Hello guys!
 I'm trying to make sketch with simple function of  word-wrap removal in txt files.
 The following code reads, join strings, writes, but not as it needs:
 I tried to make this additionally: when you give parameters how many old strings will be in 1 new - 5 or 10 old in 1 new string. Now the problem is: It writes to document only 2 new strings( last 7 joined old strings into 8th new), and new others it doesn't create. I am afraid I get confused because of "loops" and "may not have been initialized".
 This i use when I make 7 strings in one new:

for(int i = 1; i < lines.length/7 ; i++) { ... }
                     
 Next code for removing array out of bound exception - so the last or first 7 strings must be empty(spaced once and wrapped).

for(int ii = 0; ii <lines.length-6 ; ii++) {          
                                           ...
mystring = lines[ii] + lines[ii+1] + lines[ii+2] + lines[ii+3] + lines[ii+4] + lines[ii+5] + lines[ii+6];
                                            ...       }

Full Code:

String sevenStrings = new String();
String temp[];
String[] bigStrings;
String lines[] = loadStrings("loadsomefile.txt");
String[] neww= new String[lines.length/7];
for(int i = 1; i < lines.length/7 ; i++) {
  String currentstring;
  for(int ii = 0; ii <lines.length-6 ; ii++) {
    currentstring = lines[ii];
    String  mystring;
    mystring = lines[ii] + lines[ii+1] + lines[ii+2] + lines[ii+3] + lines[ii+4] + lines[ii+5] + lines[ii+6];
    String[] SevenStrings = { 
      lines[i], lines[i+1], lines[i+2], lines[i+3], lines[i+4], lines[i+5], lines[i+6]            }; 
    temp = append(SevenStrings,mystring);
    println(SevenStrings);
    saveStrings("writesomefile.txt", temp);
  }  
}  

                                    Any ideas appreciated!!!

Like many beginners, you make things harder and hard-code some stuff that the computer can do itself. If you have to change from 7 to 5, for example, you are in trouble...
Here is a simpler version of your code.
Code:

String lines[] = loadStrings("E:/tmp/loadsomefile.txt");
int joinBy = 7;

String[] neww = new String[lines.length / joinBy];
for (int i = 0; i < lines.length / joinBy ; i++) 
{
  String currentString = "";
  for (int ii = 0; ii < joinBy; ii++) 
  {
    // I would use a StringBuilder instead, but String is enough for this simple case
    currentString += lines[i * joinBy + ii] + " ";
  }
  neww[i] = currentString;
}
saveStrings("E:/tmp/writesomefile.txt", neww);
 

Note I have put saveStrings outside of the loop: in your version, each loop overwrite the previous content of the file...

Note: don't take bad my remarks about beginners... We all made the same errors, that's what make us to learn and improve.