CDN 4101 Study Guide - Midterm Guide: Static Variable, Type Signature, Javac

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13 Oct 2017

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Double, float, short, long, byte, int, boolean, character. Static and final, static indicates an attribute or method to belong to the class. Make a class with a main method (public static void main(stirng[] args){}) Open command line, javac filename. java which compiles the english java language to machine language which the jvm is able to read and run. Java filename is than called in order to run the file with the jvm. In order for the jvm to be able to read the file, the main method must be public because that is where the code is driven, otherwise the code wont compile. Because, in java a function or variable in class in inaccessible until an object is created from the class, but the "main" function is supposed to run at startup(without. So the "main" is declared public as well as static so that it can be accessed outside class & without even an object is created.

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(c) Consider the following class: public class Student Grades private int ( grades; 1/loads values into grades from a file public void initializeFromFile(String filename) ....! //gets the total number of grades entered public int get NumRecords () (....) public class WebCT 1 public static void main(String[] args) Student Grades grades = new Student Grades(); grades.initializeFromFile("records. L.sv"); System.out.println("There are " + grades.length file.") " grades in that The goal of the program is to load the files and then print the total number of grades in the file. However, when you try to compile the above classes, you get the following error: WebCT.java:5: cannot find symbol symbol : variable length location: class Student Grades System.out.println("There are " + grades.length + " grades in that file." Explain why the crror occurs and write the code to fix it (while maintaining the intended functionality).

(b) Consider the following classes: public class House - ي شما هر چند = = private String rooms; public House() String rooms - new String [31; rooms (0) - "living room"; rooms [1] - "kitchen"; rooms (2) - "bedroom"; = public void print RoomList () for (int i-0; i < rooms.length; i++) { System.out.println (rooms[1]); = ہم نوا شهيد - public class Block يا نو public static void main(String[args) له House myblouse - new House(); myHouse.print RoomList(); د ه د The program compiles, but when you run the program, you get the following exception: Exception in thread "main" java.lang.NullPointerException at House.print RoomList (House.java:12) at Block.main (Block.java:6) The point of the method printRoomList is to print all the Strings in the house to the screen. Why does it give the error and write the code to fix the error while successfully printing all the rooms to the screen?

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?

CDN 4101 Study Guide - Midterm Guide: Static Variable, Type Signature, Javac

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