Java代写：CE152 Exercises

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完成Java基础练习题，代写五个小程序。

Demonstration

You will be required to demonstrate your solutions to the assignment tasks in Week 30 (i.e. shortly after the submission deadline), please see this webpage for further information.

You will receive a mark of zero if you fail to demonstrate your work at the allocated time.

Extenuating Circumstances

The standard extenuating circumstances procedures will apply for those who ­for circumstances beyond their control ­ are prevented from submitting work before the deadline or from attending the lab demonstration. Please see the Undergraduate Students’ Handbook for the University policies regarding these matters.

1. Exercise

A pizza delivery service sells pizzas in two different sizes: medium and large. The prices for a basic pizza (without any toppings) are £4 (medium) and £5 (large).
Customers can choose up to four toppings from the list below. Toppings are optional ­ it should also be possible to order a basic pizza without any toppings.

medium large
ham £1.40 £2.10
mozzarella £1.00 £1.50
olives £0.80 £1.20
pineapple £1.00 £1.50
spinach £0.80 £1.20

Your task is to write a program that helps staff members to input a pizza order and which works out the price. The size of the pizza and the toppings are to be specified by initial letters.

Part A

Write a class Exercise1 with a method

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public static void pizzaServiceA()

The method should feature a loop. In each step of the loop, the program should

  • ask the staff to enter a pizza order, and then
  • display the order details as well as the pizza price.

Pizza orders should be entered as a sequence of up to 5 characters all on one line:

  • The first character should be either m (meaning medium) or l (meaning large).
  • This should be followed by zero to four characters indicating the pizza toppings. Each of these characters should be the initial character of one of the toppings. Multiple occurrences of the same topping should be allowed and charged accordingly.

For example, if the staff member inputs

mph

the program should respond with output as follows:

Medium pizza with pineapple, ham, £6.40

Multiple occurrences of toppings should be listed multiple times in the output, for example if the staff inputs

lsms

the program should respond with

Large pizza with spinach, mozzarella, spinach, £8.90

If the order has no toppings, this should be stated in the output, for example if the staff inputs

m

the program should respond with

Medium pizza with no toppings £4.00

Please format the price output so that it shows 2 digits following the decimal point.

The program should check that the user input is valid. If the user input is invalid, the program should display an informative message. It should not show any order details or the price in this case.

The program should terminate if the user enters the word quit.

Add a main() method to your class which invokes method pizzaServiceA(). Test your program.

Part B

In class Exercise1, add a method

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public static void pizzaServiceB()

The method should implement the same functionality as in Part A, but with one difference: it should not be allowed to place orders where one topping occurs three or more times. For example, the following order should be invalid because spinach occurs three times:

msmss

The program should print an informative message in this case.

Please note that orders where a topping occurs twice should still be allowed, so for example the following is a valid order:

lsoos

and the program output should be

Large pizza with spinach, olives, olives, spinach, £9.80

Add an invocation of pizzaServiceB() to the main() method. Test your program.

2. Exercise

Write a class Exercise2 with a method

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public static int[] closestToMean (double[][] array)

Given a rectangular 2D array, the method should first compute and print the arithmetic mean of all elements. It should then find the array element which is closest to the mean and print this. The method should return the row index r and the column index c of that array element in form of a two­element integer array [r,c].

For example, if the argument array has the following elements

3 -1 -4  0 
5 -2  9  6
8  2  4 -9

then mean=1.75. The array element closest to mean is the number 2, it has distance 0.25 from the mean. The method should print:

Mean = 1.75 
Closest array element = 2.0

The closest array element is in row 2 and column 1, hence the method should return an array with elements [2,1]. Note that counting of rows and columns starts at zero as usual in Java programming.

Hint. The “distance” of two numbers x and y can be computed in Java as Math.abs(x-y).

If there is more than one element with the minimal distance to the mean, then the method can return the row and column indices of any of these elements.
In class Exercise2, add a method

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public static void testClosestToMean()

This method should invoke closestToMean() for the sample array shown above. It should display the result.

Result = [2, 1]

In class Exercise2, add a main() method which invokes testClosestToMean(). Check that the result is correct.

3. Exercise

Part A

The Catalan numbers (https://en.wikipedia.org/wiki/Catalan_number) form a sequence of natural numbers that occurs in various combinatorial problems. They can be computed using the following two equations:

catalan(n) = 2 * (2 *n - 1) * catalan(n - 1) / (n + 1), if n > 0 
catalan(0) = 1

Create a class Exercise3 with a method

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public static long catalan(int n)

for computing the n’th Catalan number using the equations above. Your method should check the argument n and throw an IllegalArgumentException

In class Exercise3, write a method:

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public static void exercise3a()

The method should contain an interactive loop. In each step of the loop, the program should:

  • Ask the user to enter an integer n with 0<=n<=30 or quit to exit;
  • Check whether the user input is quit and exit the loop if this is the case
  • Otherwise parse the input as an integer n, invoke catalan(n) and display the result to the user

Method exercise3a() should not do any user input validation and no exception handling. You can assume that the user input is either quit or an integer.

Add a main() method to your class which invokes exercise3a(). Test your program both with some valid and some invalid integer inputs (= numbers that are less than 0 or greater than 30). The program should terminate with an IllegalArgumentException if the number input is invalid.

Part B

In class Exercise3, code a method:

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public static void exercise3b()

This method should perform the same task as exercise3a() above but with one difference ­ if the invocation of catalan throws an IllegalArgumentException, then it should catch this exception, print a suitable error message, and continue with the interactive loop.

Add an invocation of exercise3b() in the main() method. Test your program both with some valid and invalid integer inputs.

Part C

Write a class TestCatalan with one or more JUnit tests that check that method catalan(n) returns the correct result for six different arguments n. Restrict your testing to valid integer arguments.

Run TestCatalan in JUnit and check that your catalan function passes all the tests.

Note. JUnit testing will be covered during Week 24. You can find a list with some Catalan numbers at the On­Line Encyclopedia of Integer Sequences.

4. Exercise

The following online folder contains some mazes stored in separate files.

You should make copies of these three files in a convenient directory on your M: drive. Then take a look at the files. Each of them contains a quadratic maze with walls indicated by a #­symbol. As an example, here is file maze21.txt.

Part A

Write a class Exercise4 with a program that reads such a maze file into a two­dimensional boolean array. Then display the array on the console with one line for each row. Represent array elements using blank­symbols and #­symbols so that the console output has the same format as the maze file, see the example above.

You are free to add further classes or methods as you see fit.

Part B

Expand the program you wrote in Part A so that it displays the maze using Java2D graphics. Also draw a blue circle in the top­left corner so as to indicate the starting­point of the maze and a red circle in the bottom­right corner to indicate the target­point. The format should be similar to the image below.

Part C

Expand the program you wrote in Part B so that the user can traverse the maze using the arrow keys on the keyboard. The current position should be indicated by a filled blue circle. The keyboard control should work as follows:

  • Right­arrow: move blue circle to the right if possible.
  • Down­arrow: move blue circle down if possible.
  • Left­arrow: move blue circle to the left if possible.
  • Up­arrow: move blue circle upwards if possible.

The walls of the maze should be respected when traversing the maze ­ it should not be possible for the blue circle to go across a wall.

The GUI should also have a Reset button, see image below. Pressing this button should reset the current position and the blue circle to the initial position in the top left corner.

The program should display a congratulation message when the user reaches the red circle in the bottom­right corner. Use a JOptionPane to show this message,

Hints

Don’t forget to invoke method repaint() after making changes to the GUI. Also make sure that the component with the key listener gets the focus, see the Key Listener tutorial (https://docs.oracle.com/javase/tutorial/uiswing/events/keylistener.html).

5. Exercise

The online CSV (https://en.wikipedia.org/wiki/Comma­separated_values) file contains data about several thousands British and Irish hills.

You should make a copy of this file in a convenient directory on your M: drive. Then take a look at the file. Apart from the initial header row, each row describes a hill in the following format:

Number Name County Height (in metres) Latitude Longitude
255 Ben Nevis Highland 1344.5 56.796849 ­5.003525

In each row, the six fields are separated by commas. You can assume that there are no other commas in the CSV file.

Part A

Create a class Hill that represents the data for one hill as in file hills.csv. Each Hill object should have six fields corresponding to the columns in that file:

  • An integer number
  • A name
  • A county name
  • The height (in metres)
  • The latitude
  • The longitude

The class should also have:

  • A constructor with six arguments for initialising the six fields.
  • An instance method toString() which returns a string in the same format as the rows in the CSV file:
255,Ben Nevis,Highland,1344.5,56.796849,-5.003525

Then create a class Exercise5 with the following method:

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2
3
4
public static void exercise5a() { 
  Hill benNevis = new Hill(255, "Ben Nevis", "Highland", 1344.5, 56.796849, -5.003525); 
  System.out.println(benNevis); 
}

Add a main() method to class Exercise5 that invokes exercise5a(). Test your program by running the class.

Part B

In class Hill, write a method

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public static List<Hill> readHills()

The method should read the hill data from file hills.csv. It should skip the header row. For each row thereafter, it should create a corresponding Hill object. The method should return a list containing these objects in the same order as they are in the file.
In class Exercise5, create a method:

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public static void exercise5b()

This method should invoke readHills() and display the first 20 list elements on the console.
Add an invocation of exercise5b() in the main() method and test your program.

Hints

  • See Week 19 lecture notes for sample code for reading data from a CSV file.
  • Remember that classes Double and Integer have methods to parse a number from a string.

Part C

In class Exercise5, write a method

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public static void exercise5c()

The method should read the hill data from file hills.csv into a list using method readHills(). It should then start an interactive loop. In each step of the loop, the program should:

  1. Request the user to enter the name of a hill.
  2. Respond by printing to the console the details of all matching hills. A hill is said to be matching if its name starts with the string entered by the user. Matching should be case­insensitive.

The program should exit if the user enters quit. See a sample interaction below:

Please enter a hill name or quit to exit: 
Cadair 
1862,Cadair Berwyn,Powys,832.0,52.8806,-3.380993 
1863,Cadair Berwyn North Top,Denbighshire,827.0,52.883881,-3.380235 
1865,Cadair Bronwen,Denbighshire,783.4,52.901461,-3.372899 
1868,Cadair Bronwen NE Top,Denbighshire,700.0,52.906631,-3.358802 
1911,Cadair Idris - Penygadair,Gwynedd,893.0,52.699618,-3.908792 
4587,Cadair Fawr,Rhondda Cynon Taff,485.0,51.800059,-3.483636 
12140,Cadair Ifan Goch,Conwy,207.0,53.185429,-3.810762 
Please enter a hill name or quit to exit: 
sno 
1742,Snowdon - Yr Wyddfa,Gwynedd,1085.0,53.068496,-4.076231 
10028,Snougie of Long Hill,Shetland Islands,75.0,60.259782,-1.208551 
13597,Snokoe Hill,Northumberland,191.0,54.953663,-2.028509 
13802,Snoddle Hill,Rochdale,277.0,53.66063,-2.073073 
Please enter a hill name or quit to exit: 
quit 
Good-bye

Add an invocation of exercise5c() in the main() method and test your program.

Part D

Write a method

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public static void exercise5d()

The method should read the hill data from file hills.csv into a list using method readHills(). It should then:

  1. sort the list of hills by name in alphabetical order and print the first 20 elements of the list; and then
  2. perform another sorting of the list of hills but this time by height in descending order (=highest hills first) and then print the first 20 elements of the list.

Sorting should be performed by invoking method Collections.sort (https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#sort­java.util.List­) making use of appropriate implementations of interfaces Comparable and/ or Comparator which you will need to code.

Part E

In class Hill, write a method

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public static Map<String, Set<Hill>> hillsByCounty(List<Hill> hills)

Given a list of Hill objects, the method should return a map which associates each county with the set of hills in that county. The map entries should be sorted by county names and each of the sets of hills should be sorted by hill names.
Then write a method:

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public static void exercise5e()

The method should read the hill data from file hills.csv into a list using method readHills(). It should invoke method hillsByCounty with that list. This method invocation returns a map. For each of the first three counties in that map, the program should display:

  • The name of the county
  • The names and the height of the first three hills associated with the county in the map.

This should result in program output as follows:

### County: Aberdeen 
Anguston Hill 117.0 
Beans Hill 146.0 
Brimmond Hill 266.0 
### County: Aberdeenshire 
A'Chioch 1151.0 
Aitionn Hill 273.0 
Allt Sowan Hill 568.0 
### County: Anglesey 
Barclodiau 168.0 
Bron Alar 64.0 
Bryn Carmel 116.0