Today's lab
Goals for today:
- practice problems similar to what will be on the midterm exam
- Where you see this icon, you can click it to check the problem in
Practice-It!
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).
12/5 + 8/4
|
4 |
|
2.5 * 2 + 17/4
|
9.0 |
|
41 % 15 % 7 + 17 % 3
|
6 |
|
21/2 + "7 % 3" + 17 % 4
|
"107 % 31" |
|
46/3/2.0/3 * 4/5
|
2.0 |
Exercise : Parameter Mystery
-
Fill in the boxes with the output that each method call would produce:
public class Mystery { 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
Consider the following Java code.
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);
}
Fill in the boxes with the output produced by each of the method calls.
ifElseMystery(10, 3);
|
0 3 |
|
ifElseMystery(6, 6);
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6 7 |
|
ifElseMystery(3, 4);
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-4 4 |
|
ifElseMystery(4, 20);
|
8 21 |
Exercise : while loop mystery
Fill in the boxes at right with the output produced by each method call.
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);
}
|
|
Exercise : assertions
Identify whether each assertion is always/never/sometimes true
at each point.
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);
}
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
Try solving this problem in Practice-It! from the link above.
Exercise : printMultiples
Write a static method called printMultiples that takes an
integer n and an integer m as parameters and that
prints a complete line of output reporting the first m
multiples of n. For example, the following calls:
printMultiples(3, 5); printMultiples(7, 3);should produce this output:
The first 5 multiples of 3 are 3, 6, 9, 12, 15 The first 3 multiples of 7 are 7, 14, 21
Notice that the multiples are separated by commas. You are to exactly reproduce this format. Also notice the order of the parameters: the first parameter is the base number and the second parameter is the number of multiples to generate.
You may assume that the number of multiples you will be asked to generate is greater than or equal to one.
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : digitsInARow
Write a static method called digitsInARow that takes an
integer n as a parameter and that returns the highest number
of digits that appear in a row in the base-10 representation
of n. For many numbers the answer will be 1 because they
don't have adjacent digits that match. But for a number like 3555585, the
answer is 4 because there are four occurrences of the digit 5 that appear
in a row. Below are sample calls on the method.
Method Value Method Value Call Returned Call Returned ------------------------------- ------------------------------- digitsInARow(0) 1 digitsInARow(8823) 2 digitsInARow(18) 1 digitsInARow(777) 3 digitsInARow(394) 1 digitsInARow(82888) 3 digitsInARow(99) 2 digitsInARow(7111171) 4 digitsInARow(8229) 2 digitsInARow(233333888) 5
You are not allowed to use a string to solve this problem. You may assume that the value passed to the method is greater than or equal to 0.
Hint: You can pull apart a number into its digits using /
10 and % 10.
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : allDigitsOdd
Write a method named allDigitsOdd that returns whether every
digit of a positive integer is odd. Your method should
return true if the number consists entirely of odd digits
and false if any of its digits are even. 0, 2, 4, 6, and 8
are even digits, and 1, 3, 5, 7, 9 are odd digits.
For example, allDigitsOdd(135319) returns true
but allDigitsOdd(9145293)
returns false.
Hint: You can pull apart a number into its digits using /
10 and % 10.
Solve this problem in Practice-It by clicking on the check-mark above.
Exercise : season
-
Write a method named
seasonthat takes two integers as parameters representing a month and day and that returns a String indicating the season for that month and day. Assume that months are specified as an integer between 1 and 12 (1 for January, 2 for February, and so on) and that the day of the month is a number between 1 and 31. -
If the date falls between 12/16 and 3/15, you should
return
"Winter". If the date falls between 3/16 and 6/15, you should return"Spring". If the date falls between 6/16 and 9/15, you should return"Summer". And if the date falls between 9/16 and 12/15, you should return"Fall". - Try solving this problem in Practice-It! using the link above.
Exercise : firstDigit
-
Write a method named
firstDigitthat returns the first digit of an integer. For example,firstDigit(3572)should return3. It should work for negative numbers as well. For example,firstDigit(-947)should return9. - Try solving this problem in Practice-It! using the link above.
- (Hint: This problem requires a loop.)