Exam 2 Review

Class Activities 1- Update the attached code by adding an interface called "Named" which contains a method called "getNamed". Make BankAccount, Coin and BritishBankAccount implement the interface. 1.1- Code provided: Origin: src  1(test(folder)/Test(class)) 2(util(folder)/2.1BankAccount(class)- 2.2BritishBankAccount-2.3Coin(class)/2.4Measurable(interface)) Code: (no changes are going to be made) package Test; import util.BankAccount; import util.BritishBankAccount; import util.Coin; import util.Measurable; import java.util.ArrayList; public class Test { public static void main(String[] args){ ArrayList<Measurable> items = new ArrayList<>(); items.add(new BankAccount(100)); items.add(new Coin(.25, "Quarter")); items.add(new BritishBankAccount(100)); for(Measurable item: items) System.out.println("This item is a " + item.getClass().toString().split("\\.")[1] + " and its measurement is " + item.getMeasure()); } } package util; public class BankAccount implements Measurable{ @Override public double getMeasure() { return balance; } private double balance; public double getBalance(){ return balance; } public void deposit(double val){ balance += val; } public void withdraw(double val){ balance -= val; } public BankAccount(double balance){ this.balance = balance; } } (no changes are going to be made because once interface is implemented to bank account this one will inherit it) package util; public class BritishBankAccount extends BankAccount{ public BritishBankAccount(double balance) { super(balance); } @Override public double getMeasure(){ return super.getMeasure() * Measurable.GBP_TO_USD;

} } package util; public class Coin implements Measurable{ private double value; private String name; @Override public double getMeasure() { return value; } public Coin(double value, String name){ this.value = value; this.name = name; } } package util; public interface Measurable { public double getMeasure(); public double INCH_TO_CM = 2.54; public double GBP_TO_USD = 1.20; } 1.2 Answer: Origin: src  1(test(folder)/Test(class)) 2(util(folder)/2.1BankAccount(class)- 2.2BritishBankAccount-2.3Coin(class)/2.4Measurable(interface)/ Named(interface)) Code: (Named interface added) package util; public interface Named { String getName(); } package util; public class BankAccount implements Measurable, Named { @Override public double getMeasure() { return balance; } private double balance; public double getBalance(){ return balance; } public void deposit(double val){ balance += val; } public void withdraw(double val){ balance -= val; } public BankAccount(double balance){ this.balance = balance; } private String name; @Override public String getName(){ return name; } }

public int compareTo (Object aStudent) { if(!aStudent.getClass().equals(this.getClass())).  checks that they are the same kind class, object throw new IllegalArgumentException("can't compare a student with a " + aStudent.getClass()); Student other = (Student) aStudent; if(this.gpa.compareTo(other.gpa) != 0) return this.gpa.compareTo(other.gpa); if(this.lastName.compareTo(other.lastName) != 0) return this.lastName.compareTo(other.lastName); if(this.firstName.compareTo(other.firstName) != 0) return this.firstName.compareTo(other.firstName); return this.id.compareTo(other.id); } } } public class Main { static Student [] list = getList(); static Student [] getList() { // unknown implementation . . . } public static void main (String []args){ Arrays.sort(list); for(Student s: list) System.out.println(s); } } 3- Use the following class to create a class for DateTime representing a certain time in a certain date. Override the toString method ("mm/dd/yyyy @ hh:mm:ss PM/AM") and implement the Comparable interface for it. 3.1 Code Provided package util; public class Date implements Comparable<Date>{ private int day; private int month; private int year; @Override public String toString() { return String.format("%02d/%02d/%04d", month, day, year);

} public int getDay() { return day; } public int getMonth() { return month; } public int getYear() { return year; } public Date(int day, int month, int year) { this.day = day; this.month = month; this.year = year; } @Override public int compareTo(Date other) { if(this.year != other.year) return this.year - other.year;//new Integer(year).compareTo(other.year); if(this.month != other.month) return this.month - other.month; return this.day - other.day; //return (this.day - other.day) + 31 * (this.month - other.month) // + 372 * (this.year - other.year); } } 3.2 Answers in Red package util; public class DateTime implements Comparable<DateTime>{ private Date date; private int hour; private int minute; private int second; private boolean am; public DateTime(Date date, int hour, int minute, int second, boolean am) { this.date = date; this.hour = hour == 12? 0:hour; this.minute = minute; this.second = second; this.am = am; } @Override public String toString() { return String.format("%s @ %02d:%02d:%02d %s", date, hour == 0?12:hour, minute, second, am? "AM": "PM"); } @Override public int compareTo(DateTime other) { if(this.date.compareTo(other.date) != 0) return this.date.compareTo(other.date); if(this.am != other.am) return this.am?-1:1; if(this.hour != other.hour) return this.hour - other.hour; if(this.minute != other.minute) return this.minute - other.minute; return this.second - other.second; } }

5.2 Answer: last: i=4 6-Predict the outcome of the following: 6.1 Code provide: import java.util.*; public class Student { public static void main(String[] args) { Scanner scnr = new Scanner("8, 3.4, 1.3, 12, 4.0, 5, 6, 7, 1, 2"); scnr.useDelimiter("[, .]+"); while(scnr.hasNext()) { try { System.out.println(scnr.nextInt()/scnr.nextInt()); }catch(InputMismatchException e) { scnr.next(); continue; }catch(Exception e) { System.out.println("Something went wrong!"); System.exit(1); }finally { System.out.println("Finished!"); } } } } 6.2 Answer 2 Finished! 4 Finished! 0 Finished! Something went wrong! 7-Predict the outcome of the following: 7.1 Code provided interface Drawable{ void draw(String tool); } interface Drivable{ void drive(String road); } class Bike implements Drivable, Drawable{ String name; public Bike(String aName) { name = aName; } public void draw(String tool){ System.out.println("Drawing "+name+" with "+tool); } public void drive(String road){ System.out.println("Driving "+name+" on "+road); } } public class MainClass {

public static void main(String[] args){ Drawable[]items = new Drawable[] {new Bike("Ann's bike"),new Bike("Bob's bike")}; items[0].draw("pen"); ((Drivable)items[1]).drive("i75"); } } 7.2 Answer Drawing Ann’s bike with pen Driving Bob’s bile on i75 8-Given the following program and class Date, pick the correct implementation of the compareTo method from Comparable interface for class Date so that the program can successfully sort and print the dates stored in array days. Your implementation should work for any valid list of dates in the array. 8.1-Code Provided import java.util.*; class Date implements Comparable{ int month, day, year; public int compareTo(Object another){ if(another instanceof Date){ /*your code*/ } return 0; } Date(String rep, char delimiter){ month = Integer.parseInt(rep.substring(0, rep.indexOf(delimiter))); rep = rep.substring(rep.indexOf(delimiter) + 1); day = Integer.parseInt(rep.substring(0, rep.indexOf(delimiter))); year = Integer.parseInt(rep.substring(rep.indexOf(delimiter) + 1)); } public String toString(){ return month + "/" + day + "/" + year; } } public class MyClass { public static void main(String args[]) { Date[] days = new Date[] { new Date ( "2/7/2022" , '/' ) , new Date ( "1 5 2022" , ' ' ) , new Date ( "10,5,2020" , ',' ) }; Arrays.sort(days);//sorts days from earliest to oldest! for (Date d: days) System.out.println(d); } } 8.2 Answer: 1 st way : Date d = (Date)another; return year != d.year? year - d.year: month != d.month? month - d.month: day - d.day; 2 nd way: Date d = (Date)another; return 366*(year-d.y) + 31*(month-d.month)+(day-d.day); 3 rd way: Date d = (Date)another; return 372*(year-d.y) + 31*(month-d.month)+(day-d.day); 9-Predict the output: 9.1 Code provided: Souf(“%+05d”,12) 9.2 Answer + means show + if input is positive 0 means show leading zeros 5 means the number of characters or width that will be displayed d means interger output is +0012

 You cannot construct objects of an interface type. o A class can implement more than one interface o Example: public class Country implements Measurable, Named(named being another interface) o A class can only extend ( inherit from ) a single superclass. o An interface specifies the behavior that an implementing class should supply (in Java 8, an interface can now supply a default implementation). o A superclass provides some implementation that a subclass inherits. o Develop interfaces when you have code that processes objects of different classes in a common way o Children will automatically inherit any implementations or extension the parent class has  Abstract classes o An abstract class may contain instance fields, but an interface can't have instance fields that aren't final and static. o An abstract class needs to have at-least one abstract method. False o An abstract class cannot be instantiated, but any non-abstract class extending an abstract class can be instantiated. o A non-abstract class extending an abstract class needs to implement every abstract method in the abstract class. However, overriding non-abstract methods of the abstract class is optional. o Although an abstract class cannot be instantiated, but it can have constructors. o No one is allowed to instantiate from this class, mean that no one can say New something o Is a mixture of instance fields, abstract methods and no abstract methods. o The benefits is that you can extend it in other classes. o If your class is no abstract you are not allowed to store abstract methods in it. o An abstract class may contain instance fields , but an interface can't have any instance fields (variables). o An abstract class needs to have at-least one abstract method. False o An abstract method cannot be placed in a non-abstract class. o Although an abstract class cannot be instantiated, but it can have constructors. o A class extending an abstract class needs to implement every abstract method in the abstract class. However, overriding non-abstract methods of the abstract class is optional. o An abstract class cannot be instantiated, but any class extending an abstract class can be instantiated. o Example: public abstract class TwoDObject { protected String name; public abstract double getArea(); public abstract double getPerimeter(); @Override public String toString() { return "Generic 2-D object"; } public TwoDObject(String name) {

this.name = name; } } public class CircularObject extends TwoDObject{ int radius; public CircularObject(String name, int radius) { super(name); this.radius = radius; // TODO Auto-generated constructor stub } @Override public double getArea() { // TODO Auto-generated method stub return Math.PI*radius*radius; } @Override public double getPerimeter() { // TODO Auto-generated method stub return 2*Math.PI*radius; } }  File I/O using scanner and printwritter: o Reading a Text File using java.util.Scanner  Construct a File object and pass it to Scanner Constructor  Use Scanner.nextLine method to read a single line  Read lines repetitively until Scanner .hasNextLine method returns false.  Close the Scanner at the end.  If there is a problem with input file, it simply passes the exception to caller:  Example: public void readFile(String filename) throws IOException‚{ File inFile = new File(filename); Scanner in = new Scanner(inFile); for (int i = 1; in.hasNextLine();i++){ System.out.println("line " + i + " : " + in.nextLine()); in.close(; } o Writing into Text File: java.io.PrintWriter o Pass filename (and possibly the path) to PrintWriter Constructor. o Use print method to write text into the file. o Use printIn method to write text into the file and end the text with a new line. o Use printf method to write text with specific format o Use flush method to reflect the changes on the file immediately o Close the PrintWriter at the end. o If there is a problem with output file, it simply passes the exception to caller:

0 Show leading zeroes 001.23 + Show a plus sign for positive numbers +1.23 ( Enclose negative numbers in parentheses (1.23) , Show decimal separators 12,300 ^ Convert letters to uppercase 1.23E+1 ◦ Moreover, width and precision options are available for %d, %s, %d, and %e %-4d %5.2s %06.3e Exceptions: Designing Your Own Exception Types ► You can design your own exception types - subclasses of E xce p ti on or R untim eE xception. ► Throw an I n s u f f i c i e n tF u n dsE xce p tio n when the amount to withdraw an amount from a bank account exceeds the current balance. i f (amount > balance) { th r o w new I n s u f f i c i e n t F u n d s E x c e p t i o n ( " w i t h d r a w a l o f " amount + " exceeds balance o f " + b a l a n c e ) ; } ► Make I n s u f f i c ie n tF u n d s E x c e p ti on an unchecked exception ► Programmer could have avoided it by calling get Bal anee first ► Extend Runti meExcepti on or one of its subclasses Designing Your Own Exception Types ► Supply two constructors for the class ► A constructor with no arguments ► A constructor that accepts a message string describing reason for exception pu blic class In su fficien tF u n d sE xcep tio n extends RuntimeException { p u b lic In s u ffic ie n tF u n d s E x c e p tio n O {} p u b lic In s u ffic ie n tF u n d s E x c e p tio n (S trin g message) { super(message); } } ► When the exception is caught, its message string can be retrieved ► Using the getMessage method of the Throwable class.