Lambda expressions - Java 8 in Action: Lambdas, Streams, and Functional-Style Programming - page 59

Processing one line:
String oneLine =
processFile((BufferedReader br) -> br.readLine());
Processing two lines:
String twoLines =
processFile((BufferedReader br) -> br.readLine() + br.readLine());
Figure 3.3 summarizes the four steps taken to make the processFile method more flexible.
Figure 3.3. Four-step process to apply the execute around pattern