CS 1425 Lecture 1: Java Blockchain-Block Class

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rubyporcupine166

26 Apr 2019

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Java blockchain (block class) package basicblockchain; import java. security. import java. security. messagedigest; import java. util. import java. util. logging. level; import java. util. logging. logger; * @return bhash, a. k. a hash in block public string getbhash() { return bhash; //method containing algorithm for mining the blockchain with input integer. //diff used to determine difficulty of mining process (larger number = more. String a1; a1 = new string(new char[diff]). replace("\0", "0"); while (!bhash. substring(0, diff). equals(a1)) { bonce = bonce + 1; bhash = calchash(); String a = "mining complete of block:" + bhash; //turns values of a blockchain into a hash using sha-256 encryption private string calchash() { String a0 = string. valueof(bindex); a0 += string. valueof(bdate); a0 += bdata; a0 += string. valueof(bonce); a0 += blasthash; String a1; a1 = ""; try { a1 = sha256(a0); //method that turns string input into an encrypted hash using stringbuffer static string sha256(string in) throws nosuchalgorithmexception { Messagedigest encrypt = messagedigest. getinstance("sha-256"); byte[] encrypt0 = encrypt. digest(in. getbytes());

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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. Finally, you should write a program MontrealMaps which will suggest a path to go along the metro to get from one place to another. The only required method for MontrealMaps is a main method but of course you are allowed to write others. Your program should do the following. For any library methods that you use, make sure that you are properly importing things and handling any exceptions they may throw. (10 points) • Using an appropriate library method, you should create a Subway System object. If this method fails to initialize, you should print the message Error, not enough funding. • Use a Scanner and print statements to read the current x and y position of the user. • Use a Scanner and print statements to read the x and y position that the user wants to go to. . Find the nearest Metro Station to both the start position of the user and his final destination. • If the 2 metro stations have the same name (i.e. are the same metro station) then print It is fastest to walk there. • Otherwise, call the method findPath from the previous part to find a path from these 2 metro stations. . If the method returns null, then print Sorry, there is no path on the metro, you'll have to walk • Otherwise, print the path using the metro using the method printPath defined in the MapUtilities class in the appendix. SUMMARY OF JAVA STANDARD LIBRARY METHODS POR SELECTED CLASSES • String package java.lang) Methods - public boolean gist and e rs is stingeancoject - puble boolean grease Sering another ca t ering String paint i th Stre C h eshilly before the Stripe with striert w Single weiter water N ENE fusha -publish tohy Casting de . File( p age java.io) Methods r eate - publie Yiling path : C • Scanner (package java.ut 1) Method -ple S ule - double Double Sc - le bon when : S Scanner tal de fethede h able othebean - puble String Best Mus eethe u s tepal -pulle haalean haxtLine: Check the hea ther in left PrintStream( p age java.io) Methods pul vaid pri Pribonaat - puli wid pride d oble vile. - pille vaid print Print vei. -pulle vaid printject o: Prints Object -puli vaid printString : Prints String .. - vaid primi The theme line by writing the li n e tie id print in bool bl. Prise n value the - public void platinabled Prints double ved and then the line - public void printit Prints Ent value and then tomis the - Pull vaid pri l l be t he minime publie wild prin t ing with String in the terminates the line • ArrayLiat package java.util) Methods - public boolean Arraybettype was a new ArrayList

CS 1425 Lecture 1: Java Blockchain-Block Class

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