Setting file permission from java- Annoying issue

I am accessing png images from a directory using java code. The directory is created by me and the files are placed to this directory by me. There are no permissions set for the directory or files.

While I access the files, I get permission denied exception. In order to confirm, I printed the read and write permission of all the files in this directory. For few files, it has read and write permissions while for others, it returns false for read and write permissions.

In order to resolve the permission denied/file not found issue, I set the permission manually using different means.

Method 1

Runtime.getRuntime().exec("su chmod 777 " + ico); 

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I check the read & write permission after this, it is false again!

Method 2

Process chperm;
chperm=Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(chperm.getOutputStream());
os.writeBytes("chmod 777 " + ico +"\n");
os.flush();                                  
os.writeBytes("exit\n");
os.flush();
chperm.waitFor();

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I check the read & write permission after this, it is false again!

Can someone kindly let me know, why this happens and what is the solution I have for this. This turns out to be a literally annoying issue, as it has already eaten up some days of mine.

Any help in this regard which would lead me to the correct solution is much appreciated. I am even willing to give 500+ points for the correct solution!!

PS: All this code is executed from an android app