with the first letter of each word capitilized. It will then separate the words
and have only the first word of the sentence capitalized.
*/
import java.util.*;
public class renfroKristinCh9PC14
{
public static void main(String[] args)
{
//a string variable to hold the user's input and a variable to hold the modified sentence
String input = "";
//variable to hold a character
char index;
//create an instance of the scanner class for input
Scanner keyboard = new Scanner(System.in);
//welcome the user and explain the program
userWelcome();
//get the sentence from the user
System.out.println("\n Please enter a sentence without spaces but with the\n");
System.out.println(" first letter of each word capitalized.\n");
System.out.print(" Example: BatmanIsTheBestSuperheroEver! ");
input = keyboard.nextLine();
//create an instance of the StringBuilder class
StringBuilder sentence = new StringBuilder(input);
//add spaces between the words
for(int i=0; i < sentence.length(); i++)
{
index = sentence.charAt(i);
if(i != 0 && Character.isUpperCase(index))
{
sentence.setCharAt(index, Character.toLowerCase(index));
sentence.append(' ');
}
sentence.append(index);
}
//show the new sentence to the user
System.out.println("\n\n Your sentence is now: "+sentence);
}
/*********************************************************************************** *************************
************************************************************************************ *************************
This function welcomes the user and exlains the program
*/
public static void userWelcome()
{
System.out.println("\n\n **************** ****************************************************\n");
System.out.println(" * Welcome to the Word Seperator Program *");
System.out.println(" * This application will ask you to enter a sentence without *");
System.out.println(" * spaces but with each word capitalized, and will then alter the *");
System.out.println(" * sentence so that there arespaces between each word and *");
System.out.println(" * only the first word of the sentence is capitalized *");
System.out.println("\n ********************************************************************\n");
}
}

You are appending to the same string that you are iterating through. Instead, just make your sentence an empty StringBuilder. Then you can append to that while iterating through input. For example:
StringBuilder sentence = new StringBuilder();
//add spaces between the words
for(int i=0; i < input.length(); i++)
{
char letter = input.charAt(i);
if(i != 0 && Character.isUpperCase(letter))
{
sentence.append(' ');
sentence.append(Character.toLowerCase(letter));
}
else
{
sentence.append(letter);
}
}
(Note that I've changed the variable name from index to letter, which is a lot less confusing.)

You have a few different problems here. The main one is that when you call
sentence.setCharAt(index, Character.toLowerCase(index));
you're passing in the actual character in as the first argument, instead of the position. You see, you've just done
index = sentence.charAt(i);
so index is the character itself. Java implicitly converts this character to an integer - but it's not the integer that you want it to be. You probably should have written
sentence.setCharAt(i, Character.toLowerCase(index));
instead.
Also, your sentence.append(' '); will append the space to the end of the StringBuilder, rather than inserting it where you want it to.
And your final sentence.append(index); will duplicate the character. I really don't think you want to do this.

Need help splitting a string into two separate integers for processing

I am working on some data structures in java and I am a little stuck on how to split this string into two integers. Basically the user will enter a string like '1200:10'. I used indexOf to check if there is a : present, but now I need to take the number before the colon and set it to val and set the other number to rad. I think I should be using the substring or parseInt methods, but am unsure. The code below can also be viewed at http://pastebin.com/pJH76QBb
import java.util.Scanner; // Needed for accepting input
public class ProjectOneAndreD
{
public static void main(String[] args)
{
String input1;
char coln = ':';
int val=0, rad=0, answer=0, check1=0;
Scanner keyboard = new Scanner(System.in); //creates new scanner class
do
{
System.out.println("****************************************************");
System.out.println(" This is Project 1. Enjoy! "); //title
System.out.println("****************************************************\n\n");
System.out.println("Enter a number, : and then the radix, followed by the Enter key.");
System.out.println("INPUT EXAMPLE: 160:2 {ENTER} "); //example
System.out.print("INPUT: "); //prompts user input.
input1 = keyboard.nextLine(); //assigns input to string input1
check1=input1.indexOf(coln);
if(check1==-1)
{
System.out.println("I think you forgot the ':'.");
}
else
{
System.out.println("found ':'");
}
}while(check1==-1);
}
}

Substring would work, but I would recommend looking into String.split.
The split command will make an array of Strings, which you can then use parseInt to get the integer value of.
String.split takes a regex string, so you may not want to just throw in any string in it.
Try something like this:
"Your|String".split("\\|");, where | is the character that splits the two portions of the string.
The two backslashes will tell Java you want that exact character, not the regex interpretation of |. This only really matters for some characters, but it's safer.
Source: http://www.rgagnon.com/javadetails/java-0438.html
Hopefully this gets you started.

make this
if(check1==-1)
{
System.out.println("I think you forgot the ':'.");
}
else
{
String numbers [] = input1.split(":"); //if the user enter 1123:2342 this method
//will
// return array of String which contains two elements numbers[0] = "1123" and numbers[1]="2342"
System.out.print("first number = "+ numbers[0]);
System.out.print("Second number = "+ numbers[1]);
}

You knew where : is occurs using indexOf. Let's say string length is n and the : occurred at index i. Then ask for substring(int beginIndex, int endIndex) from 0 to i-1 and i+1 to n-1. Even simpler is to use String::split