объединил 2 массива в один и записал
вроде правильно но валидацию не проходит
package com.javarush.task.task18.task1819;
/*
Объединение файлов
*/
import java.io.*;
import java.util.ArrayList;
import static java.lang.System.arraycopy;
public class Solution {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String fileAdress1, fileAdress2;
fileAdress1 = reader.readLine();
fileAdress2 = reader.readLine();
FileInputStream fileInputStream1 = new FileInputStream(fileAdress1);
FileOutputStream fileOutputStream1 = new FileOutputStream(fileAdress1);
FileInputStream fileInputStream2 = new FileInputStream(fileAdress2);
int i;
int count = 0;
byte[] filebytes = new byte[fileInputStream1.available()+fileInputStream2.available()];
byte[] file1bytes = new byte[fileInputStream1.available()];
byte[] file2bytes = new byte[fileInputStream2.available()];
while(fileInputStream1.available()>0){
fileInputStream1.read(file1bytes);
}
while(fileInputStream2.available()>0){
fileInputStream2.read(file2bytes);
}
for(int j = 0; j < file1bytes.length; j++){
filebytes[j]=file1bytes[j];
}
for(int j = file1bytes.length; j < filebytes.length; j++){
filebytes[file1bytes.length]= file2bytes[j-file1bytes.length];
}
fileOutputStream1.write(filebytes);
}
}