Difference between the two code below

Hello Every one,

I am a confused betwwen the below 2 code.

Code 1:

while ((sCurrentLine = finput.readLine()) != null) {
System.out.println(sCurrentLine);
}

It display me the file content.

Code 2:

while ((finput.readLine()) != null) {
sCurrentLine=finput.readLine();
System.out.println(sCurrentLine);
}

Return me null value.

Could you please explain me the difference between this code.