CSE 142: Computer Programming I, Autumn 2011

Homework 6 (Mad Libs) FAQ

Q: How do I get started?

A: Read Ch. 6 in the textbook. Look over the TA Hours worked example from lecture.

Q: Why does my prompt get all messed up when the user types more than one word on the console?

A: Make sure to choose the right method(s) for reading user input. If you want a one-word answer, use the Scanner object's next method. If you want to allow a multi-word answer, use nextLine instead.

Q: Why do I get a NoSuchElementException?

A: You tried to read past the end of a Scanner. Read the exception output text carefully and look for the first line that mentions your program. That's the line that is the culprit. For example, the output:

Exception in thread "main" java.util.NoSuchElementException
          at java.util.Scanner.throwFor(Scanner.java:838)
          at java.util.Scanner.next(Scanner.java:1347)
          at MyProgram.sillyMethod(MyProgram.java:39)
          at MyProgram.main(MyProgram.java:15)

means that there's an error in sillyMethod at line 39 of MyProgram.java.

Q: Why do I get an InputMismatchException?

A: You tried to read the wrong type of token from a Scanner. For example, you tried to read the word "Lisa" as an int.

Q: How do I make a Scanner start over or go back?

A: You can't! But if it is a String Scanner, you can make a new Scanner over the same String to start reading over again.

Q: How do I use a PrintStream?

A: See section 6.4 of the textbook. You just construct it and then call methods on it such as print and println, just like you do with System.out.

Q: How do I know which words are placeholders?

A: Any token that begins with a < and ends with a > is a placeholder.

How do I tell whether to print "a" or "an" for the prompt message? How do I change the - dashes in a placeholder into spaces?

A: String objects have lots of useful methods that can help you with these tasks. Most of them are ones we have seen a lot already, such as length, startsWith, substring, toUpperCase, and so on. You may also want to use the replace method on this assignment, which replaces all occurrences of one character with another. For example:

String str = "mississippi";
str = str.replace("s", "*");    // str = "mi**i**ippi"

Q: How do I view an existing mad lib?

A: Just read the input file and output all of its contents to the console. See the textbook Chapter 6 Self-Check problem #12, printEntireFile, for hints.

Q: How do I re-prompt if the input file is not found?

A: See the methods of File objects shown in the lecture slides. You can use these methods to detect whether or not a file exists and re-prompt if it does not.