Develop Reference

Parsing String by pattern of substrings

I need to parse a formula and get all the variables that were used. The list of variables is available. For example, the formula looks like this:
String f = "(Min(trees, round(Apples1+Pears1,1)==1&&universe==big)*number";
I know that possible variables are:
String[] vars = {"trees","rivers","Apples1","Pears1","Apricots2","universe","galaxy","big","number"};
I need to get the following array:
String[] varsInF = {"trees", "Apples1","Pears1", "universe", "big","number"};
I believe that split method is good here but can’t figure the regexp required for this.

No need for any regex pattern - just check which item of the supported vars is contained in the given string:
List<String> varsInf = new ArrayList<>();
for(String var : vars)
if(f.contains(var))
varsInf.add(var);
Using Stream<> you can:
String[] varsInf = Arrays.stream(vars).filter(f::contains).toArray(String[]::new);

Assuming "variable" is represented by one alphanumeric character or sequential sequence of multiple such characters, you should split by not-alphanumeric characters, i. e. [^\w]+, then collect result by iteration or filter:
Set<String> varSet = new HashSet<>(Arrays.asList(vars));
List<String> result = new ArrayList<>();
for (String s : f.split("[^\\w]+")) {
if (varSet.contains(s)) {
result.add(s);
}
}

Removing special characters from string

I want to parse this string into a list and return {1.193493, 54.6333, 2.093077, 31.6235, 6.175355, 21.6479}. How do I get rid of the square brackets???? I used a for loop and replace but it doesn't work.
String st = "[[[1.193493,54.6333],[2.093077,31.6235],[6.175355,21.6479]]]"
String[] parsed = st.split(",");
for (String next : parsed) {
next.replace("//[", "").replace("//]", "");
}

replace() works with plain Strings, not regex. Therefore you can simply use:
next.replace("[", "").replace("]", "");
Also notice that you need to assign it to some string variable; assigning it to need won't work (won't modify elements in parsed array).
You should actually remove the braces first and split later, like this:
String[] parsed = st.replace("[", "").replace("]", "").split(",");

You can do it all at one time with this regex:
(?:\D*(\d*\.\d*))+

You can do this with one line:
List<String> list = Arrays.asList(t.replaceAll("\\[", "").replaceAll("\\]", "").split(","));
Full code:
package com.stackoverflow;
import java.util.Arrays;
import java.util.List;
public class Demo
{
public static void main(String[] args)
{
String t = "[[[1.193493,54.6333],[2.093077,31.6235],[6.175355,21.6479]]]";
List<String> list = Arrays.asList(t.replaceAll("\\[", "").replaceAll("\\]", "").split(","));
for(String s : list)
{
System.out.println(s);
}
}
}
Converts string to list of strings and prints it. If you need to convert strings to doubles, use Double.parseDouble(s) in loop.

You could achieve your goal in two steps.
1) Remove all special characters except comma (,)
2) Then split by comma (,)
public static void main(String[] args) {
String st = "[[[1.193493,54.6333],[2.093077,31.6235],[6.175355,21.6479]]]";
String[] parsed = st.replaceAll("[^\\d.,]+", "").split(",");
}
Output:

java arraylist example with no symbol resolved

I'm just unsure why this isn't working.
ArrayList<String> test1 = new ArrayList<String>();
String[] input = new String[]{"biggest", "next", "not"};
test1.add(input);
there's an error in the 3rd line, at add.
My editor just says the symbol cannot be resolved, and just for the test, I typed test1. and ctrl + spaced it to see what it would give me, but no suggestion.
Any help?

by using add you can just add to the list what you defined in your generic, which would be String in your case. This isn´t valid since you try to add an array of String to your list. to achive this you could us the addAll function like this.
ArrayList<String> test1 = new ArrayList<String>();
String[] input = new String[]{"biggest", "next", "not"};
test1.addAll(Arrays.asList(input));

Try This: ( Use Arrays.asList() )
String[] input = new String[]{"biggest", "next", "not"};
ArrayList<String> test1 =new ArrayList (Arrays.asList(input));
System.out.println(test1);
Or u can use this
List<String> test1 =new ArrayList ();
String[] input = new String[]{"biggest", "next", "not"};
Collections.addAll(test1, input);
System.out.println(test1);
Output:
[biggest, next, not]

Your arraylist is of type "String" , and you are trying to add a "String [ ]" object , you can't do that
if your list is like this
ArrayList<String[]> test1 = new ArrayList<String[]>();
that's will work you can add the array input as an object

Place all text in quotes into ArrayList

I'm looking for an easy way to take a string and have all values in quotes placed into an ArrayList
Eg
The "car" was "faster" than the "other"
I would like to have an ArrayList that contains
car, faster, other
I think I might need to use RegEx for this but I'm wondering if there is another simpler way.

Using a regex, it is actually quite easy. Note: this solution supposes that there cannot be nested quotes:
private static final Pattern QUOTED = Pattern.compile("\"([^\"]+)\"");
// ...
public List<String> getQuotedWords(final String input)
{
// Note: Java 7 type inference used; in Java 6, use new ArrayList<String>()
final List<String> ret = new ArrayList<>();
final Matcher m = QUOTED.matcher(input);
while (m.find())
ret.add(m.group(1));
return ret;
}
The regex is:
" # find a quote, followed by
([^"]+) # one or more characters not being a quote, captured, followed by
" # a quote
Of course, since this is in a Java string quotes need to be quoted... Hence the Java string for this regex: "\"([^\"]+)\"".

Use this script to parse the input:
public static void main(String[] args) {
String input = "The \"car\" was \"faster\" than the \"other\"";
List<String> output = new ArrayList<String>();
Pattern pattern = Pattern.compile("\"\\w+\"");
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
output.add(matcher.group().replaceAll("\"",""));
}
}
Output list contains:
[car,faster,other]

You can use Apache common String Utils substringsBetween method
String[] arr = StringUtils.substringsBetween(input, "\"", "\"");
List<String> = new ArrayList<String>(Arrays.asList(arr));

How to convert a String into an ArrayList?

In my String, I can have an arbitrary number of words which are comma separated. I wanted each word added into an ArrayList. E.g.:
String s = "a,b,c,d,e,.........";

Try something like
List<String> myList = new ArrayList<String>(Arrays.asList(s.split(",")));
Arrays.asList documentation
String.split documentation
ArrayList(Collection) constructor documentation
Demo:
String s = "lorem,ipsum,dolor,sit,amet";
List<String> myList = new ArrayList<String>(Arrays.asList(s.split(",")));
System.out.println(myList); // prints [lorem, ipsum, dolor, sit, amet]
This post has been rewritten as an article here.

String s1="[a,b,c,d]";
String replace = s1.replace("[","");
System.out.println(replace);
String replace1 = replace.replace("]","");
System.out.println(replace1);
List<String> myList = new ArrayList<String>(Arrays.asList(replace1.split(",")));
System.out.println(myList.toString());

In Java 9, using List#of, which is an Immutable List Static Factory Methods, become more simpler.
String s = "a,b,c,d,e,.........";
List<String> lst = List.of(s.split(","));

Option1:
List<String> list = Arrays.asList("hello");
Option2:
List<String> list = new ArrayList<String>(Arrays.asList("hello"));
In my opinion, Option1 is better because
we can reduce the number of ArrayList objects being created from 2 to 1. asList method creates and returns an ArrayList Object.
its performance is much better (but it returns a fixed-size list).
Please refer to the documentation here

Easier to understand is like this:
String s = "a,b,c,d,e";
String[] sArr = s.split(",");
List<String> sList = Arrays.asList(sArr);

Ok i'm going to extend on the answers here since a lot of the people who come here want to split the string by a whitespace. This is how it's done:
List<String> List = new ArrayList<String>(Arrays.asList(s.split("\\s+")));

If you are importing or you have an array (of type string) in your code and you have to convert it into arraylist (offcourse string) then use of collections is better. like this:
String array1[] = getIntent().getExtras().getStringArray("key1"); or String array1[] = ... then
List allEds = new ArrayList(); Collections.addAll(allEds, array1);

You could use:
List<String> tokens = Arrays.stream(s.split("\\s+")).collect(Collectors.toList());
You should ask yourself if you really need the ArrayList in the first place. Very often, you're going to filter the list based on additional criteria, for which a Stream is perfect. You may want a set; you may want to filter them by means of another regular expression, etc. Java 8 provides this very useful extension, by the way, which will work on any CharSequence: https://docs.oracle.com/javase/8/docs/api/java/util/regex/Pattern.html#splitAsStream-java.lang.CharSequence-. Since you don't need the array at all, avoid creating it thus:
// This will presumably be a static final field somewhere.
Pattern splitter = Pattern.compile("\\s+");
// ...
String untokenized = reader.readLine();
Stream<String> tokens = splitter.splitAsStream(untokenized);

If you want to convert a string into a ArrayList try this:
public ArrayList<Character> convertStringToArraylist(String str) {
ArrayList<Character> charList = new ArrayList<Character>();
for(int i = 0; i<str.length();i++){
charList.add(str.charAt(i));
}
return charList;
}
But i see a string array in your example, so if you wanted to convert a string array into ArrayList use this:
public static ArrayList<String> convertStringArrayToArraylist(String[] strArr){
ArrayList<String> stringList = new ArrayList<String>();
for (String s : strArr) {
stringList.add(s);
}
return stringList;
}

Let's take a question : Reverse a String. I shall do this using stream().collect(). But first I shall change the string into an ArrayList .
public class StringReverse1 {
public static void main(String[] args) {
String a = "Gini Gina Proti";
List<String> list = new ArrayList<String>(Arrays.asList(a.split("")));
list.stream()
.collect(Collectors.toCollection( LinkedList :: new ))
.descendingIterator()
.forEachRemaining(System.out::println);
}}
/*
The output :
i
t
o
r
P
a
n
i
G
i
n
i
G
*/

This is using Gson in Kotlin
val listString = "[uno,dos,tres,cuatro,cinco]"
val gson = Gson()
val lista = gson.fromJson(listString , Array<String>::class.java).toList()
Log.e("GSON", lista[0])

I recommend use the StringTokenizer, is very efficient
List<String> list = new ArrayList<>();
StringTokenizer token = new StringTokenizer(value, LIST_SEPARATOR);
while (token.hasMoreTokens()) {
list.add(token.nextToken());
}

If you're using guava (and you should be, see effective java item #15):
ImmutableList<String> list = ImmutableList.copyOf(s.split(","));