java - Why do I need to use finally to close resources?

Question

Most of the time, the only thing I see a finally block used for is something like

FileInputStream f;
try{
    f= new FileInputStream("sample.txt");
    //something that uses f and sometimes throws an exception
}
catch(IOException ex){
    /* Handle it somehow */
}
finally{
    f.close();
}

My question is, if f's scope ends with the enclosing block, why do we need to close it in the finally?

Answer 1

Because garbage collection is not the same thing as resource cleanup.

For example, if you have a JDBC Connection object that goes out of scope, there's no signal sent to the database server to indicate that open cursors and connections are no longer needed. Without those messages, you'll eventually exhaust the number of cursors and connections available to you.

Same with file handles and any other resource. Clean up after thyself.