File I/O and Recursion

Which class is normally used to read a text file in this course?

Which statement opens data.txt for reading?

What does the first option of the previous question actually do?

Which exception must be handled or declared when constructing a Scanner on a File?

Which import is needed for the File class?

Which loop reads a file to the end, line by line?

This kind of loop is an example of:

What does new File("report.txt") do?

Which File method tells you whether a file or directory of that name exists?

Which statement creates a writer that overwrites any existing content?

Which statement creates a writer that appends?

What is the most likely consequence of forgetting out.close()?

Which PrintWriter method writes formatted output?

What is the advantage of try-with-resources?

A program cannot find marks.txt although the file is visible in the project folder. The most likely reason is:

Which pair of parts must every recursive method have?

What happens when the base case is never reached?

What is the value of factorial(4) for the definition given in the review?

How many times is factorial called in total when factorial(4) is evaluated?

What does this method return for mystery(4)?

public static int mystery(int n) {
    if (n == 0) return 0;
    return n + mystery(n - 1);
}

What does fib(5) return, with fib(0) = 0 and fib(1) = 1?

Why is the naive recursive fib inefficient?

What is printed?

public static void count(int n) {
    if (n == 0) return;
    System.out.print(n);
    count(n - 1);
}
// count(3);

And this one?

public static void count(int n) {
    if (n == 0) return;
    count(n - 1);
    System.out.print(n);
}
// count(3);

Why do the two previous methods print in opposite orders?

What does each recursive call receive of its own?

What does this method compute?

public static int f(int[] a, int i) {
    if (i == a.length) return 0;
    return a[i] + f(a, i + 1);
}

What is the base case of the recursive binary search given in the review?

Which problem is most naturally solved with recursion?

Which statement is true of recursion and iteration?

What does reverse("abc") return for the recursive definition in the review?

Which change would turn a correct recursion into a StackOverflowError?

What is printed?

public static int power(int b, int e) {
    if (e == 0) return 1;
    return b * power(b, e - 1);
}
// System.out.print(power(2, 5));

Write, in five lines or fewer, the code that opens scores.txt, sums all the integers it contains and prints the total, including the handling of the checked exception.

Explain the difference between new PrintWriter("log.txt") and new PrintWriter(new FileWriter("log.txt", true)), and give one situation where each is the right choice.

Draw the sequence of calls and returns for factorial(4), showing what each frame returns to the one below it.

Write a program GradeReport that reads a file students.txt whose lines have the form id,name,grade, builds a Student object for each line, and writes report.txt containing one formatted line per student (name left-aligned in 15 columns, grade with two decimals) plus a final line with the class average. Handle a missing input file gracefully and close both streams.

Write recursive methods sumDigits(int n) (the sum of the digits of n), isPalindrome(String s) (ignoring case) and gcd(int a, int b) (Euclid's algorithm: gcd(a,0)=a and gcd(a,b)=gcd(b, a mod b)). For each one, state the base case in a comment and test it in main.