I am trying to replace even incidences in a string with their ASCII value. I'm using the StringBuilder replace method, starting at the index per iteration, ending at the same index, and replacing the value with the ASCII value. For some reason the replace method is not replacing the element at the index with the ASCII value.
sb is my StringBuilder holding the string; result is my desired returned string.
for (int i =0; i < sb.length(); i=i+2) {
char c = sb.charAt(i);
int n = c;
String a = String.valueOf(n);
sb.replace(sb.charAt(i), sb.charAt(i), a);
result = sb.toString();
}
Some things I will correct, but #Nikolai Dmitriev already pointed some of them out.
The n is needed, even though #Nikolai Dmitriev said it's not. Since you want to replace it with its ASCII value. However, you can shorten it to String a = String.valueOf((int) c); or even get rid of the c and just straight up use `String a = String.valueOf((int) sb.charAt(i));
You are using sb.replace(char start, char end, String str); while the function should accept sb.replace(int start, int end, String str);. To correct this, just use sb.replace(i, i + 1, a);. Notice that you use end = i + 1 because the StringBuilder replace function end value is exclusive (not including).
Initialize result at the end. The variable has a scope of inside the for loop if you do it inside, and since you want to return it, you would want to initialized it after you finish replacing all even-indices.
Related
I'm trying to search and reveal unknown characters in a string. Both strings are of length 12.
Example:
String s1 = "1x11222xx333";
String s2 = "111122223333"
The program should check for all unknowns in s1 represented by x|X and get the relevant chars in s2 and replace the x|X by the relevant char.
So far my code has replaced only the first x|X with the relevant char from s2 but printed duplicates for the rest of the unknowns with the char for the first x|X.
Here is my code:
String VoucherNumber = "1111x22xx333";
String VoucherRecord = "111122223333";
String testVoucher = null;
char x = 'x'|'X';
System.out.println(VoucherNumber); // including unknowns
//find x|X in the string VoucherNumber
for(int i = 0; i < VoucherNumber.length(); i++){
if (VoucherNumber.charAt(i) == x){
testVoucher = VoucherNumber.replace(VoucherNumber.charAt(i), VoucherRecord.charAt(i));
}
}
System.out.println(testVoucher); //after replacing unknowns
}
}
I am always a fan of using StringBuilders, so here's a solution using that:
private static String replaceUnknownChars(String strWithUnknownChars, String fullStr) {
StringBuilder sb = new StringBuilder(strWithUnknownChars);
while ((int index = Math.max(sb.toString().indexOf('x'), sb.toString().indexOf('X'))) != -1) {
sb.setCharAt(index, fullStr.charAt(index));
}
return sb.toString();
}
It's quite straightforward. You create a new string builder. While a x or X can still be found in the string builder (indexOf('X') != -1), get the index and setCharAt.
Your are using String.replace(char, char) the wrong way, the doc says
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
So you if you have more than one character, this will replace every one with the same value.
You need to "change" only the character at a specific spot, for this, the easiest is to use the char array that you can get with String.toCharArray, from this, this is you can use the same logic.
Of course, you can use String.indexOf to find the index of a specific character
Note : char c = 'x'|'X'; will not give you the expected result. This will do a binary operation giving a value that is not the one you want.
The OR will return 1 if one of the bit is 1.
0111 1000 (x)
0101 1000 (X)
OR
0111 1000 (x)
But the result will be an integer (every numeric operation return at minimum an integer, you can find more information about that)
You have two solution here, you either use two variable (or an array) or if you can, you use String.toLowerCase an use only char c = 'x'
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I am looking to insert a single letter one by one into every possible index of a string.
For example the string ry
Would go "ary" "bry" "cry" ... "zry" ... "ray" "rby" .... "rzy" ... "rya" "ryb"
I am not sure how to begin, any help?
Try this
System.out.println("originaltext".replaceAll(".{1}","$0ry"));
The above is using the String replaceAll(String regex, String replacement) method - "Replaces each substring of this string that matches the given regular expression with the given replacement."
".{1}" - The regular expression used to find exactly one occurrence({1}) of any character(.)
"$0ry" - The replacement string with "$0" for the matched value followed by the required characters(ry).
This is repeated for all matches!
Example Code
String originalString = /* your original string */;
char[] characters = /* array of characters you want to insert */;
Vector<String> newStrings = new Vector<>();
String newString;
for (int idx = 0; idx < originalString.length() + 1; ++idx) {
for (char ch : characters) {
newString = originalString.substring(0, idx)
+ ch
+ originalString.substring(idx, originalString.length());
newStrings.add(newString);
}
}
Explanation
Processing all cases:
In order to insert every single letter into an index in a string, you need a loop to iterate through every letter.
In order to insert a letter into every index in a string, you need a loop to iterate through every index in the string.
To do both at once, you should nest one loop inside the other. That way, every combination of an index and a character will be processed. In the problem you presented, it does not matter which loop goes inside the other--it will work either way.
(you actually have to iterate through every index in the string +1... I explain why below)
Forming the new string:
First, it is important to note the following:
What you want to do is not "insert a character into an index" but rather "insert a character between two indices". The distinction is important because you do not want to replace the previous character at that index, but rather move all characters starting at that index to the right by one index in order to make room for a new character "at that index."
This is why you must iterate through every index of the original string plus one. Because once you "insert" the character, the length of the new string is actually equal to originalString.length() + 1, i.e. there are n + 1 possible locations where you can "insert" the character.
Considering this, the way you actually form a new string (in the way you want to) is by getting everything to the left of your target index, getting everything to the right of your target index, and then concatenating them with the new character in between, e.g. leftSubstring + newCharacter + rightSubstring.
Now, it might seem that this would not work for the very first and very last index, because the leftSubstring and/or rightSubstring would be an empty string. However, string concatenation still works even with an empty string.
Notes about Example Code
characters can also be any collection that implements iterable. It does not have to be a primitive array.
characters does not have to contain primitive char elements. It may contain any type that can be concatenated with a String.
Note that the substring(int,int) method of String returns the substring including the character at beginIndex but not including the character at endIndex. One implication of this is that endIndex may be equal to string.length() without any problems.
Well you will need a loop for from i = 0 to your string's length
Then another loop for every character you want to insert - so if you want to keep creating new strings with every possible letter from A to Z make a loop from char A = 'a' to 'z' and keep increasing them ++A(this should work in java).
This should give you some ideas.
Supposing, for instance, you want them all in a list, you could do something like that (iterating all places to insert and iterating over all letters):
List<String> insertLetters(String s) {
List<String> list = new ArrayList<String>();
for (int i = 0; i <= s.length(); i++) {
String prefix = s.substring(0, i);
String postfix = s.substring(i, s.length());
for (char letter = 'a'; letter <= 'z'; letter++) {
String newString = prefix + letter + postfix;
list.add(newString);
}
}
return list;
}
String x = "ry";
char[] alphabets = "abcdefghijklmnopqrstuvwxyz".toCharArray();
String[] alphabets2 = new String[alphabets.length];
for (int i=0;i<alphabets.length;i++){
char z = alphabets[i];
alphabets2[i] = z + x;
}
for (String s: alphabets2
) {
System.out.println(s);
}
First of all you would need a Array of alphabet (Easier for you to continue).
I will not give you exact answer, but something to start, so you would learn.
int length = 0;
Arrays here
while(length <= 2) {
think what would be here: hint you put to index (length 0) the all alphabet and move to index 1 and then 2
}
So this is my code in Java (for returning two halves of a string - one is the odd half, starting with the index 0, or the first character, and the second half, starting with the index 1, or the second character):
public class StringTest{
public String halfOfString(String message, int start){
int length = message.length();
StringBuilder output = new StringBuilder(length);
char ch;
int i;
if((start==0)||(start==1)){
for(i=start; i<message.length(); i=i+2){
ch = message.charAt(i);
output.setCharAt(i,ch); // error occurs here
}
}
return output.toString();
}
public void testFunction(){
String s = "My name is Sid";
String first = halfOfString(s, 0);
String second = halfOfString(s, 1);
System.out.println("First half is " + first + " and second half is " + second);
}
}
So my problem is - whenever I attempt to run this program on BlueJ IDE, it doesn't, and returns the error in the title, on the line mentioned in the comment.
I have poured over this site for a similar question which may help me with my error, but all I found was a question which suggested a change I have already implemented (in the StringBuilder setCharAt method, the person had reversed the i and ch parameters).
Is it anything to do with the fact that the "output" is declared empty at first, and the setCharAt method can only replace the characters which already exist?
Any help would be greatly appreciated.
Is it anything to do with the fact that the "output" is declared empty at first, and the setCharAt method can only replace the characters which already exist?
Yes, that is exactly why you get this error.
Note that creating a StringBuilder with a specified length, as you are doing:
StringBuilder output = new StringBuilder(length);
does not create a StringBuilder which already has that many characters - it just creates a StringBuilder with that internal buffer size. The StringBuilder itself still contains no characters, so trying to set the first character will result in the exception that you get.
Call append on the StringBuilder to add characters instead of setCharAt.
Is it anything to do with the fact that the "output" is declared empty
at first, and the setCharAt method can only replace the characters
which already exist?
Yes, that's the reason.
The Javadoc of setCharAt is clear on this:
The index argument must be greater than or equal to 0, and less than
the length of this sequence.
Why don't you just use the append method in StringBuilder? It looks to me like, if your code would work, it would leave holes in the StringBuilder since you're only setting every other character and not the ones in between. Using append ensures that there are no holes.
I am trying to place spaces in between a number that has been entered in a textfield. I am using the following code:
for(int i = 0; i <= 2; i++)
{
char cijfer = tf1.getText().charAt(i);
char getal1 = tf1.getText().charAt(0);
char getal2 = tf1.getText().charAt(1);
char getal3 = tf1.getText().charAt(2);
}
String uitvoerGetal = getal1 + " " + getal2 + " " + getal3;
I suppose I don't understand the charAt() function yet, does anyone have a link explaining it in a way so I might be able to make this work too? Thanks in advance!
Example:
public class Test {
public static void main(String args[]) {
String s = "Strings are immutable";
char result = s.charAt(8);
System.out.println(result);
}
}
This produces the following result:
a
In more Detail From java docs
public char charAt(int index)
Returns the char value at the specified index. An index ranges from 0 to length() - 1. The first char value of the sequence is at index 0, the next at index 1, and so on, as for array indexing.
If the char value specified by the index is a surrogate, the surrogate value is returned.
Specified by:
charAt in interface CharSequence
Parameters:
index - the index of the char value.
Returns:
the char value at the specified index of this string. The first char value is at index 0.
Throws:
IndexOutOfBoundsException - if the index argument is negative or not less than the length of this string.
In straight words You can't. You can't add space in int datatype because int is meant to store the integer value only. Change int to String to store the space in between.
Okay, let's see what's wrong with your code...
Your for-loop is 1-based instead of the standard 0-based. That's not good at all.
You're attempting to assign a char to a String (3 times), the first call to charAt is correct, but for some reason you then switch to using a String?
Finally you're attempting to assign a String to an int, which is just completely nonsensical.
You have a number of problems, but well done on an honest attempt.
First up, the indexes in a string are zero-based, so charAt(0) gives you the first character, charAt(1) gives you the second character, and so on.
Secondly, repeating all your calls to charAt three times is probably unnecessary.
Thirdly, you must be careful with your types. The return value from charAt is a char, not a String, so you can't assign it to a String variable. Likewise, on the last line, don't assign a String to an int variable.
Lastly, I don't think you've thought about what happens if the text field doesn't contain enough characters.
Bearing these points in mind, please try again, and ask for further help if you need it.
Try following code
String text = tf1.getText(); // get string from jtextfield
StringBuilder finalString = new StringBuilder();
for(int index = 0; index <text.length(); index++){
finalString.append(text.charAt(index) + " "); // add spaces
}
tf1.setText(finalString.toString().trim()) // set string to jtextfield
In Java,
I need to read lines of text from a file and then reverse each line, writing the reversed version into another file. I know how to read from one file and write to another. What I don't know how to do is manipulate the text so that "This is line 1" would be written into the second file as "1 enil si sihT"
since these are homeworks you are probably interested in your own implementation of reverse method.
The naive version visits the string backwards (from the last index to the index 0) while copying it in a StringBuilder:
public String reverse(String s) {
StringBuilder sb = new StringBuilder();
for (int i = s.length() - 1; i >= 0; i--) {
sb.append(s.charAt(i));
}
return sb.toString();
}
for example the String "hello":
H e l l o
0 1 2 3 4 // indexes for charAt()
the method start by the index 4 ('o') then the index 3 ('l') ... until 0 ('H').
StringBuilder buffer = new StringBuilder(theString);
return buffer.reverse().toString();
If this is homework, it would be better for you to understand how are data stored into the string it self.
A string may be represented as an array of characters
String line = // read line ....;
char [] data = line.toCharArray();
To reverse an array you have to swap the positions of the elements. The first in the last, the last in the first and so on.
int l = data.length;
char temp;
temp = data[0]; // put the first element in "temp" to avoid losing it.
data[0] = data[l - 1]; // put the last value in the first;
data[l - 1] = temp; // and the first in the last.
Continue with the rest of the elements ( hint use a loop ) in the array and then create a new String with the result:
String modifiedString = new String( data ); // where data is the reversed array.
If is not ( and you really just need to have the work done ) use:
StringBuilder.reverse()
Good luck.
String reversed = new StringBuilder(textLine).reverse().toString();
The provided answers all suggest using an already existing method, which is sound advice and usually more effective than writing your own.
Depending on the assignment, however, your teacher might expect you to write a method of your own. If that is the case, try using a for loop to walk through the string character by character, only instead of counting from zero and up, start counting from the last character index and down to zero, consecutively building the reversed string.
While we're feeding horrible, finished answers to the poor student, we might as well whet his appetite for the bizarre. If strings were guaranteed to be reasonably short and CPU time was no object, this is what I'd code:
public static String reverse(String str) {
if (str.length() == 0) return "";
else return reverse(str.substring(1)) + str.charAt(0);
}
(OK, I admit it: my current favorite language is Clojure, a Lisp!)
BONUS HOMEWORK: Figure out if, how and why this works!
java.lang.StringBuffer has a reverse method.