Develop Reference

Understanding the method removeChar

At school we were looking at a code for removing a character from a string.
I have a problem understanding the for loop in this code.
What happens if word.charAt(i) is equal to c? If word.charAt(i) is not equal to c the character is printed out. (words.charAt(i) gets printed out)
But if it is equal to c, where in the code does the character get removed?
Thank you in advance for your help. And I'm sorry for my bad English.
This is the code our teacher gave us:
String removeChar(String word, char c) {
String result = "";
for (int i = 0; i<word.length();i++) {
if (word.charAt(i) !=c) {
result += word.charAt(i);
}
}
return result;
}

You can read this code like:
Create an empty String result.
For each letter from word, check if it is not 'c' character. Only if it is not 'c', append this letter to result String (add this letter at the end of result String). If currently checked character is equal to 'c', do nothing.
When loop reaches the end of word, return result String.
By the way, appending String in a loop using += operator is not that efficient like using class StringBuilder and its append() method.

The char is not really removed;
it's simply not append (result += word.charAt(i)) into the string result.
In this way the string that is returned by the method is formed only by the chars that are different from char c.

This code just creates new String object (see variable result). At end of function this new string contains only characters which do not equal to c. Next it string returns as result of function.
Java strings is not mutable, so this is only way to "modify" string - create brand new string.

Character is not actually removed its just been appended to the empty new string(String result = "";) which you have declared above,when word doesn't contain the character 'c', then those characters are getting appended to result, finally you are retrieving that 'Result' string not 'Word',it still containing same value which you have sent.

How to extract words from a string in Java

I've imported a file and turned it into a String called readFile. The file contains two lines:
qwertyuiop00%
qwertyuiop
I have already extracted the "00" from the string using:
String number = readFile.substring(11, 13);
I now want to extract the "ert" and the "uio" in "qwertyuiop"
When I try to use the same method as the first, like so:
String e = readFile.substring(16, 19);
String u = readFile.substring(20, 23);
and try to use:
System.out.println(e + "and" + u);
It says string index out of range.
How do I go about this?
Is it because the next two words I want to extract from the string are on the second line?
If so, how do I extract only the second line?
I want to keep it basic, thanks.
UPDATE:
it turns out only the first line of the file is being read, does anyone know how to make it so it reads both lines?

If you count the total number of characters for each string, they are more than the indexes your entering.
qwertyuiop00% is 13 characters. Call .length() method on the string to verify the length is the one you expect.
I would debug with adding the following before:
System.out.println(readFile);
System.out.println(readFile.length());
Note:
qwertyuiop00% qwertyuiop is 24 characters since space counts as a character. Unless ofcourse you don't have the space in which it's 23 characters and your indexes are 0 to 22
Note2:
I asked for the parser code since I suspect your using the usual code which is something like:
while ((line = reader.readLine()) != null)
You need to concatenate those lines into one String (though it's not the best approach).
see: How do I create a Java string from the contents of a file?

First split your string into lines, you could do this using
String[] lines = readFile.split("[\r\n]+");
You may want to read the content directly into a List<String> using Files.#readAllLines instead.
second, do not use hard coded indexes, use String#indexOf to find them out. If a substring does not occur in your original string, then the method retunrs -1, always check for that value and call substring only when the return value is not -1 (0 or greater).
if(lines.length > 1) {
int startIndex = lines[1].indexOf("ert");
if(startIndex != -1) {
// do what you want
}
}
Btw, there is no point in extracting already known substring from a string
System.out.println(e + "and" + u);
is equivalent to
System.out.println("ertanduio");
Knowing the start and end position of a fixed substring makes only sence if you want to do something with rest of original string, for example removing the substrings.

You may give this a try:-
Scanner sc=new Scanner(new FileReader(new File(The file path for readFile.txt)));
String st="";
while(sc.hasNext()){
st=sc.next();
}
System.out.println(st.substring(2,5)+" "+"and"+" "+st.substring(6,9));
Check out if it works.

Making only the first letter of a word uppercase

I have a method that converts all the first letters of the words in a sentence into uppercase.
public static String toTitleCase(String s)
{
String result = "";
String[] words = s.split(" ");
for (int i = 0; i < words.length; i++)
{
result += words[i].replace(words[i].charAt(0)+"", Character.toUpperCase(words[i].charAt(0))+"") + " ";
}
return result;
}
The problem is that the method converts each other letter in a word that is the same letter as the first to uppercase. For example, the string title comes out as TiTle
For the input this is a title this becomes the output This Is A TiTle
I've tried lots of things. A nested loop that checks every letter in each word, and if there is a recurrence, the second is ignored. I used counters, booleans, etc. Nothing works and I keep getting the same result.
What can I do? I only want the first letter in upper case.

Instead of using the replace() method, try replaceFirst().
result += words[i].replaceFirst(words[i].charAt(0)+"", Character.toUpperCase(words[i].charAt(0))+"") + " ";
Will output:
This Is A Title

The problem is that you are using replace method which replaces all occurrences of described character. To solve this problem you can either
use replaceFirst instead
take first letter,
create its uppercase version
concatenate it with rest of string which can be created with a little help of substring method.
since you are using replace(String, String) which uses regex you can add ^ before character you want to replace like replace("^a","A"). ^ means start of input so it will only replace a that is placed after start of input.
I would probably use second approach.
Also currently in each loop your code creates new StringBuilder with data stored in result, append new word to it, and reassigns result of output from toString().
This is infective approach. Instead you should create StringBuilder before loop that will represent your result and append new words created inside loop to it and after loop ends you can get its String version with toString() method.

Doing some Regex-Magic can simplify your task:
public static void main(String[] args) {
final String test = "this is a Test";
final StringBuffer buffer = new StringBuffer(test);
final Pattern patter = Pattern.compile("\\b(\\p{javaLowerCase})");
final Matcher matcher = patter.matcher(buffer);
while (matcher.find()) {
buffer.replace(matcher.start(), matcher.end(), matcher.group().toUpperCase());
}
System.out.println(buffer);
}
The expression \\b(\\p{javaLowerCase}) matches "The beginning of a word followed by a lower-case letter", while matcher.group() is equal to whats inside the () in the part that matches. Example: Applying on "test" matches on "t", so start is 0, end is 1 and group is "t". This can easily run through even a huge amount of text and replace all those letters that need replacement.
In addition: it is always a good idea to use a StringBuffer (or similar) for String manipulation, because each String in Java is unique. That is if you do something like result += stringPart you actually create a new String (equal to result + stringPart) each time this is called. So if you do this with like 10 parts, you will in the end have at least 10 different Strings in memory, while you only need one, which is the final one.
StringBuffer instead uses something like char[] to ensure that if you change only a single character no extra memory needs to be allocated.
Note that a patter only need to be compiled once, so you can keep that as a class variable somewhere.

why does this for loop wordcount method not work in java

Can anyone let me know why this wordsearch method doesn't work - the returned value of count is 0 everytime I run it.
public int wordcount(){
String spaceString = " ";
int count = 0;
for(int i = 0; i < this.getString().length(); i++){
if (this.getString().substring(i).equals(spaceString)){
count++;
}
}
return count;
}
The value of getString = my search string.
Much appreciated if anyone can help - I'm sure I'm prob doing something dumb.
Dylan

Read the docs:
The substring begins with the character at the specified index and extends to the end of this string.
Your if condition is only true once, if the last character of the string is a space. Perhaps you wanted charAt? (And even this won't properly handle double spaces; splitting on whitespace might be a better option.)

Because substring with only one argument returns the sub string starting from that index till the end of the string. So you're not comparing just one character.
Instead of substring define spaceString as a char, and use charAt(i)

this.getString().substring(i) -> this returns a sub string from the index i to the end of the String
So for example if your string was Test the above would return Test, est, st and finally t
For what you're trying to do there are alternative methods, but you could simple replace
this.getString().substring(i)
with
spaceString.equals(this.getString().charAt(i))
An alternative way of doing what you're trying to do is:
this.getString().split(spaceString)
This would return an array of Strings - the original string broken up by spaces.

Read the documentation of the method you are using:
http://docs.oracle.com/javase/7/docs/api/java/lang/String.html#substring(int)
I.e. the count will be non zero only if you have a space on the end of your string

Using substring as you are will not work. If the value of getString() is "my search string" every iteration through the loop with have substring(i) return:
my search string
y search string
search string
search string
earch string
arch string
rch string
ch string
h string
string
string
tring
ring
ing
ng
g
Notice none of those equals " ".
Try using split.
public int countWords(String s){
return s.split("\\s+").length;
}

Change
if (this.getString().substring(i).equals(spaceString))
to
if (this.getString().charAt(i) == ' ')

this.getString().substring(i) returns a string from the index of (i) to the end of the string.
Example: for i=5, it will return "rown cow" from the string "the brown cow". This functionality isn't what you need.
If you pepper System.out.println() throughout your code (or use the debugger), you will see this.
I think it would be better to use something like String.split() or charAt(i).
By the way, even if you fix your code by counting spaces, it will not return the correct value for these conditions: "my dog" (word count=2) and "cow" (word count=1). There is also a problem if there are more than one space between words. ALso, this will produce a word cound of three:
" the cow ".

How to delete duplicated characters in a string?

Okay, I'm a huge newbie in the world of java and I can't seem to get this program right. I am suppose to delete the duplicated characters in a 2 worded string and printing the non duplicated characters.
for example:I input the words "computer program." the output should be "cute" because these are the only char's that are not repeated.
I made it until here:
public static void main(String[] args) {
System.out.print("Input two words: ");
String str1 = Keyboard.readString();
String words[] = str1.split(" ");
String str2 = words[0] + " ";
String str3 = words[words.length - 1] ;
}
but i don't know how to output the characters. Could someone help me?
I don't know if I should use if, switch, for, do, or do-while...... I'm confused.

what you need is to build up logic for your problem. First break the problem statement and start finding solution for that. Here you go for steps,
Read every character from a string.
Add it to a collection, but before adding that, just check whether it exists.
If it exists just remove it and continue the reading of characteer.
Once you are done with reading the characters, just print the contents of collection to console using System.out.println.
I will recommend you to refer books like "Think like A Programmer". This will help you to get started with logic building.

Just a hint: use a hash map (http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html).

Adding following code after last line of your main program will resolve your issue.
char[] strChars = str2.toCharArray();
String newStr="";
for (char c : strChars) {
String charStr = ""+c;
if(!str3.contains(charStr.toLowerCase()) && !str3.contains(charStr.toUpperCase())){
newStr+=c;
}
}
System.out.println(newStr);
This code loops through all the characters of the first word and check if the second string contains that character (In any form of case Lower or Upper). If it is not containing, adding it to output string and at the end printing it.
Hope this will work in your case.

How about doing it in just 1 line?
str = str.replaceAll("(.)(?=.*\\1)", "");