University of Washington, CSE 142

Lab 5-5: midterm practice

Except where otherwise noted, the contents of this document are Copyright 2013 Stuart Reges and Marty Stepp.

lab document created by Marty Stepp, Stuart Reges and Whitaker Brand

Basic lab instructions

• Mouse over highlighted words if you're not sure what they mean!
• Talk to your classmates for help.
• You may want to bring your textbook to future labs to look up syntax and examples.
• Stuck? Confused? Have a question? Ask a TA for help, or look at the book or past lecture slides.
• Complete as much of the lab as you can within the allotted time. You don't need to keep working on these exercises after you leave.
• Feel free to complete problems in any order.
• Make sure you've signed in on the sign-in sheet before you leave!

Today's lab

Goals for today:

• practice problems in the same format as the midterm
• find resources to help tackle exam problems

Exam Tips

• Practice problems with pencil and paper. You will not be coding on a computer for the midterm. Many students find it extremely difficult to code on paper for the first time on exams.
• Do not use "" around output (for example, in parameter mystery). But for expressions problems, make sure to put "" around Strings, and a decimal (ex. 2 ==> 2.0) for doubles. We require this to test your knowledge of what type an expression has.
• Review the cheat sheet. It will have all the syntax you need, but you'll need to know how to use it.
• No abbreviations/shorthand is allowed except for A/S/N for Always/Sometimes/Never in the assertions problem and S.o.pln() / S.o.p() for System.out.println() / System.out.print().
• More information on the Exams tab of the course website!

Exercise : Expressions

For each expression in the left-hand column, indicate its value in the right-hand column. Be sure to list a constant of appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).

If you've forgotten how to tackle expressions problems, check out lab 2 for a recap!

Also, make sure you can evaluate boolean expressions.

4

9.0

6

"107 % 31"

2.0

true

false

true

Exercise : Parameter Mystery

(Review this type of problem in lab 3!) Fill in the boxes with the output that each method call produces:

public static void main(String[] args) {
    String hear = "bad";
    String song = "good";
    String good = "hear";
    String walk = "talk";
    String talk = "feel";
    String feel = "walk";
    claim(feel, song, feel);       // to walk the walk is good
    claim(good, hear, song);       // to hear the good is bad
    claim(talk, "song", feel);     // to feel the walk is song
    claim("claim", talk, walk);    // to claim the talk is feel
}
public static void claim(String hear, String good, String song) {
    System.out.println("to " + hear + " the " + song + " is " + good);
}

Exercise : if/else mystery

public static void ifElseMystery(int a, int b) {
    if (a < b) {
        a = a * 2;
    }
    if (a > b) {
        a = a - 10;
    } else {
        b++;
    }
    System.out.println(a + " " + b);
}

0 3

6 7

-4 4

8 21

Exercise : while loop mystery

Fill in the boxes at right with the output produced by each method call. (Review how to do this type of problem in lab 5!)

public static void mystery4(int n) {
    int x = 1;
    int y = 2;
    while (y < n) {
        if (n % y == 0) {
            n = n / y;
            x++;
        } else {
            y++;
        }
    }
    System.out.println(x + " " + n);
}

1 2

1 5

4 3

3 7

Exercise : assertions

Write always/never/sometimes true at each point. If unsure how to, check out the assertions tutorial!

public static void mystery(int x, int y) {
    int z = 0;

    // Point A
    while (x != y) {
        // Point B
        z++;
        if (x > y) {
            // Point C
            x = x / 10;
        } else {
            // Point D
            y = y / 10;
        }
    }

    // Point E
    System.out.println(x + " " + y + " " + z);
}

You can also solve this problem in Practice-It by clicking on the check-mark above.

Exercise : makeGuesses

Write a method named makeGuesses that will output random numbers between 1 and 50 inclusive until it outputs one of at least 48. Output each guess and the total number of guesses made. Below is a sample execution:

guess = 43
guess = 47
guess = 45
guess = 27
guess = 49
total guesses = 5

If you're not sure how make/use a Random, review them here.

Exercise : seeMovie

You're thinking about going with your friends to a movie. Write a Java method seeMovie that accepts two parameters: the cost of a ticket in dollars, and the rating number of stars the movie received out of 5. The method should print how interested you are (very, sort-of, or not). Use the following criteria:

• You like bargains. Any movie that costs less than $5.00 is one that you want to see very much.
• You dislike expensive movies. You are not interested in seeing any movie that costs $12.00 or more, unless it got 5 stars (and even then, you are only sort-of interested).
• You like quality. You are very interested in seeing 5-star movies that cost under $12.00.
• You are sort-of interested in seeing movies costing between $5.00 - $11.99 that also got between 2-4 stars inclusive.
• You are not interested in seeing any other movies not described previously.

Exercise : swapPairs

Write a method named swapPairs that accepts a String as a parameter and returns that String with each pair of adjacent letters reversed. If the String has an odd number of letters, the last letter is unchanged. For example, the call swapPairs("forget") should return "ofgrte" and the call swapPairs("hello there") should return "ehll ohtree".

If you finish them all...

If you finish all the exercises, try out our Practice-It web tool. It lets you solve Java problems from our Building Java Programs textbook.

You can view an exercise, type a solution, and submit it to see if you have solved it correctly.

Choose some problems from the book and try to solve them!