for(Integer x : lista)

that's called for-each loop and means basically for each element in the container lista named x do the following { /* code in the loops body */ } So it just iterates over the elements in a container and creates for each element a variable, in your example x that you can use in the body. Example:

// declaring a String array and looping over it, in each iteration an element is taken as s from the array
// but without an index you can not modify the current value inside the array (if it is an object you can not change the reference but work on the object itself)
for (String s : new String[]{"first", "second", "third"})
    System.out.println(s);