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How to add characters in the middle of a word in an arraylist in java?

I'm practicing ArrayList's. I'm trying to make it so that every time is is in the ArrayList, it is then followed with not. For instance [is sky, is, this is blue, is is, is not] after running through the method comes out as [is not sky, is not, this is not blue, is not is not, is not not]. However, with my code right now it does not change. I am new to Java, so I would really appreciate any pointers!
class Main {
public static void main(String[] args) {
ArrayList<String> list = new ArrayList<String>();
list.add("is sky");
list.add("is");
list.add("this is blue");
list.add("is is");
list.add("is not");
System.out.println(replace(list));
}
public static ArrayList<String> replace(ArrayList<String> list) {
for (int i = 0; i < list.size(); i++) {
if (list.subList(i, i + 1).equals("is")) {
list.add(i + 1, " not");
}
}
return list;
}
}

First solve the simplest case. Forget the list for a moment and do the substitution with just one String.
String replaceOne(String original) {
return original.replace("is", "is not");
}
Test this method.
String replaced = replaceOne("sky is");
The test passes if this replaced variable is equal to sky is not.
Once you've guaranteed that, move on to the general case, with a list.
void replaceMany(ArrayList<String> original) {
for (int i = 0; i < original.size(); i++) {
original.set(i, replaceOne(original.get(i)));
}
}
Note that if you're running this inside a static method, the above methods need to be static (i.e. static void, static String).
With Java 8 you could also solve this problem differently. Instead of using the set method on the array list, you could use lambdas and a collector to get a modified list (preserve the original and get another list with the modified strings). Something like:
List<String> replaced = original.stream()
.map(s -> replaceOne(s))
.collect(Collectors.toList());

With Java 9, you can simplify your code as follows:
import java.util.List;
import java.util.stream.Collectors;
public class Main {
public static void main(String[] args) {
List<String> list = List.of(
"is sky", "is", "this is blue", "is is", "is not");
System.out.println(replace(list));
}
public static List<String> replace(List<String> list) {
return list.stream()
.map(str -> str.replace("is", "is not"))
.collect(Collectors.toList());
}
}
Output:
[is not sky, is not, this not is not blue, is not is not, is not not]

Because your if statement is always false. Method subList returns list that you compare with string in line:
list.subList(i, i+1).equals("is")

How to edit the contents of an ArrayList in-place while looping [duplicate]

This question already has answers here:
How to change value of ArrayList element in java
(7 answers)
Closed 6 years ago.
Assume I have an ArrayList of Strings that holds the words, "hello" and "world". I want to add the word "java" to the end of each.
I have tried to do it while looping, but did not succeed. Please suggest me a method for the same.
The other way, I found was to create a different ArrayList and copy contents, however I don't think is efficient in terms of space.
import java.util.ArrayList;
public class EditArrayListInLoop {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("hello");
arrayList.add("world");
/* This does not work */
/*for(int i = 0;i<arrayList.size();i++)
{
arrayList.get(i) += "java";
}*/
ArrayList<String> arrayList2 = new ArrayList<String>();
for(int i = 0;i<arrayList.size();i++)
{
String test = arrayList.get(i);
test += "java";
arrayList2.add(test);
}
System.out.println(arrayList2);
}
}

test += "java"; doesn't change the content of the String returned by arrayList.get(i). It creates a new String. Strings are immutable, so there isn't any way to change the String objects within the List. You can only replace them by new String objects.
Use arrayList.set(index,newValue) to replace the i'th element of the List:
for(int i = 0;i<arrayList.size();i++)
{
arrayList.set(i,arrayList.get(i)+"java");
}

I think you should manipulate the first list only. Using an another list is not an optimal solution.
Here's the code.
Output
[hellojava, worldjava]
Code
import java.util.ArrayList;
public class EditArrayListInLoop {
public static void main(String[] args) {
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("hello");
arrayList.add("world");
for(int i = 0;i<arrayList.size();i++)
arrayList.set(i, arrayList.get(i).concat("java"));
System.out.println(arrayList);
}
}
Please note that Strings are immutable. Whenever you change the content of String, you're not actually appending anything behind the scenes. You are creating a completely new String.
If the contents of your Strings are expected to change, then the advisable way is to use the StringBuilder class instead:
Documentation
The principal operations on a StringBuilder are the append and insert
methods, which are overloaded so as to accept data of any type. Each
effectively converts a given datum to a string and then appends or
inserts the characters of that string to the string builder. The
append method always adds these characters at the end of the builder;
the insert method adds the characters at a specified point.
Here's the code:
import java.util.ArrayList;
public class EditArrayListInLoop {
public static void main(String[] args) {
ArrayList<StringBuilder> arrayList = new ArrayList<StringBuilder>();
arrayList.add(new StringBuilder("hello"));
arrayList.add(new StringBuilder("world"));
for(int i = 0;i<arrayList.size();i++)
arrayList.set(i, arrayList.get(i).append("java"));
System.out.println(arrayList);
}
}
P.S.: If such synchronization is required then it is recommended that StringBuffer be used.

try using the set method.
ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("hello");
arrayList.add("world");
for(int i = 0;i<arrayList.size();i++)
{
String str = arrayList.get(i);
arrayList.set(i, str + " java");
}
for(int i = 0;i<arrayList.size();i++)
{
String str = arrayList.get(i);
System.out.println(str);
}

You are looking for:
arrayList.set(i, arrayList.get(i) + "java");
More info on ArrayList: https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

Java, get all variable values of a class

So I have a class called Test:
public class Test{
protected String name = "boy";
protected String mainAttack = "one";
protected String secAttack = "two";
protected String mainType"three";
protected String typeSpeak = "no spoken word in super class";
//Somehow put all the class variables in an Array of some sort
String[] allStrings = ??(all class' strings);
//(and if you feel challenged, put in ArrayList without type declared.
//So I could put in, not only Strings, but also ints etc.)
public void Tester(){
//Somehow loop through array(list) and print values (for-loop?)
}
}
As you can see, I want to put all the class variables in an Array or ArrayList (or something similar) automatically.
And next I want to be able to loop through the array and print/get the values.
Preferably using an enhanced-for loop.

As other said, don't do this. But this is how:
Class<?> cl = this.getClass();
List<Object> allObjects = new ArrayList<Object>();
for (java.lang.reflect.Field f: cl.getDeclaredFields())
{
f.setAccessible(true);
try
{
Object o = f.get(this);
allObjects.add(o);
}
catch (Exception e)
{
...
}
}
for (Object o: allObjects)
System.out.println(o);

If you really really need do this you need to use Reflection.
However a much better approach would be to store the values in a Map (probably a HashMap) and then you can query/set/etc them from that easily.

You can use Map or Hashmap to store variables and its values instead of Array or Arraylist
HashMap is an object that stores both “key/value” as a pairs. In this article, we show you how to create a HashMap instance and iterates the HashMap data.

Why not use a HashMap for the values and iterate through that?
Iterate through a HashMap

Do this.
String threeEleves = "sky";
String sevenDwarves = "stone";
String nineMortal = "die";
String oneRing[] = new String[] // <<< This
{
threeElves,
sevenDwarves,
nineMortal
}
or do this
// in some class.
public void process(final String... varArgs)
{
for (String current : varArgs)
{
}
}
String one = "noodles";
String two = "get";
String three = "in";
String four = "my";
String five = "belly";
process (one, two, three, four, five);

Transform Set<Keyword> into String[]

I have an object Keyword that stores a String with the text of the keyword and a set o keywords (Set<Keyword>) that I need to transform into a String array. Is there a quick/easy way to do this or I need to iterate the set and add each keyword one by one?
EDIT:
For those asking for Keyword class:
#Entity
public class Keyword {
// ...
#Basic
private String value;
// ...
// Getters & Setters
}

Every class that implements Collection intefrace (and that includes Set) has toArray() method:
String[] array= set.toArray(new String[0]);
In case of a set that is parametrized with some other type, e.g. Set<Keyword> you would have to do something like:
Keyword[] array= set.toArray(new Keyword[0]);
String[] stringArray= new String[array.length];
for (int i=0; i<array.length; i++) {
stringArray[i]= array[i].getThatString();
}

Try this:
String[] arr = set.toArray(new String[set.size()]);
... is what I would have said, if you had a Set<Object>.
No, there is no way to directly convert a Set<Keyword> to a String[] since there is no direct relationship between Keyword and String. You will have to iterate over the set:
String[] arr = new String[set.size()];
int i = 0;
for (Keyword word : set)
arr[i++] = word.toString();

If you use Guava, you may use this:
Lists.transform(Lists.newArrayList(theSet), Functions.usingToString())
.toArray(new String[theSet.size()])
And this only scratches the surface of what Guava can actually do.

There is no specific way to do this . You can either convert Set to Object[] using set.toArray and then iterate over the array
or
iterate over the set directly

You may need to add toString() method to your Keyword class as shown below. Or you can use a separate transformer class/method.
class Keyword {
private String value;
Keyword(String v) {
this.value = v;
}
public String toString() {
return value;
}
}
.
I would say iterate the set and add each keyword one by one is your best possible strategy.
System.out.println(toStringArray(set));
.
private static String[] toStringArray(Collection<?> set) {
String[] arr = null;
if (set != null) {
arr = new String[set.size()];
int i = 0;
for (Object o : set) {
arr[i++] = o.toString();
}
}
return arr;
}
.
However if you really want, you can have a dirty workaround as shown below. Only issue here is that your keyword value cannot contain comma (,) as it is used by split() method.
String str = set.toString();
str = str.substring(1, str.length() - 1);
String[] asStringArray = str.split(",");
System.out.println(asStringArray);

Looping in ArrayLists with a Method

With much assistance I have developed a method that makes anagrams and then adds them into an ArrayList.
public void f(String s, String anagram, ArrayList<String> array)
{
if(s.length() == 0)
{
array.add(anagram);
return;
}
for(int i = 0 ; i < s.length() ; i++)
{
char l = s.charAt(i);
anagram = anagram + l;
s = s.substring(0, i) + s.substring(i+l, s.length());
f(s,anagram,array);
}
}
The problem is when I attempt to use this function to make ArrayLists in a loop that adds Strings from one ArrayList to another, I get an error saying I can't use a void, and the method f() is void.
List<String> Lists = new ArrayList<String>(); //makes new array list
for(String List : words)
{ //takes values from old array list
List.trim();
Lists.add(f(List,"",new ArrayList<String>())); //this is where it doesn't work
}
Let me clarify once more:
I want to use this function to insert ArrayLists of anagrams into each position in another ArrayList. The anagram Lists are derived from Strings that are being read from one list to another. I tried changing the method to static but that doesn't work, I also removed the return; in the method once, but that doesn't fix it either.
How do I make this whole thing work?

The error happens because the method f() is void, meaning: it doesn't return any value that can be added to the ArrayList.
The answer of invoking f() is stored in the ArrayList passed as a parameter to f, you should probably use that ArrayList to add all of its elements to Lists. Something like this:
List<String> lists = new ArrayList<String>();
for (String list : words) {
list.trim();
ArrayList<String> answer = new ArrayList<String>();
f(list, "", answer);
lists.addAll(answer);
}

Your method header for F needs to look like this:
public String f(String s, String anagram, ArrayList<String> array)
And then you return a String value to add to that ArrayList you are using.

Your function definition for f() shows the return value of type void. So looking at your code you're attempting to do this:
Lists.add(void);
which is obviously illegal.
Your choice really is to have the ArrayList declared in a greater scope.
private List<String> anagrams;
public void f(String s, String anagram) {
...
anagrams.add(anagram);
...
}
....
for(String List : words) {
//takes values from old array list
anagrams = new ArrayList<String>();
List.trim();
f(list,"");
Lists.add(anagrams); //this is where it doesn't work
}