Develop Reference

How can I fix my code to find a certain character in an array and make changes to that array

while (scan_file.hasNext()) {
String b = scan_file.nextLine();
// checks if string b contains the tag <h>
if (b.contains("<h>")) {
char arrayString[] = b.toCharArray();
for (int i = 0; i < arrayString.length; i++) {
if (arrayString[i] == '<') {
arrayString[i] = arrayString[i + 2];
}
System.out.print(arrayString[i]);
}
}
}
What I was expecting the program to do was(for now) iterate through the while loop and store each line as string 'b'.
I want to check if that string b contains a certain string like <h> for this example. And I want to convert string b into an array if it contains said string like <h> and iterate through that array to check for '<' and move the array up 2 spaces.
For example, string b had <h>hello, I wanted to eventually print hello because the program would have moved up 2 elements.
I feel like I got the loops and general idea on how I want to tackle the problem.. but when I ran the program, nothing printed so I don't know if I did the loops and if statements correctly.
I really don't know how to word my problem well, so bear with me and I'm sorry in advance.
All feedbacks are greatly appreciated (:

System.out.print(arrayString[i]); just print the ith character of arrayString, it's definitely not what you want.
In fact you don't have to convert a String to char[], String has many utils method can help you with your goal.
I won't give you full code , but I can give you some tips.
You can use String.indexof('<') to find the index of '<'.
You can use String.subString(startIndex) to get the subString start with the specified index.

Suppose your code scan_file.hasNext() and scan_file.nextLine() is work well. You can try code below to remove all from current line:
if (b != null && b.contains("<h>")) {
System.out.println(b.replaceAll("<h>", ""));
}

Reading string from raw txt file

I have a raw txt file with delimiters which i use to split text. To receive text I use scanner:
int textid = getResources().getIdentifier(word, null, this.getPackageName());
Scanner ch = new Scanner(getResources().openRawResource(textid));
Opened file is correct. When I begin receiving information I need to read it until "$" is got.
while (ch.hasNext()) {
str = ch.next();
boolean flag = (str.equals("$"));
while (!(str.equals("$"))) {
str = ch.next();
}
The problem is that when str equals "$" (Checked it through breakpoint) flag equals "false". However, if I initialize String m = "$" and check flag = m.equals("$")flag equals "true". Also tried to use str != "$" but it didn't help.
My guess is that scanner.next() returns another type but it seems to be rather strange.

This might help you.
First next() reads multiple characters until whitespace is found.
Go through every char in str to see if its the '$'. Then when you find it do whatever you wanted to do.
while (ch.hasNext()) {
String str = ch.next();
for(int i = 0; i<str.length(); i++) {
if(str.charAt(i) == '$') {
//do something
}
}
}

When your code reads a "$", it will break the inner loop. When it starts over the outer loop, you're calling ch.next() again, which overwrites the previous "$"in str. This might be the reason why flag is set to false. It would detect the "$" only if it's the first thing in the file.
Also, you might want to check ch.hasNext() in the inner loop again.

How to check if there are double letters in a 4 digit code in Java

The above question might seems vague but it's actually a very simple idea which i can't seem to figure out.
It basically is a 4 digit letter code containing letters from A to F for example: ABDF, BAAF, DBAF etc.
Now I'm trying to do some post input-handling where it must become impossible to enter a letter that is already in the code cause it has to be a unique 4 digit code with no repeating letter. I've been trying to make it work but none of my code seems to work so i'm back to scratch asking you guys for help :)
I hope this is somewhat clear otherwise i'll be happy to clear it up.
Thanks in advance.

Kind of a pseudocode but it would work.
String uniquePass="";
while(uniquePass.length<4){
String userInput=getUserInputChar()
if(uniquePass.contains(userInput))
rejectInputAndNotifyUser
else
uniquePass=uniquePass+userInput
}

public static boolean hasDuplicateChars(String string) {
Set<Character> chars = new HashSet<Character>();
for (char c : string.toCharArray()) {
if (!chars.add(c)) return false;
}
return true;
}
Set is a collection that contains no duplicate elements. We will use add method which returns true if this set did not already contain the specified element.
hasDuplicateChars functions iterates over characters in the input string using toCharArray function and for loop; each character is added to the chars set which is initially empty. If add method returns false it means that we have already encountered same character before. So we return false from our function.
Otherwise input is valid and method returns true.

using this function you'll be able to see if the string contains unique characters
public static boolean checkForUnique(String str){
boolean containsUnique = false;
for(char c : str.toCharArray()){
if(str.indexOf(c) == str.lastIndexOf(c)){
containsUnique = true;
} else {
containsUnique = false;
}
}
return containsUnique;
}
Update:
This will be ran everytime a user enters a character and if it fails, this would mean there is a duplicate. You have the choice of discarding that input or showing an error.

If you're validating the complete input, you can lean on the set semantics, and a few tricks
String s = "ABAF";
int count = new HashSet<>(Arrays.asList(s.split(""))).size();
if (count - 1 == 4) {
System.out.println("All ok");
} else {
System.out.println("Repeated letters");
}
the split("") will split the string to a an array like {"","A", "B", "A", "F"}.
The new HashSet<>(Arrays.asList(s.split(""))) will create a Set with String elements, and as the Set will bounce back the elements already contained, the size of the set for e.g. "AAAF" will be 3 (it'll contain the "", "A" and "F"). This way you can use the size of the set to figure out if all letters of a String are unique
If its while typing you'll than the solution depends on the input method, but you can have something like (pseudo stuff)
if (pass.contains(letter)) {
breakAndNotifyUser();
} else {
pass+=letter;
}

Replacing words in a String java

Say I have a string,
String templatePhrase = "I have a string that needs changing";
I also have a method to replace words in any given String. Here is the method:
public String replace(String templatePhrase, String token, String wordToPut) {
return templatePhrase.replace(token, wordToPut);
}
Now say (for the sake of my actual task) I have all the words in my String str in a List named wordsInHashtags. I want to loop through all the words in wordsInHashtags and replace them with words from another List named replacement using the replace() method. Each time the loop iterates, the modified String should be saved so it will hold its replacement(s) for the next loop.
I will post my code if anyone would like to see it, but I think it would confuse more than help, and all I am interested in is a way to save the modified String for use in the next iteration of the loop.

I was just reading about strings in beginning Java 2 the other day, :"Strings Objects are immutable" Cant be changes basically however StringBuffer Objects were created to deal with such a circumstance as i understand it. You could try:
StringBuffer templatePhrase = "I have a string to be changed";
templatePhrase.replace(token, wordToPut);
String replacedString = (String)templatePhrase;
Line 3 may cause a problem?

public class Rephrase {
public static void main(String[] args) {
/***
Here is some code that might help to change word in string. originally this is a Question from Absolute Java 5th edition. It will change two variable whatever you want but algorithm never change.So the input from keyboard or any other input source.
********/
String sentence = "I hate you";
String replaceWord = " hate";
String replacementWord = "love";
int hateIndex = sentence.indexOf(replaceWord);
String fixed = sentence.substring(0,hateIndex)+" "+replacementWord+sentence.substring(hateIndex+replaceWord.length());
System.out.println(fixed);
}
}

Efficent way to replace underscore with char or string

I have researched this topic for a while, but without much success. I did find the StringBuilder and it works wonders, but that's as far as I got. Here is how I got my hangman program to work like it should:
if(strGuess.equalsIgnoreCase("t")){
mainword.replace(0,1,"T");
gletters.append('T');
}
else if(strGuess.equalsIgnoreCase("e")){
mainword.replace(1,2,"E");
gletters.append('E');
}
else if(strGuess.equalsIgnoreCase("c")){
mainword.replace(2,3,"C");
gletters.append('C');
}
else if(strGuess.equalsIgnoreCase("h")){
mainword.replace(3,4,"H");
gletters.append('H');
}
else if(strGuess.equalsIgnoreCase("n")){
mainword.replace(4,5,"N");
gletters.append('N');
}
else if(strGuess.equalsIgnoreCase("o")){
mainword.replace(5,6,"O");
mainword.replace(7,8,"O");
gletters.append('O');
}
else if(strGuess.equalsIgnoreCase("l")){
mainword.replace(6,7,"L");
gletters.append('L');
}
else if(strGuess.equalsIgnoreCase("g")){
mainword.replace(8,9,"G");
gletters.append('G');
}
else if(strGuess.equalsIgnoreCase("y")){
mainword.replace(9,10,"Y");
gletters.append('Y');
}
else{
JOptionPane.showMessageDialog(null, "Sorry, that wasn't in the word!");
errors++;
gletters.append(strGuess.toUpperCase());
}
SetMain = mainword.toString();
GuessedLetters = gletters.toString();
WordLabel.setText(SetMain);
GuessedLabel.setText(GuessedLetters);
GuessText.setText(null);
GuessText.requestFocusInWindow();
However, I can't do this for EVERY letter for EVERY word, so is there a simple and efficient way to do this? What I want is to have a loop of some sort so that I would only have to use it once for whatever word. So the word could be technology (like it is above) or apple or pickles or christmas or hello or whatever.
I have tried using a for loop, and I feel the answer lies in that. And if someone could explain the charAt() method and how/where to use it, that'd be good. The closest I got to being more efficient is:
for(i = 0; i < GuessWord.length(); i++) {
if (GuessWord.charAt(i) == guess2) {
mainword.replace(i,i,strGuess.toUpperCase());
}
So if you could use that as a basis and go off of it, like fix it? Or tell me something I haven't thought of.

It's a good question. There's clearly repeated code, so how do you replace all that with something reusable. Actually, you can dispense with all of your code.
That whole code block can be replaced by just one line (that works for every word)!
String word = "TECHNOLOGY"; // This is the word the user must guess
mainword = word.replaceAll("[^" + gletters + "]", "_");
This uses replaceAll() with a regex that means "any letter not already guessed" and replaces it with a underscore character "_". Note that Strings are immutable, and the replaceAll() method returns the modified String - it doesn't modify the String called on.
Here's some test code to show it in action:
public static void main(String[] args) {
String word = "TECHNOLOGY"; // what the user must guess
StringBuilder gletters = new StringBuilder("GOTCHA"); // letters guessed
String mainword = word.replaceAll("[^" + gletters + "]", "_");
System.out.println(mainword);
}
Output:
T_CH_O_OG_