CMPT 100 Lecture : CMPT 100

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blushchimpanzee546

3 Mar 2012

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Set of techniques for understanding these big problems. 2 major problems: not solving the right problem, not solving the problem right, syntax, semantic. Find errors by creating suites of test data that will reveal them. Ex. making a certain car that has to withstand all different kinds of weather across the world (-40oc in saskatoon and high rains in the tropics) Trying to figure out data by which to make ur program fail->esp hard for the person who created the program->often why it is a separate team who tests the program. Debugging is getting rid of the error while testing is finding the prob. Put in write statements ( say or think in scratch) Use a debug package-some more advanced programs can go step by step when pushing the space bar, scratch however can set single stepping to flash blocks (slow) . Managing the complexity by small steps rather than making the big product at once.

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4. In this question, you will be shown a snippet of code. You will then be shown the output from either the compiler or the Java virtual machine and be asked what the error is and how to fix it. In each case, your answer should include the line number of the problem, a one or two sentence explanation as to why the issue occurs, and a specific fix for the problem. Your fix should mention the exact line or lines of code you'd add/change/delete. Total for this question (5 parts): (15 points) (a) Consider the following class: import java.util.Scanner; public class Hockeystandings //This method should calculate the percentage of games in which the team lost. public static double computePercentageLosses (int numwins, int numLosses) return numLosses/ (numwins + numLosses) * 100; public static void main(String[] args) { Scanner reader - new Scanner (System.in); System.out.println("Enter the number of wins for the Maple Leafs"); int numLeafwins = reader.nextInt (); System.out.println("Enter the number of losses for the Maple Leafs"); int numLeaflosses-reader.nextInt (); System.out.println("Enter the number of wins for the Canadiens"); int numCanadienswins – reader.nextInt (); System.out.println("Enter the number of losses for the Canadiens"); int numCanadienslosses = reader.nextInt (); double mapleLeafs Record - computePercentage Losses (numLeafwins, numLeaf Losses); double canadienskecord - computePercentage Losses (numCanadienswins, nuCanadienslos305): if (canadiens Record > mapleleafsRecord) { System.out.println("Of course the Leafs did worse."); else { System.out.println("Wow, that hasn't happened for a long time!"); The point of the program is to ask the user to enter numbers representing the wins and losses of the Maple Leafs and Canadiens in a season. The code compiles successfully and when you run the program, you enter the values: 2 80 40 42 into the keyboard. You expect that the program will output the message Of course the Leafs did worse since they had fewer wins. However, to your surprise, the output of the program is: Wow, that hasn't happened for a long time! Why is this the case and fix the error?

9. Write a method with the following header public static void replace (String oldFile, string newfile, char oldChar, char newChar) throws IOException This method opens the file whose name is given by the String parameter oldFile (the input file) for reading, and opens the file whose name is given by the string parameter newlile (the output file) for writing. It then reads every lime in the input file. For each line, it creates a new line identical to the original line, creept for the fact that all occurrences of char oldchar in the original String have been replaced by occurrences of char newchar in the new line. When the new line has been properly created, it write it to the output file. Once all the lines in the input file have been read and a corresponding line has been written to the output file, the method clases both files. Additional notes: • You MAY assume that none of the parameters this method accepts are null; in other words, your method does not have to handle the case where one or more of the parameters are null. You MAY assume that all the 10-related classes have already heen imported properly . Finally, because the replace() method is specified to throw an exception object of type TORxception, you MAY assume that I/O related problems will occur while reading from the input file or writing to the output file. In other words, your method DOES NOT have to check that no such problems occur, and DOES NOT have to manage Texceptions using try-catch blocks. WRITE YOUR replace() METHOD IN THE SPACE BELOW: YOUR replace() METHOD CONTINUED: USE THIS PAGE IF YOU NEED ADDITIONAL SPACE. CLEARLY INDICATE WHICH QUESTION(S) YOU ARE ANSWERING HERE. USE THIS PAGE IF YOU NEED MORE ADDITIONAL SPACE. CLEARLY INDICATE WHICH QUES- TION(S) YOU ARE ANSWERING HERE. • String (package java.lang) Methods: - public String chal wale Al t ri g od med in the chance au - public int length(): R e ach of the string - public char chattin R echar w heefd index public chart to Chachay: Consthis String to a new c r y - public boolean equals Object anbject): Ce this string to and yect - public boolean equalsigmoce Case String anotherstring]: Cam p ing sider this String to anotherString - public int compareToString anotherString: Compare this String to anotherstring graphically returns a negative ef this string before anotherstring, apithe value of this Stringatering distries publie iw paneelgoro (String another Camp i ng Garden ces, string to anoth i ng li hically returns te value of this thing care anotherstring, apie as if this string e r anotherstring, Strings - public int indexin ch Rather within this string of the och ch-lil does not - public int index fint.ch, int from index): Returns the index within this string of the first Roe of character ch, starting the search at position from Index retums - 1 il ch does not in this String - public int indexor (String ste): Returns the index within this string of the first currence of ringt-d eur - public int indexOf(stringate, int from index): Resures the index within the string of the fare currence of shariaparting police froiden liste des not count i ng - public String subat ring it begintndax) Rema new string which is a webstring of this string compend of the chesting at position begintndex (inclusive) - puble string subat ring intaginindex intendindex: Returns a new sering that waring of this string, composed of the characters starting at position beginIndex (inclusive, and ending at - public String replace(char oldChar, char newchar): Returns a new string resulting from replacing a Tences of olchar in this string with new Char. puble string tolon Case(): Returns a new string consisting of all the characters in this sting - publle ting toppe : Roum ingiting of all the c on in this thing uverted to perce - publie ting tet): Returns a copy of this line with leading and wailing whitespace • Scanner (package java.util) Methods: - publie danner File source) thrown jatorio Foundation sa Scanner the fun the specified file - public scanner InputStream source): Cits Scanner that process and from the input stream - puble Scannerstag source): Corsa ww Scanner that produces wales w ed from the specified String -puble vold close(): Cwes this Scanner -puble boolean asext(): Return this can het in its input puble boolean asext.Double(): Return to the taken in this season al ante pasadala w ith Doble() ed publie boolean hat Into: Reutte le inse gule ed wat w eet Int() had - public boolean hati : Return true if this w ee - puble boolean has longt) Return true if the r in this cannerm ane das along the next long) with puble ting at the t e rm from the canner puble double Smerthea ter puble intention there the l ot. puble w ith the need them - puble Intolog m u long • Printstream ( kape Java.io) Methods: a - Pri le rlle) throw alo.Pilo t Pelat ihan the p rile - Printing the throw r alo. Pet Stichw e d the wind - le void lose them - le void phone boolean ve - void prichar public void print chart 6): the way of char public void print double d o uble bed, public void print (int ) Fins int value - public void printet a n net public void printing : Strings - public void printin (1 Tm the line by writing the line para ring - public void printinhoolna ) Prints hoolean when thinorminates the public void printin (cthar c h ar wheelthening the line public void print in char i ta way of cars and then the line public void print in double d in double valued and the terminates the line public void printin(int 1) Pints int value and then into the line public void printin ( jat ova t terminates the line pulle void print intring): Tits Strings then to the line Note that the printwriter class defines the same methods and constructors (except for the fact that the structors are called Print.writer instead of PrintStream) • Math (package java.lang) Methods: - please le podle double bear the value of a t the of - puble balle blanche a Returns they u se of dele with pe r than realto - pietate double random Ruma doble 0.0 wi th .. puble stat la doble sin double a: Rethe puble statie doble con double a Return ther l e, where a ininin we angle, wherea in in e -puble statie doble tan double a) R he i ngold , whereas o m public statie double toeges double agrad): C a ngrad v ideo puble salle de anable and we a r e - - estatie delle au t olewa idle de ahholooble • Character (packape java.lang) Methods: - public static boolean ibigit charch: D i chtechisadil public static int digit(charch, int radix: Return the meal of cho ch in the di radix-lich des representa digit - public statie char forbigit chat digit, ut radix) Rems the character of digit in the disa - public statie boolean isletter charch): Demines if character chalet publle statie boolean islowerCase(char ch): Determines if character ch is a character - public static boolean ipparate(char eh): Determines ir ductes chinuppercase cura nd - publicatie boliwhip (arch Termine if character his white a intola - public static char tolowrane(char chevert hech to low - public static char tolpperCase(char ch): Covers Chococh topp • Array list (package java.util) Methods: - public ArrayList(): Create a new em ArrayList which contains clements of type - public int (1 : R m the number of clans in this list - public boolean isimpty(): Rens true if this in contains no elements - public boolean contains (object o): Return true if this lintutins el compr a re performed using the equals() method on - public int IndexOf(obj ): Returns the index of the first currence of elemento in this list, or lir this listes contain this element companies are performed wing the equals() method - publiek galimt in ): Returns the elementat position index in this list - publieket fint inde element): Replace the element at the position index in this list with the - puble honlanad a ): Appends the specifiedalent to the end of this list. - public void (int in aw e t the specified element the price index in this - publiek veint index): Remove the de s ition index in the list - publie hoolean remove(object a s the fir e of the president of this if it is p r epared wing the equals() methodno - public void clear(): Remes all of the elements from this • Vile (package java.io) Methods: - puble File(String pathname: Creates a File representing the file at the given pathane

CMPT 100 Lecture : CMPT 100

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