Exercise : reference mystery
public static void main(String[] args) {
int y = 1;
int x = 3;
int[] a = new int[4];
mystery(a, y, x); // 2 3 [0, 0, 17, 0]^0-9,+
System.out.println(x + " " + y + " " + Arrays.toString(a)); // 3 1 [0, 0, 17, 0]^0-9,+
x = y - 1;
mystery(a, y, x); // 1 0 [17, 0, 17, 0]^0-9,+
System.out.println(x + " " + y + " " + Arrays.toString(a)); // 0 1 [17, 0, 17, 0]^0-9,+
}
public static void mystery(int[] a, int x, int y) {
if (x < y) {
x++;
a[x] = 17;
} else {
a[y] = 17;
}
System.out.println(x + " " + y + " " + Arrays.toString(a));
}
Exercise : array simulation
Consider the following method:
public static void mystery(int[] array) {
for (int i = 0; i < array.length; i++) {
array[i] = i * array[i];
}
}
Indicate in the right-hand column what values would be stored in the int[] array after mystery() executes with the int[] array in the left-hand column passed in as a parameter.
{}
|
{}
|
|
{7}
|
{0}
|
|
{3, 2}
|
{0, 2}
|
|
{5, 4, 3}
|
{0, 4, 6}
|
|
{2, 4, 6, 8}
|
{0, 4, 12, 24}
|
Exercise : inheritance mystery
Assume the following classes have been defined:
public class A extends B {
public void method2() {
System.out.println("a 2");
}
}
|
public class D extends B {
public void method1() {
System.out.println("d 1");
}
}
|
public class C {
public String toString() {
return "c";
}
public void method1() {
System.out.println("c 1");
}
public void method2() {
System.out.println("c 2");
}
}
|
public class B extends C {
public String toString() {
return "b";
}
public void method2() {
System.out.println("b 2");
}
}
|
continued on the next slide...
Exercise : Groceries
Write a method name groceries that accepts as its parameter a Scanner holding an input file. The data in the file represents grocery items purchased along with their price and their discount category. Your method should compute and return a real number representing the total cost of the grocery items.
Each item is represented by three tokens: (1) the name of the item (a single word), (2) its discount category ("red" (10% off full price), "blue" (25% off full price), or "none" (no discount)), and (3) its full price. The casing of the discount category is not guaranteed (for example, we could see "red", "RED", "rED", "rEd", or any other casing of the word "red").
Example input:avocado RED 1 blueberries none 5 milk blue 2.00 cream red 1.00 cereal None 1.29This should return 9.59.
Exercise : reverseLines
Write a method called reverseLines that takes
a Scanner containing an input file as a parameter and that
echoes the input file to System.out with each line of text
reversed.
| Example input | Example output |
|---|---|
If this method works properly, the lines of text in this file will be reversed. Remember that some lines might be blank. |
,ylreporp skrow dohtem siht fI elif siht ni txet fo senil eht .desrever eb lliw .knalb eb thgim senil emos taht rebmemeR |
Scanners over Files effectively. Check out lab 5 to review String processing.
Exercise : isAllEven
Write a method called isAllEven that takes an
array of integers as a parameter and that returns whether or not all of the
values are even numbers (true for yes, false for
no).
| Output | |
|---|---|
| {18, 0, 4, 204, 8, 4, 2, 18, 206, 1492, 42} |
true
|
| {2, 4, 6, 8, 10, 208, 16, 7, 92, 14} |
false
|
Hint: check out lab 7 to review how to deal with arrays!
Another hint: When can we safely say that every number is even? When can we safely say that not every number is even?
Exercise : removeShorterStrings
Write a method called removeShorterStrings
that takes an ArrayList of strings as a
parameter and that removes from each successive pair of values the shorter
string in the pair. If there is a tie (both strings have the same length), your method should remove the first string in the pair. If there is an odd number of strings in the list, the final value should be kept in the list.
| {"four", "score", "and", "seven", "years", "ago"} | {"score", "seven", "years"} |
| {"here", "comes", "the", "sun", ":)"} | {"comes", "sun", ":)"} |
If you need reference to ArrayList methods, consult the cheat sheet! To review ArrayLists in general, check out Monday's slides!
Exercise : Grasshopper
Write a class Grasshopper that extends the Critter class. A Grasshopper sits still until it gets into a fight. Once it fights, it celebrates its victory by doing a "hop".
A "hop" consists of moving NORTH a certain number of times, then SOUTH the same number of times, then WEST one time. The hops starts with a height of 1 (N, S, W), but each subsequent fight causes the next hop to be larger by one. The second hop is: (N, N, S, S, W). After finishing the hop, the Grasshopper sits idle again until it gets into another fight.
If a Grashopper is sitting still, it fights with Attack.ROAR. If a Grasshopper gets into a fight in the middle of a hop (while it is not sitting still), it always returns Attack.FORFEIT.
Example sequence of moves:
CCCC (fights) NSWCCC (fights) NNSSWCCCCCCC (fights) NNNSSSWCC ...
Exercise : append
Write a method called append that accepts two integer arrays as parameters and that returns a new array that contains the result of appending the second array's values at the end of the first array.
For example:
public static void main(String[] args) {
int[] list1 = {2, 4, 6};
int[] list2 = {1, 2, 3, 4, 5};
int[] combined = append(list2, list1);
// combined stores {1, 2, 3, 4, 5, 2, 4, 6}
}
You can review arrays in lab 7!
Exercise : longestSortedSequence
Write a method called longestSortedSequence
that accepts an array of integers as a parameter and that returns the
length of the longest sorted (nondecreasing) sequence of integers in the
array.
For example:
public static void main(String[] args) {
int[] array = {3, 8, 10, 1, 9, 14, -3, 0, 14, 207, 56, 98, 12};
int longest1 = longestSortedSequence(array);
// longest1 is 4 (because of -3, 0, 14, 207)
int[] array2 = {17, 42, 3, 5, 5, 5, 8, 2, 4, 6, 1, 19}
int longest2 = longestSortedSequence(array2);
// longest2 is 5 (because of 3, 5, 5, 5, 8)
You can review arrays in lab 7!