android studio ask for external storage permission

1pickimage.setOnClickListener(new View.OnClickListener() {
2    @Override
3    public void onClick(View v) {
4      if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED)
5      {
6        ChoosePicture();
7      }else{
8        String[] myPermission={Manifest.permission.READ_EXTERNAL_STORAGE};
9        requestPermissions(myPermission,750);
10      }
11	
12    }
13});
14
15//if(checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED) is asking if permission to read External Storage is granted
16//if yes execute method ChoosePicture(); and choose a pictrue from your device
17//if not ask for permission by copy_paste the code in the else brackets
18//in requestPermissions(myPermission,750); you can send any number other than 750 it doesnt matter
19