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How to code this specific for loop in Java?

I have created an average word length checker in Python and I want to convert it into Java.
This is the for loop in Python:
for p in "!£$€%^&*()-_=+`¬¦[]{};:'##~,.<>/?|":
sentence = sentence.replace(p, '')
words = sentence.split()
I want to code this in Java.
Here is what I've tried in Java:
public class AverageWordLength {
public void average_word_length(String sentence){
String characters = "!£$€%^&*()-_=+`¬¦[]{};:'##~,.<>/?|"
for (char p: characters){
}
}
Any hints on how to do this?

String has a split method to split a string with a regular expression
With the stream method the array is converted in a stream.
With the map for each part the length is calculated
And at last the collect returns the average of the length
public class WordLengthChecker {
public static void main(String[] args) {
System.out.println(average_word_length("String_to_split[on(special]characters") );
}
public static double average_word_length(String sentence){
String characters = "[!£$€%^&*()\\-_=+`¬¦\\[\\]{};:'##~,.<>/?|]";
return Arrays.stream(sentence.split(characters))
.map(i -> i.length())
.collect(Collectors.averagingDouble(i -> i));
}
}
.

Regex to validate that every digit is different from each other

I have to validate strings with specific conditions using a regex statement. The condition is that every digit is different from each other. So, 123 works but not 112 or 131.
So, I wrote a statement which filters a string according to the condition and prints true once a string fullfies everything, however it only seems to print "true" altough some strings do not meet the condition.
public class MyClass {
public static void main(String args[]) {
String[] value = {"123","951","121","355","110"};
for (String s : value){
System.out.println("\"" + s + "\"" + " -> " + validate(s));
}
}
public static boolean validate(String s){
return s.matches("([0-9])(?!\1)[0-9](?!\1)[0-9]");
}
}

#Vinz's answer is perfect, but if you insist on using regex, then you can use:
public static boolean validate(String s) {
return s.matches("(?!.*(.).*\\1)[0-9]+");
}

You don't need to use regex for that. You can simply count the number of unique characters in the String and compare it to the length like so:
public static boolean validate(String s) {
return s.chars().distinct().count() == s.length();
}

Java recursive method that removes all instances of a second string in the first string and returns the new first string

I am trying to write a recursive method in Java that accepts two strings and then goes ahead and removes the instances of the second string from the first string (one at a time).
ex. String 1 == Mississippi, String 2 iss
first recursion == Missippi
then the final result should return Mippi
public class RecursionEx {
public static void main(String[] args) {
String str1 = "Mississippi";
String str2 = "iss";
System.out.println(repString(str1, str2));
}
public static String repString(String string1, String string2) {
//base case
if(string1.length()== 0)
return "";
//recursive case
if (string1.substring(0, string2.length()) == string2)
return repString(string1.substring(string2.length()), string2);
else
return repString(string1.substring(1), string2);
}}

Like the comment suggests, you should use equals() when comparing strings in Java, but you can also simplify your life by using the contains and removeFirst method for strings to deal with this recursive task.
I added a print line to the recursive function to show it is removing one instance of string2 at a time from string1.
public class StringRecursion {
public static void main(String[] args) {
String str1 = "Mississippi";
String str2 = "iss";
System.out.println(repString(str1, str2));
}
public static String repString(String string1, String string2) {
if(string1.contains(string2)) {
string1 = string1.replaceFirst(string2, "");
System.out.println("The string is currently: "+ string1);
}
else {
return string1;
}
return repString(string1, string2);
}
}
Output:
The string is currently: Missippi
The string is currently: Mippi
Mippi
Important: One other thing to consider with such an approach is if you want the pattern "iss" formed by an intermediate removal to also be removed. For instance, if you have the word "iissss" and want to remove "iss" it would become "" after running this even though iss does not appear twice in the word initially.
If you want to have the behavior mimic replaceAll function, where we are looking to only get rid of the "iss" patterns in the very first word and not the ones that appear in intermediate steps, I believe the function:
public static String repString(String string1, String string2) {
if(string1.contains(string2)) {
Pattern pattern = Pattern.compile(string2);
long originalCounts = pattern.matcher(string1).results().count();
string1 = string1.replaceFirst(string2, "");
long newCounts = pattern.matcher(string1).results().count();
if(originalCounts == newCounts) {
Matcher matcher = pattern.matcher(string1);
matcher.find();
int startPosition = matcher.end();
//Skip the generated matching pattern that appears in-between.
return string1.substring(0, startPosition) + repString(string1.substring(startPosition), string2);
}
//System.out.println("The string is currently: "+ string1);
}
else {
return string1;
}
return repString(string1, string2);
}
will be sufficient instead.

Regex filename with exactly 2 underscores

I need to match if filenames have exactly 2 underscores and extension 'txt'.
For example:
asdf_assss_eee.txt -> true
asdf_assss_eee_txt -> false
asdf_assss_.txt -> false
private static final String FILENAME_PATTERN = "/^[A-Za-z0-9]+_[A-Za-z0-9]+_[A- Za-z0-9]\\.txt";
does not working.

You just need to add + after the third char class and you must remove the first forward slash.
private static final String FILENAME_PATTERN = "^[A-Za-z0-9]+_[A-Za-z0-9]+_[A-Za-z0-9]+\\.txt$";

You can use a regex like this with insensitive flag:
[a-z\d]+_[a-z\d]+_[a-z\d]+\.txt
Or with inline insensitive flag
(?i)[a-z\d]+_[a-z\d]+_[a-z\d]+\.txt
Working demo
In case you want to shorten it a little, you could do:
([a-z\d]+_){2}[a-z\d]+\.txt

Update
So lets assume you want to at least one or more characters after the second underscore, before the file extension.
Regex is still not "needed" for this. You could split the String by the underscore and you should have 3 elements from the split. If the 3rd element is just ".txt" then it's not valid.
Example:
public static void main(String[] args) throws Exception {
String[] data = new String[] {
"asdf_assss_eee.txt",
"asdf_assss_eee_txt",
"asdf_assss_.txt"
};
for (String d : data) {
System.out.println(validate(d));
}
}
public static boolean validate(String str) {
if (!str.endsWith(".txt")) {
return false;
}
String[] pieces = str.split("_");
return pieces.length == 3 && !pieces[2].equalsIgnoreCase(".txt");
}
Results:
true
false
false
Old Answer
Not sure I understand why your third example is false, but this is something that can easily be done without regex.
Start with checking to see if the String ends with ".txt", then check if it contains only two underscores.
Example:
public static void main(String[] args) throws Exception {
String[] data = new String[] {
"asdf_assss_eee.txt",
"asdf_assss_eee_txt",
"asdf_assss_.txt"
};
for (String d : data) {
System.out.println(validate(d));
}
}
public static boolean validate(String str) {
if (!str.endsWith(".txt")) {
return false;
}
return str.chars().filter(c -> c == '_').count() == 2;
}
Results:
true
false
true

Use this Pattern:
Pattern p = Pattern.compile("_[^_]+_[^_]+\\.txt")
and use .find() instead of .match() in the Matcher:
Matcher m = p.matcher(filename);
if (m.find()) {
// found
}

Find variable ID's in a string with random text

I have something like the following as a String: http://pastebin.com/8QxSC8zJ
What I actually need are the SteamIDs, e.g. "STEAM_0:1:49093894". The part "STEAM_0" is always identical, but the two numbers after that are variable. What would be the best way to retrieve these ID's as a String array?
Update: I looked up regular expressions like Jim Garrison suggested and came up with the following:
String out = //see pastebin
String[] substrings = out.split("\\s+"); //splits at whitespace
for(String a : substrings) {
if(a.matches("STEAM_0.*")) {
System.out.println(a);
//add to string array/list/whatever
}
}
This does indeed print all SteamID's (and I could add them to a String-Array), but how would I do this if there would be no whitespaces in the String?

If you want String array you have to know the length, so as to initialize the array. Let's say it is 3. You can do :
public class Main {
public static void main(String[] args) {
public static void main(String[] args) {
String Str = new String("STEAM_0:1:49093894");
String[] array= new String[2];
array[0]=Str.substring(8,9) ;
array[1]=Str.substring(9);
}
}