Develop Reference

split a string when there is a change in character without a regular expression

There is a way to split a string into repeating characters using a regex function but I want to do it without using it.
for example, given a string like: "EE B" my output will be an array of strings e.g
{"EE", " ", "B"}
my approach is:
given a string I will first find the number of unique characters in a string so I know the size of the array. Then I will change the string to an array of characters. Then I will check if the next character is the same or not. if it is the same then append them together if not begin a new string.
my code so far..
String myinput = "EE B";
char[] cinput = new char[myinput.length()];
cinput = myinput.toCharArray(); //turn string to array of characters
int uniquecha = myinput.length();
for (int i = 0; i < cinput.length; i++) {
if (i != myinput.indexOf(cinput[i])) {
uniquecha--;
} //this should give me the number of unique characters
String[] returninput = new String[uniquecha];
Arrays.fill(returninput, "");
for (int i = 0; i < uniquecha; i++) {
returninput[i] = "" + myinput.charAt(i);
for (int j = 0; j < myinput.length - 1; j++) {
if (myinput.charAt(j) == myinput.charAt(j + 1)) {
returninput[j] += myinput.charAt(j + 1);
} else {
break;
}
}
} return returninput;
but there is something wrong with the second part as I cant figure out why it is not beginning a new string when the character changes.

You question says that you don't want to use regex, but I see no reason for that requirement, other than this is maybe homework. If you are open to using regex here, then there is a one line solution which splits your input string on the following pattern:
(?<=\S)(?=\s)|(?<=\s)(?=\S)
This pattern uses lookarounds to split whenever what precedes is a non whitespace character and what proceeds is a whitespace character, or vice-versa.
String input = "EE B";
String[] parts = input.split("(?<=\\S)(?=\\s)|(?<=\\s)(?=\\S)");
System.out.println(Arrays.toString(parts));
[EE, , B]
^^ a single space character in the middle
Demo

If I understood correctly, you want to split the characters in a string so that similar-consecutive characters stay together. If that's the case, here is how I would do it:
public static ArrayList<String> splitString(String str)
{
ArrayList<String> output = new ArrayList<>();
String combo = "";
//iterates through all the characters in the input
for(char c: str.toCharArray()) {
//check if the current char is equal to the last added char
if(combo.length() > 0 && c != combo.charAt(combo.length() - 1)) {
output.add(combo);
combo = "";
}
combo += c;
}
output.add(combo); //adds the last character
return output;
}
Note that instead of using an array (has a fixed size) to store the output, I used an ArrayList, which has a variable size. Also, instead of checking the next character for equality with the current one, I preferred to use the last character for that. The variable combo is used to temporarily store the characters before they go to output.
Now, here is one way to print the result following your guidelines:
public static void main(String[] args)
{
String input = "EEEE BCD DdA";
ArrayList<String> output = splitString(input);
System.out.print("[");
for(int i = 0; i < output.size(); i++) {
System.out.print("\"" + output.get(i) + "\"");
if(i != output.size()-1)
System.out.print(", ");
}
System.out.println("]");
}
The output when running the above code will be:
["EEEE", " ", "B", "C", "D", " ", "D", "d", "A"]

How to reverse a String after a comma and then print the 1st half of the String Java

For example String grdwe,erwd becomes dwregrdwe
I have most of the code I just have trouble accessing all of ch1 and ch2 in my code after my for loop in my method I think I have to add all the elements to ch1 and ch2 into two separate arrays of characters but I wouldn't know what to initially initialize the array to it only reads 1 element I want to access all elements and then concat them. I'm stumped.
And I'd prefer to avoid Stringbuilder if possible
public class reverseStringAfterAComma{
public void reverseMethod(String word){
char ch1 = ' ';
char ch2 = ' ';
for(int a=0; a<word.length(); a++)
{
if(word.charAt(a)==',')
{
for(int i=word.length()-1; i>a; i--)
{
ch1 = word.charAt(i);
System.out.print(ch1);
}
for (int j=0; j<a; j++)
{
ch2 = word.charAt(j);
System.out.print(ch2);
}
}
}
//System.out.print("\n"+ch1);
//System.out.print("\n"+ch2);
}
public static void main(String []args){
reverseStringAfterAComma rsac = new reverseStringAfterAComma();
String str="grdwe,erwd";
rsac.reverseMethod(str);
}
}

You can use string builder as described here:
First split the string using:
String[] splitString = yourString.split(",");
Then reverse the second part of the string using this:
splitString[1] = new StringBuilder(splitString[1]).reverse().toString();
then append the two sections like so:
String final = splitString[1] + splitString[0];
And if you want to print it just do:
System.out.print(final);
The final code would be:
String[] splitString = yourString.split(",");
splitString[1] = new StringBuilder(splitString[1]).reverse().toString();
String final = splitString[1] + splitString[0];
System.out.print(final);
Then, since you are using stringbuilder all you need to do extra, is import it by putting this at the top of your code:
import java.lang.StringBuilder;

It appears you currently have working code, but are looking to print/save the value outside of the for loops. Just set a variable before you enter the loops, and concatenate the chars in each loop:
String result = "";
for (int a = 0; a < word.length(); a++) {
if (word.charAt(a) == ',') {
for (int i = word.length() - 1; i > a; i--) {
ch1 = word.charAt(i);
result += ch1;
}
for (int j = 0; j < a; j++) {
ch2 = word.charAt(j);
result += ch2;
}
}
}
System.out.println(result);
Demo

Let propose a solution that doesn't use a StringBuilder
You should knoz there is no correct reason not to use that class since this is well tested
The first step would be to split your String on the first comma found (I assumed, in case there is more than one, that the rest are part of the text to reverse). To do that, we can you String.split(String regex, int limit).
The limit is define like this
If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n and the array's last entry will contain all input beyond the last matched delimiter.
If n is non-positive then the pattern will be applied as many times as possible and the array can have any length.
If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.
Example :
"foobar".split(",", 2) // {"foobar"}
"foo,bar".split(",", 2) // {"foo", "bar"}
"foo,bar,far".split(",", 2) // {"foo", "bar,far"}
So this could be used at our advantage here :
String text = "Jake, ma I ,dlrow olleh";
String[] splittedText = text.split( ",", 2 ); //will give a maximum of a 2 length array
Know, we just need to reverse the second array if it exists, using the simplest algorithm.
String result;
if ( splittedText.length == 2 ) { //A comma was found
char[] toReverse = splittedText[1].toCharArray(); //get the char array to revese
int start = 0;
int end = toReverse.length - 1;
while ( start < end ) { //iterate until needed
char tmp = toReverse[start];
toReverse[start] = toReverse[end];
toReverse[end] = tmp;
start++; //step forward
end--; //step back
}
result = new String( toReverse ) + splittedText[0];
}
This was the part that should be done with a StringBuilder using
if ( splittedText.length == 2 ){
result = new StringBuilder(splittedText[1]).reverse().toString() + splittedText[0];
}
And if there is only one cell, the result is the same as the original text
else { //No comma found, just take the original text
result = text;
}
Then we just need to print the result
System.out.println( result );
hello world, I am Jake

Divide string into several substrings

I have a strings that contain only digits. String itself would look like this "0011112222111000" or "1111111000". I'd like to know how can I get an array of substrings which will consist of strings with only one digit.
For example, if I have "00011111122233322211111111110000000" string, I 'd like it to be in string array(string[]) which contains ["000","111111","222","333","222","1111111111","0000000"].
This is what I've tried
for (int i = (innerHierarchy.length()-1); i >= 1; i--) {
Log.e("Point_1", "innerHierarchy " + innerHierarchy.charAt(i));
c = Character.toChars(48 + max);
Log.e("Point_1", "c " + c[0]);
if (innerHierarchy.charAt(i) < c[0] && innerHierarchy.charAt(i - 1) == c[0]) {
Log.e("Point_1", "Start " + string.charAt(i));
o = i;
} else if (innerHierarchy.charAt(i) == c[0] && innerHierarchy.charAt(i - 1) < c[0]) {
Log.e("Point_1", "End " + string.charAt(i));
o1 = i;
string[j] = string.substring(o1,o);
j=j+1;
}
}
But this code won't work if string looks like this "111111000"
Thank you.

I have "00011111122233322211111111110000000" string, I 'd like it to
be in string array(string[]) which contains
["000","111111","222","333","222","1111111111","0000000"]
One approach I can think of right now (O(n)) (might not be the most efficient but would solve your problem) would be traversing the string of numbers i.e. ("00011111122233322211111111110000000" in your case )
and if char at that position under consideration is not same as char at previous position then making string till that part as one string and continuing.
(approach)
considering str= "00011111122233322211111111110000000"
//starting from position 1 (ie from 2nd char which is '0')
//which is same as prev character ( i.e 1st char which is '0')
// continue in traversal
// now char at pos 2 which is again '0'
// keep traversing
// but then char at position 3 is 1
// so stop here and
//make substring till here-1 as one string
//so "000" came as one string
//continue in same manner.
code
import java.util.*;
public class A {
public static void main(String []args){
String str = "00011111122233322211111111110000000";
str+='-'; //appended '-' to get last 0000000 as well into answer
//otherwise it misses last string which i guess was your problem
String one_element ="";
int start=0;
for(int i=1;i<str.length();i++){
if(str.charAt(i)== str.charAt(i-1) )
{
}
else{
one_element = str.substring(start,i);
start = i;
System.out.println(one_element);//add one_element into ArrayList if required.
}
}
}
}
I have printed each element here as string , if you need an array of all those you can simply use an array_list and keep adding one_element in array_list instead of printing.

Copy the first N words in a string in java

I want to select the first N words of a text string.
I have tried split() and substring() to no avail.
What I want is to select the first 3 words of the following prayer and copy them to another variable.
For example if I have a string:
String greeting = "Hello this is just an example"
I want to get into the variable Z the first 3 words so that
Z = "Hello this is"

String myString = "Copying first N numbers of words to a string";
String [] arr = myString.split("\\s+");
//Splits words & assign to the arr[] ex : arr[0] -> Copying ,arr[1] -> first
int N=3; // NUMBER OF WORDS THAT YOU NEED
String nWords="";
// concatenating number of words that you required
for(int i=0; i<N ; i++){
nWords = nWords + " " + arr[i] ;
}
System.out.println(nWords);
NOTE : Here .split() function returns an array of strings computed by splitting a given string around matches of the given regular expression
so if i write the code like follows
String myString = "1234M567M98723651";
String[] arr = myString.split("M"); //idea : split the words if 'M' presents
then answers will be : 1234 and 567 where stored into an array.
This is doing by storing the split values into the given array. first split value store to arr[0], second goes to arr[1].
Later part of the code is for concatenating the required number of split words
Hope that you can get an idea from this!!!
Thank you!

public String getFirstNStrings(String str, int n) {
String[] sArr = str.split(" ");
String firstStrs = "";
for(int i = 0; i < n; i++)
firstStrs += sArr[i] + " ";
return firstStrs.trim();
}
Now getFirstNStrings("Hello this is just an example", 3); will output:
Hello this is

You could try something like:
String greeting = "Hello this is just an example";
int end = 0;
for (int i=0; i<3; i++) {
end = greeting.indexOf(' ', end) + 1;
}
String Z = greeting.substring(0, end - 1);
N.B. This assumes there are at least three space characters in your source string. Any less and this code will probably fail.

Add this in a utility class, such as Util.java
public static String getFirstNWords(String s, int n) {
if (s == null) return null;
String [] sArr = s.split("\\s+");
if (n >= sArr.length)
return s;
String firstN = "";
for (int i=0; i<n-1; i++) {
firstN += sArr[i] + " ";
}
firstN += sArr[n-1];
return firstN;
}
Usage:
Util.getFirstNWords("This will give you the first N words", 3);
---->
"This will give"

If you use Apache Commons Lang3, you can make it a little shorter like this:
public String firstNWords(String input, int numOfWords) {
String[] tokens = input.split(" ");
tokens = ArrayUtils.subarray(tokens, 0, numOfWords);
return StringUtils.join(tokens, ' ');
}

Most of the answers posted already use regular expressions which can become an overhead if we have to process a large number of strings. Even str.split(" ") uses regular expression operations internally. dave's answer is perhaps the mos efficient, but it does not handle correctly strings that have multiple spaces occurring together, beside assuming that regular space is the only word separator and that the input string has 3 or more words (an assumption he has already called out). If using Apache Commons in an option, then I would use the following code as it is not only concise and avoids using regular expression even internally but also handled gracefully input strings that have less than 3 words:
/* Splits by whitespace characters. All characters after the 3rd whitespace,
* if present in the input string, go into the 4th "word", which could really
* be a concanetation of multiple words. For the example in the question, the
* 4th "word" in the result array would be "just an example". Invoking the
* utility method with max-splits specified is slightly more efficient as it
* avoids the need to look for and split by space after the first 3 words have
* been extracted
*/
String[] words = StringUtils.split(greeting, null, 4);
String Z = StringUtils.join((String[]) ArrayUtils.subarray(words, 0, 3), ' ');

Ascending ArrayList is adding element in wrong order

I have a list that is comparing the column elements of an ArrayList (essentially, the string word of an ArrayList that contains string lines).
I was able to read the column part correctly, but there's an error for my insertion method (which I'm doing recursively).
For instance, when it finds a word that is smaller than the previous word, instead of inserting it before the bigger word, it inserts it at the beginning of the ArrayList. I'm not exactly sure why this is, as I seem to be following the steps for insertion exactly what my notes say. Can anyone see why this is happening?
//line is just a string separated by commas
private void insertSorted(String line){
//memFile is the ArrayList
if(memFile.isEmpty()){
memFile.add(0,line);
}
else{
for(int i = memFile.size() - 1; i >=0 ; i--){
int index = i;
String lineList = memFile.get(i);
String[] tokens = line.trim().split(",");
String lineList = memFile.get(i);
String[] tokens1 = lineList.trim().split(",");
//column is the part I want to compare of the tokenized string
while(index >= 0){
if((tokens[column]).compareTo(tokens1[column]) < 0)
index--;
}
break;
}
memFile.add(index+1,line);
System.out.println("memFile is " + memFile);
}//for
}//else
}//insertSorted
It's printing out:
3
1
2
2
4
1
as
1
2
2
3
1
4
Edit:
Say I had an ArrayList memfile, and it contained the strings:
" 1,DOG,Airplane"
" 3,HAT,Basket"
And I wanted to sort the third variables by alphabetically order. Then I would tokenize the string, and from the main method, I would call 2 (column is an instance variable I declared making this class). So, then it would search for tokens[col], or, equivalently, tokens[2].

You have a logic mistake in your method, what you are doing is comparing the line with the last value of the memFile instead of comparing the current index line of the memFile when reducing the index
Here i modified the method according to your required logic.
private void insertSorted(String line) {
// memFile is the ArrayList
if (memFile.isEmpty()) {
memFile.add(0, line);
} else {
int index = memFile.size() - 1;
String[] tokens = line.trim().split(",");
// column is the part I want to compare of the tokenized string
while (index >= 0) {
String lineList = memFile.get(index);
String[] tokens1 = lineList.trim().split(",");
if ((tokens1[column]).compareTo(tokens[column]) > 0) {
index--;
} else {
break;
}
}
memFile.add(index + 1, line);
System.out.println("memFile is " + memFile);
}
}
Hope it helps you