in this homework i have to do a predicate method that prints a question and then waits for a question. if the user enters no, the method should return false, if the user enters yes the method should return true. I have done that ! but in this part i have problems: if the user enters another thing the program must say something like "wrong answer" and repeat the question. I can't return a string because is a boolean method and i dont know how to resolve this.
Thank you!!
import acm.program.ConsoleProgram;
public class YesNo extends ConsoleProgram{
public void run () {
String answer = readLine ("would you like instructions? ");
println (StrBoo (answer));
}
private boolean StrBoo(String answer){
if (answer.equals("yes")) {
return true;
} else if (answer.equals("no")) {
return false;
} else {
return false;
}
}
}
First StrBoo is a poor method name. I would call it getAnswer(), and use something like,
private static boolean getAnswer() {
while (true) {
String answerStr = readLine ("would you like instructions? ");
answerStr = (answerStr != null) ? answerStr.trim() : "";
if ("yes".equalsIgnoreCase(answerStr)) {
return true;
} else if ("no".equalsIgnorecase(answerStr)) {
return false;
} else {
System.out.println("Wrong answer");
}
}
return false;
}
The correct design for such kind of program is to throw an exception. Here is an example:
import acm.program.ConsoleProgram;
public class YesNo extends ConsoleProgram
{
class WrongAnswerException extends Exception
{
}
public void run ()
{
try
{
String answer = readLine("would you like instructions? ");
println(StrBoo(answer));
}
catch(WrongAnswerException e)
{
println("You have to write yes or no!")
}
}
private boolean StrBoo(String answer) throws WrongAnswerException
{
if ("yes".equals(answer))
{
return true;
}
else if ("no".equals(answer))
{
return false;
}
else
{
throw new WrongAnswerException()
}
}
}
Related
I am trying to take a 3 class program and pass a boolean for reserving a room. I have driver program, building, room programs. I set the reserve to false and I can't figure out how to print out a text statement when it's already set to true. I think I am either doing the passing of the boolean through the classes from the driver wrong or missing something. I have played with reserveRoom in building class with an if statement to see if it's already true to print a statement and no matter which way I go it doesn't work.
Any help would be appreciated.
Thank you.
From my driver program that sends the boolean to the building program
System.out.print ("Which room would you like to reserve?");
System.out.print (building);
System.out.print ("reserve: ");
reservNum = input.nextInt();
building.reserveRoom(reserve, reservNum);
From my building class.
public void reserveRoom (boolean reserve, int count)
{
//class constant
//class variables
/*****************************************************/
room [count].updateReserve(reserve);
} // end
From the room class.
public void updateReserve(boolean newReserve)
{
//class constant
//class variables
/*****************************************************/
if (newReserve == false)
{
roomAvail = true;
}
else
{
roomAvail = false;
}
} // END
Well, there is some information missing in your question, however it think you are looking for:
public void updateReserve(boolean newReserve) {
if(newReserve && !roomAvail) {
System.out.println("Sorry this room is taken")
} else {
roomAvail = !newReserve;
}
}
With whatever i could understand about your question this is what i came up with -
public class Reservation {
public static void main(String args[]) {
Building building = new Building(20);
boolean reserve= false;
System.out.println("Which room would you like to reserve?");
System.out.println(building);
System.out.println("reserve: ");
int reservNum = 2;
building.reserveRoom(reserve, reservNum);
System.out.println("Is Reserved?:"+building.getRoom(reservNum).getRoomAvail());
}
}
class Building {
Room room[];
public Building(int numOfRooms) {
room = new Room[numOfRooms];
for(int i=0; i<numOfRooms; i++) {
room[i] = new Room();
}
}
public String toString() {
return "This Building has "+room.length+"rooms";
}
public Room getRoom(int roomNum){
return room[roomNum];
}
public void reserveRoom (boolean reserve, int count)
{
//class constant
//class variables
/*****************************************************/
room [count].updateReserve(reserve);
} // end
}
class Room {
boolean roomAvail;
public boolean getRoomAvail() {
return roomAvail;
}
public void updateReserve(boolean newReserve)
{
//class constant
//class variables
/*****************************************************/
if (newReserve == false)
{
roomAvail = true;
}
else
{
roomAvail = false;
}
} // END
}
How is it possible to set an object and method in a condition? I understand that, if the animal is over 50kg it weighs too much. But how about if an animal is hangry, need Love and feel boring return the method feelingNegative()?
I don't know how to set it. But after an animal sleeps, it is hangry. A thought would be:
Animal {
if (hangry == false && needLove == false && boring == false) {
return feelingNegative();
}
}
still don't know how to set it.
public class Animal {
private boolean needLove;
private boolean hangry;
private boolean boring;
private int kg;
public boolean sleep() {
return hangry = true;
}
public boolean watchTv() {
return needLove = true;
}
public void feelingPositive() {
System.out.println("I feel good");
}
public void feelingNeutral() {
System.out.println("Someting is missing...");
}
public void feelingNegative() {
System.out.println("I need love, food and fun!");
}
public void weight(int kg) {
if(50 < kg) {
System.out.println("You ate way too much");
}else {
System.out.println("You need to eat more");
}
}
}
The methods you are calling don't return anything (they are void). Just remove the return. And use boolean negation (!) instead of == false. Like,
if (!hangry && !needLove && !boring) {
feelingNegative();
}
The Method feelingNegative() doesn't return anything (Void). So you just have to define a method that call feelingNegative() when all the conditions are satisfied.
public void myMethod ()
{
if(!hangry && !needLove && !boring)
feelingNegative();
}
I've created this method and I'm unsure why it says there's a missing return statement. do I need to change the print to a return? (it's the method at the very bottom) I'm a bit of a Java beginner so any help will be appreciated!
public class Book {
private String title;
private String author;
private int copies;
private boolean borrowed;
public Book( String inAuthor, String inTitle, int inNumberOfCopies ) {
this.author = inAuthor;
this.title = inAuthor;
this.copies = inNumberOfCopies;
}
public void borrowed() {
borrowed = true;
}
public void rented() {
borrowed = true;
}
public void returned() {
borrowed = false;
}
public boolean isBorrowed() {
return borrowed;
}
public String getAuthor() {
return this.author;
}
public static String getTitle() {
return getTitle();
}
public int getTotalCopies() {
return this.copies;
}
public int getAvailableCopies() {
}
public void withdrawCopy() {
int found = 0;
for (Book b : Library.getListOfBooks()) {
if (b.getTitle().equals(title)) {
if (found == 0) {
found = 1;
}
if (!b.isBorrowed()) {
b.borrowed=true;
found = 2;
break;
}
if (found == 0) {
System.out.println("Sorry, this book is not in our catalog.");
} else if (found == 1) {
System.out.println("Sorry, this book is already borrowed.");
} else if (found == 2) {
System.out.println("You successfully borrowed " + title);
}
}
}
}
public String returnCopy() {
boolean found = false;
for (Book book : Library.getListOfBooks()) {
if (getTitle().equals(title) && book.isBorrowed()) {
book.returned();
found = true;
}
if (found) {
System.out.println("you successfully returned " + title);
}
}
}
}
public String returnCopy()
String after public means that this method will return a String.
Your public String returnCopy() is currently not returning anything.
If you don't want to return anything, you can use void like this:
public void returnCopy(){
// code
}
Same issue with public int getAvailableCopies(), this is supposed to return an int but you are not returning anything.
Be careful:
this method:
public static String getTitle() {
return getTitle();
}
is a recursive method without a base condition. This will cause an error and force your application to crash.
You've defined the method as returning a String but you don't return a value anywhere in the method body. Simplest fix is probably to change the return type to void...
public void returnCopy() {...
}
All the above answer are pointing to the same issue, you have defined methods that are breaking the contract about what they return..
In you code you have as well something like this:
public int getAvailableCopies() {
}
so you are telling the compiler, you have a method with the name getAvailableCopies, it takes no params and return an integer.
BUT if you don't return anything, then you are contradicting your own method, your own contract, this is an enough reason for a compiler to complain...
Conclusion:
keep in mind the information that defines the method.
I currently have two classes Main and Command.
They are both inside of the package emerica.simple
So the classpath is emerica.simple.Main and emerica.simple.Command
In main I define a Boolean called spyblock
public class Main extends JavaPlugin{
public static boolean spyblock = true;
In command I am trying to access it and change it
public class Command implements CommandExecutor {
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
return true;
if (Main.spyblock == true) {
Main.spyblock = false;
}
else {
Main.spyblock = true;
}
}
else
{
return false;
}
}
Hoe can I change this code so it works? I am trying to toggle main.spyblock this the command "Spyblocks"
Your code for altering spyblock is not reachable because of
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
**return true;**
if (Main.spyblock == true) {
Main.spyblock = false;
}
else {
Main.spyblock = true;
}
}
highlighted line. just move this like
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
if (Main.spyblock == true) {
Main.spyblock = false;
}
else {
Main.spyblock = true;
}
**return true;**
}
Hope this helps
You have unreachable code :
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
return true;
//unreachable code
if (Main.spyblock == true) {
Main.spyblock = false;
}
else {
Main.spyblock = true;
}
}
That's why value of Main.spyblock doesn't change.
You returned your method just above your 2nd if i.e. return true;, that's why your if is not executing, you have to put return true; after your 2nd if-else condition.
If you just want to toggle it do it like this:
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
Main.spyblock = !Main.spyblock;
}
I don't fully understsand what you are trying to do, but currently your code won't compile properly.
Try changing it to the following
public class Command implements CommandExecutor {
public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
if (cmd.getName().equalsIgnoreCase("spyblocks")) {
if (Main.spyblock == true) {
Main.spyblock = false;
}
else {
Main.spyblock = true;
}
return true;
}
return false;
}
You can also change your logic, making it a bit simpler, since you do not have to check for both conditions, since you are always toggling it. Therefore just always set it to the opposite of what it currently is.
Main.spyblock = !Main.spyblock;
I'm trying to implement this automaton example : http://www.javacodegeeks.com/2012/03/automaton-implementation-in-java.html.
However, an error keeps on being displayed while running the program :
Exception in thread "main" java.lang.StringIndexOutOfBoundsException:
String index out of range: 3
at java.lang.String.charAt(String.java:686)
at mealy.Input.read(Input.java:7)
at mealy.States$4.next(Input.java:46)
at mealy.Test.main(Test.java:9)
I tried modifying the lines responsible for the error but nothing changed. Could someone please take a look at this program and help me find a solution?
I have the following .java :
State.java :
interface State {
public State next(Input in);
}
NB : I had to change the original "public Stat next()" into "public State next(Input in);"
Input.java :
class Input {
private String input;
private int current;
public Input(String input) {this.input = input;}
char read() { return input.charAt(current++); }
}
enum States implements State {
Init {
#Override
public State next(Input word) {
switch(word.read()) {
case 'a': return A;
default: return Fail;
}
}
},
A {
#Override
public State next(Input word) {
switch(word.read()) {
case 'a': return A;
case 'b': return B;
case 'c': return C;
case 'd': return null;
default: return Fail;
}
}
},
B {
#Override
public State next(Input word) {
switch(word.read()) {
case 'b': return B;
case 'c': return C;
case 'd': return null;
default: return Fail;
}
}
},
C {
#Override
public State next(Input word) {
switch(word.read()) {
case 'c': return C;
case 'd': return null;
default: return Fail;
}
}
},
Fail {
#Override
public State next(Input word) {
return Fail;
}
};
public abstract State next(Input word);
}
Test.java :
public class Test {
public static void main(String args[]){
State s;
Input in = new Input("abc");
for(s = States.Init; s != null || s != States.Fail; s = s.next(in)) {}
if(s == States.Init) {System.out.println("Valid!");}
else {System.out.println("Failed");}
}
}
There appears to be a bug in the Input class. When you attempt to read the character after the last one, it throws an exception you are not handling in main. I would change Input so that it return a token you can handle in your state machine.
BTW I suggest you have a look at this for context. http://vanillajava.blogspot.co.uk/2011/06/java-secret-using-enum-as-state-machine.html
I assume Attila was looking to provide a simple, working example. I will see if he can fix his code.
you need to change read() method like below
char read() {
if(current>=input.length()) // this if condition should be checked
return 'z'; // you need to change your character according to your need
return input.charAt(current++);
}
the error is in this line
char read() { return input.charAt(current++); }
You don't check the length of the String input (which i consider a bad name inside a class Input) and after calling read() three times you try to access the 4th letter of a 3 letter String, which then throws the exception you see.
Update:
Addressing your comment I'd suggest changing the return value of read() to a new interface ReadResult:
public interface ReadResult {
boolean isOkay();
char getReadCharacter();
}
with two implementations. one for positive results...
public class ReadOkay implements ReadResult{
private char readCharacter;
public ReadOkay(char readCharacter) {
this.readCharacter = readCharacter;
}
#Override
public boolean isOkay() {
return true;
}
#Override
public char getReadCharacter() {
return readCharacter;
}
}
and one for negative results
public class ReadFailed implements ReadResult {
#Override
public boolean isOkay() {
return false;
}
#Override
public char getReadCharacter() {
throw new IllegalStateException("Read failed! no character data there to return!");
}
}
Having this you can change read() to let it return then new interface
public ReadResult read() {
if (input != null && current >= 0 && current < input.length()) {
return new ReadOkay(input.charAt(current++));
} else {
return new ReadFailed();
}
}
and update your States accordingly.
replace:
switch(word.read()) {
with:
ReadResult result = word.read();
if (!result.isOkay()) {
return Fail;
}
switch (result.getReadCharacter()) {