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Replacing substrings in String

I am 16 and trying to learn Java, I have a paper that my uncle gave me that has things to do in Java. One of these things is too write and execute a program that will accept an extended message as a string such as
Each time she saw the painting, she was happy
and replace the word she with the word he.
Each time he saw the painting, he was happy.
This part is simple, but he wants me to be able to take any form of she and replace it we he like (she to he, She to He, she? to he?, she. to he., she' to he' and so on). Can someone help me make a program to accomplish this.
I have this
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Write Sentence");
String original = keyboard.nextLine();
String changeWord = "he";
String modified = original.replaceAll("she", changeWord);
System.out.println(modified);
}
If this isn't the right site to find answers like this, can you redirect me to a site that answers such questions?

The best way to do this is with regular expressions (regex). Regex allow you to match patterns or classes of words so you can deal with general cases. Consider the cases you have already listed:
(she to he, She to He, she? to he?, she. to he., she' to he' and so on)
What is common between these cases? Can you think of some general rule(s) that would apply to all such transformations?
But also consider some cases you haven't listed: for example, as you've written it now, your code will change the word "ashes" to "ahes" because "ashes" contains "she." A properly written regex expression allows you to avoid this.
Before delving into regex, try and express, in plain English, a rule or set of rules for what you want to replace and what it should be replaced with.
Then, learn some regex and attempt to apply those rules.
Lastly, try and write some tests (i.e. using JUnit) for various cases so you can see which cases your code is working for and which cases it isn't working for.
Once you have done this, if something still doesn't work, feel free to post a new question here showing us your code and explaining what doesn't work. We'll be happy to help.

I would recommend this regular expression to solve this. It seems you have to search and replace separately the uppercase S and the lowercase s
String modified = original
.replaceAll("(she)(\\W)", "he$2")
.replaceAll("(She)(\\W)", "He$2");
Explanation :
The pattern (she) will match the word she and store it as the first captured group of characters
The pattern (\\W) will match one non alphabetic character (e.g. ', .) and store it as the second captured group of characters
Both of these patterns must match consecutive parts of the input string for replaceAll to replace something.
"he$2" put in the resulting string the word he followed by the second captured group of characters (in our case the group has only one character)
The above means that the regular expression will match a pattern like She'll and replace with He'll, but it will not match a pattern like Sherlock because here She is followed by an alphabetic character r

How to extract substrings from a string in java

I am not so confident in Java so I need some help to extract multiple substrings from a string.string is as given below.
I have a text file with possibly thousands of similar POS-tagged lines that I need to extract the original text from that.I have tried using tokenizer but didn't really get the result I wanted.I tried using Pattern Matcher and I am having problems with the regex.
String="I_PRP recently_RB purchased_VBD this_DT camera_NN";
I want to get the output= I recently purchased this camera.
I use
Regex: [\/](.*?)\s\b
But its not working.Please help me.

try
String s= "I_PRP recently_RB purchased_VBD this_DT camera_NN";
s = s.replaceAll("_\\w+(?=(\\s|$))", "");
System.out.println(s);
prints
I recently purchased this camera

It seems that you are attaching a tag to indicate the word type (e.g. noun, verb or pronoun) if this suffix will be always capital letters, it is more safe to use the following regex in your replaceAll
s = s.replaceAll("_[A-Z]+(?=(\\s|$))", "");

select a word from a section of string?

I'm trying to find out if there are any methods in Java which would me achieve the following.
I want to pass a method a parameter like below
"(hi|hello) my name is (Bob|Robert). Today is a (good|great|wonderful) day."
I want the method to select one of the words inside the parenthesis separated by '|' and return the full string with one of the words randomly selected. Does Java have any methods for this or would I have to code this myself using character by character checks in loops?

You can parse it by regexes.
The regex would be \(\w+(\|\w+)*\); in the replacement you just split the argument on the '|' and return the random word.
Something like
import java.util.regex.*;
public final class Replacer {
//aText: "(hi|hello) my name is (Bob|Robert). Today is a (good|great|wonderful) day."
//returns: "hello my name is Bob. Today is a wonderful day."
public static String getEditedText(String aText){
StringBuffer result = new StringBuffer();
Matcher matcher = fINITIAL_A.matcher(aText);
while ( matcher.find() ) {
matcher.appendReplacement(result, getReplacement(matcher));
}
matcher.appendTail(result);
return result.toString();
}
private static final Pattern fINITIAL_A = Pattern.compile(
"\\\((\\\w+(\\\|\w+)*)\\\)",
Pattern.CASE_INSENSITIVE
);
//aMatcher.group(1): "hi|hello"
//words: ["hi", "hello"]
//returns: "hello"
private static String getReplacement(Matcher aMatcher){
var words = aMatcher.group(1).split('|');
var index = randomNumber(0, words.length);
return words[index];
}
}
(Note that this code is written just to illustrate an idea and probably won't compile)

May be it helps,
Pass three strings("hi|hello"),(Bob|Robert) and (good|great|wonderful) as arguments to the method.
Inside method split the string into array
by, firststringarray[]=thatstring.split("|"); use this for other two.
and Use this to use random string selection.

As per my knowledge java don't have any method to do it directly.
I have to write code for it or regexe

I don't think Java has anything that will do what you want directly. Personally, instead of doing things based on regexps or characters, I would make a method something like:
String madLib(Set<String> greetings, Set<String> names, Set<String> dispositions)
{
// pick randomly from each of the sets and insert into your background string
}

There is no direct support for this. And you should ideally not try a low level solution.
You should search for 'random sentence generator'. The way you are writing
`(Hi|Hello)`
etc. is called a grammar. You have to write a parser for the grammar. Again there are many solutions for writing parsers. There are standard ways to specify grammar. Look for BNF.
The parser and generator problems have been solved many time over, and the interesting part of your problem will be writing the grammar.

Java does not provide any readymade method for this. You can use either Regex as described by Penartur or create your own java method to split Strings and store random words. StringTokenizer class can help you if following second approach.

Encoding URL strings with regular expression

I'm trying to replace several different characters with different values. For example, if I have: #love hate then I would like to do is get back %23love%20hate
Is it something to do with groups? i tried to understand using groups but i really didn't understand it.

You can try to do this:
String encodedstring = URLEncoder.encode("#love hate","UTF-8");
It will give you the result you want. To revers it you should do this:
String loveHate = URLDecoder.decode(encodedstring);

You don't need RegEx to replace single characters. RegEx is an overkill for such porposes. You can simply use the plain replace method of String class in a loop, for each character that you want to replace.
String output = input.replace("#", "%23");
output = output.replace(" ", "%20");
How many such characters do you want to get replaced?

If you are trying to encode a URL to utf-8 or some encoding using existing classes will be much easier
eg.
commons-httpclient project
URIUtil.encodeWithinQuery(input,"UTF-8");

No, you will need multiple replaces. Another option is to use group to find the next occurrence of one of several strings, inspect what the string is and replace appropriately, perhaps using a map.

i think what you want to achieve is kind of url encoding instead of pure replacement.
see some answers on this thread of SO , especially the one with 7 votes which may be more interesting for you.
HTTP URL Address Encoding in Java

As Mat said, the best way to solve this problem is with URLEncoder. However, if you insist on using regex, then see the sample code in the documentation for java.util.regex.Matcher.appendReplacement:
Pattern p = Pattern.compile("cat");
Matcher m = p.matcher("one cat two cats in the yard");
StringBuffer sb = new StringBuffer();
while (m.find()) {
m.appendReplacement(sb, "dog");
}
m.appendTail(sb);
System.out.println(sb.toString());
Within the loop, you can use m.group() to see what substring matched and then do a custom substitution based on that. This technique can be used for replacing ${variables} by looking them up in a map, etc.

replacing regex in java string

I have this java string:
String bla = "<my:string>invalid_content</my:string>";
How can I replace the "invalid_content" piece?
I know I should use something like this:
bla.replaceAll(regex,"new_content");
in order to have:
"<my:string>new_content</my:string>";
but I can't discover how to create the correct regex
help please :)

You could do something like
String ResultString = subjectString.replaceAll("(<my:string>)(.*)(</my:string>)", "$1whatever$3");

Mark's answer will work, but can be improved with two simple changes:
The central parentheses are redundant if you're not using that group.
Making it non-greedy will help if you have multiple my:string tags to match.
Giving:
String ResultString = SubjectString.replaceAll
( "(<my:string>).*?(</my:string>)" , "$1whatever$2" );
But that's still not how I'd write it - the replacement can be simplified using lookbehind and lookahead, and you can avoid repeating the tag name, like this:
String ResultString = SubjectString.replaceAll
( "(?<=<(my:string)>).*?(?=</\1>)" , "whatever" );
Of course, this latter one may not be as friendly to those who don't yet know regex - it is however more maintainable/flexible, so worth using if you might need to match more than just my:string tags.

See Java regex tutorial and check out character classes and capturing groups.

The PCRE would be:
/invalid_content/
For a simple substitution. What more do you want?

Is invalid_content a fix value? If so you could simply replace that with your new content using:
bla = bla.replaceAll("invalid_content","new_content");