Except where otherwise noted, the contents of this document are Copyright 2012 Stuart Reges and Marty Stepp.
lab document created by Marty Stepp, Stuart Reges, Whitaker Brand and Hélène Martin
Goals for today:
Which of the following choices is the correct syntax for printing an array of integers named a
as a comma-separated list of values enclosed in brackets?
Arrays
class methodsMethod name | Description |
---|---|
Arrays.binarySearch(array, value)
|
returns index of value in a sorted array (< 0 if not found) |
Arrays.copyOf(array, length)
|
returns a new copy of an array |
Arrays.equals(array1, array2)
|
returns true if the two arrays contain same elements |
Arrays.fill(array, value)
|
sets every element to the given value |
Arrays.sort(array)
|
arranges the elements into sorted order |
Arrays.toString(array)
|
returns a string for the array, such as "[10, 30, -25, 17]" |
What values are stored in the array at the comment in main
?
Note that the incrementAll
method returns void
, but does take an int[]
parameter.
public class ArrayReference {
public static void main(String[] args) {
int[] nums = {2, 4, -1, 3};
incrementAll(nums);
// HERE!
}
public static void incrementAll(int[] data) {
for (int i = 0; i < data.length; i++) {
data[i]++;
}
}
}
index | 0 | 1 | 2 | 3 |
---|---|---|---|---|
value | 3 | 5 | 0 | 4 |
Solve another reference mystery problem on PracticeIt!
Discuss it with your neighbor before submitting the answer and make sure you agree with each other's solution. There will be a problem of this type on the final!
swapAll
Write a method named swapAll
that accepts two arrays of
integers as parameters and swaps their entire contents. You may assume that
the arrays passed are not null and are the same length.
For example, if the following arrays are passed:
int[] a1 = {11, 42, -5, 27, 0, 89}; int[] a2 = {10, 20, 30, 40, 50, 60}; swapAll(a1, a2);
After the call, the arrays should store the following elements:
a1: {10, 20, 30, 40, 50, 60} a2: {11, 42, -5, 27, 0, 89}
copyRange
Write a method named copyRange
that takes as parameters two
arrays a1
and a2
, two starting
indexes i1
and i2
, and a length l
,
and copies the first l
elements of a1
starting at
index i1
into array a2
starting at
index i2
.
For example, if the following arrays are declared:
int[] a1 = {10, 20, 30, 40, 50, 60}; int[] a2 = {91, 92, 93, 94, 95, 96}; copyRange(a1, a2, 0, 2, 3);
After the preceding call, the contents of a2
would
be {91, 92, 10, 20, 30, 96}
. You may assume that the
parameters' values are valid, that the arrays are large enough to hold the
data, and so on.
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.
You should solve this problem in Practice-It!
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.
You should solve this problem in Practice-It!
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 |
// Counts the total lines and words in the given input scanner. public static void countWords(Scanner input) { Scanner input = new Scanner(new File("example.txt")); int lineCount = 0; int wordCount = 0; while (input.nextLine()) { String line = input.line(); // read one line lineCount++; while (line.next()) { // count tokens in line String word = line.hasNext; wordCount++; } } } |
The above attempted solution to Practice-It problem
"countWords
" has 5 errors.
Open Practice-It from the link above, copy/paste this code into it, and fix
the errors. Complete the code so that it passes the test cases.
Scanner
for the
filenextLine
should be hasNextLine
line
should be nextLine
Scanner
to read the tokens of
each linehasNext
should be next()
println
statements to print
line/word stats
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 |
// Counts the total lines and words in the given input scanner. public static void countWords(Scanner input) { |
coinFlip
Write a method named coinFlip
that accepts
a Scanner
for an input file of coin flips that are heads (H)
or tails (T). Consider each line to be a separate set of coin flips and
output the number and percentage of heads in that line. If it is more than
50%, print "You win!". Consider the following file:
H T H H T T t t T h H h
For the input above, your method should produce the following output:
3 heads (60.0%) You win! 2 heads (33.3%) 1 heads (100.0%) You win!
printDuplicates
Write a method printDuplicates
that accepts a Scanner
for an input file.
Examine each line for consecutive occurrences of the same token on the same line and print each duplicated token along how many times it appears consecutively. For example the file:
hello how how are you you you you I I I am Jack's Jack's smirking smirking smirking smirking smirking revenge one fish two fish red fish blue fish bow wow wow yippee yippee yo yippee yippee yay yay yay
leads to the following console output:
how*2 you*4 I*3 Jack's*2 smirking*5 wow*2 yippee*2 yippee*2 yay*3
mostCommonNames
Write a method mostCommonNames
that accepts a Scanner
for an input file with names on each line separated by spaces. Some names appear multiple times in a row. For example:
Benson Eric Eric Marty Kim Kim Kim Jenny Nancy Nancy Nancy Paul Paul Stuart Stuart Stuart Ethan Alyssa Alyssa Helene Jessica Jessica Jessica Jessica Jared Alisa Yuki Catriona Cody Coral Trent Kevin Ben Stefanie Kenneth
For each line, print the most commonly occurring name. If there's a tie, use the first name that had that many occurrences.
Most common: Kim Most common: Jessica Most common: Jared
Also return the total number of unique names in the whole file (e.g. 23 for the above input).
stripHtmlTags
Write a method stripHtmlTags
that accepts a Scanner
for an input file containing an HTML web page, then reads that file and prints the file's text with all HTML tags removed. A tag is any text between the character < and >. For example, consider the following text:
<html> <head> <title>My web page</title> </head> </html>
If a file containing these lines were passed to your program, your program should output the following:
My web page
wordLengths
Write a method called wordLengths
that accepts a Scanner representing an input file as its argument. Your method should read from the given file, count the number of letters in each token in the file, and output a result diagram of how many words contain each number of letters. Use tabs before the asterisks so that they'll line up. If there are no words of a given length, omit that line from the output.
You should solve this problem in Practice-It!
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!