Java throw exception if statement
Exceptions (all classes that subclass the Exception class) can be caught. So you would need to catch exceptions like Solution 3: You could just print to the console and exit Java (instead of throwing an exception), as that is what an Exception does in essence.
Multiple Exception Handling in one if statement
I am having trouble with throwing and catching exceptions.
Here is the code for assignSeat(), assignSeat is called in a try block in another class.
void assignSeat(String passengerName, int x, int y) throws SeatOccupiedException, InvalidPassengerNameException < Seat tSeat = airplane.getSeat(x,y); if (tSeat!=null) < if (passengerName.isEmpty() || !passengerName.matches("[a-zA-Z]+")) < throw new InvalidPassengerNameException(); >//excluded else if else if (foundPassenger(passengerName)) < airplane.seatList.get(airplane.seatNumber(passengerName)).unOccupy(); tSeat.occupy(); for (int i = 0; ielse if (!tSeat.occupied) < tSeat.occupy(); addPassenger(passengerName, tSeat.getSeatName()); >else if (tSeat.occupied) < throw new SeatOccupiedException(); >> and here is the code that calls assignSeat() and is in another class (I won’t copy the whole class to make it look clearer)
if (afComp.currentAF != null) < try < afComp.currentAF.assignSeat(nameField.getText(), x, y); //catch (SeatOccupiedException exception) // catch(InvalidPassengerNameException exception) // > Whats wrong with the try block? why won’t it throw the SeatOccupiedException?
package a2; public class SeatOccupiedException extends Exception < public SeatOccupiedException()<>> package a2; public class InvalidPassengerNameException extends Exception < public InvalidPassengerNameException() <>> Every class I have is in package a2
imports for class that calls assignSeat
package a2; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.MouseListener; import java.awt.event.MouseMotionListener; import java.awt.event.MouseEvent; import java.awt.BorderLayout; import javax.swing.*; import javax.swing.event.*; imports for class that has assignSeat
package a2; import java.util.ArrayList; Most probably, you have two SeatOccupiedException classes in two different packages, your method throws the class from one package while your code catches the other class.
Change the logic and simplify your statement:
if ( tSeat.occupied ) < throw new SeatOccupiedException(); >if ( /* bad passenger name */ ) < throw new InvalidPassengerNameException(); >if ( /* passenger does not exist */ ) < throw new PassengerNotFoundException(); >/* assign Seat here */ Throw new exception in Ternary condition [duplicate], You can’t throw an exception in a ternary clause. Both options must return a value, which throw new Exception(); doesn’t satisfy.
JavaScript Question: Should I Use try catch or an if Conditional?
Try catch is great for exception handling. But it is possible to use an if conditional in certain Duration: 7:02
Error handling with if statement
This is to validate my GUI input and make sure the user can not enter values out of range
I’m trying to handle this Exception with if statement but I’m still printing the red error message. I just want the «Value out of range» message to be printed. I don’t want those red exceptions error in my console. Please help or advise. Any other way to handle this can is fine with me.
if (totalTimeToTakeOff 1 || departureRate < 0 || departureRate >1 || remaingFuel
Well what you are doing here is creating a new IllegalArgumentException object, and then this method throws this exception. When you throw an exception, the part of your code that calls this method has to handle that exception OR those ‘red lines’ (the stack trace, basically) are printed. So, for a simple example, say that you have the method divide()
public double divide(double a, double b) < if(b==0)< throw new IllegalArgumentException("Divisor cannot be 0"); >return a/b; > Now, when some other part of your code calls this method, you can choose to handle the IllegalArgumentException that is thrown by this method.
try< double c = divide(a,b); >catch(IllegalArgumentException e) < //put whatever code you want here > If you don’t catch the exception, then your code breaks and the stack trace (the red text) is printed out. So in other words, your code is functioning as intended; that section of code throws an IllegalArgumentException under some circumstance, and the code that calls that method does not catch the exception and handle it (for example by printing out the message about the exception).
Also, just a minor note- an error in java is different from an exception. An error signifies a process from which the program cannot recover, and an error cannot be caught. Exceptions (all classes that subclass the Exception class) can be caught. An exception can either be checked or unchecked — checked exceptions MUST be caught via a catch statement, whereas unchecked exceptions don’t. An example of a checked exception is the IOException, whereas an example of an unchecked exception is the IllegalArgumentException you have displayed here.
One more thing- exceptions are meant to signify an abnormality in your code. If this IllegalArgumentException was thrown from say, a class constructor or a method that can be used for many general purposes, then it makes sense to throw it. However, if that method exists solely for the purpose of checking whether input is valid, then have it return a boolean value (true or false) rather than throwing an exception.
One other reason to this is because exception handling tends to be rather slow in comparison to simply returning a true or a false.
You need to understand this please look into it.
There is also an finally block which will always be execute even if there is an error. it is used like this
try < //Something that can throw an exception. >catch (Exception e) < // To do whatever when the exception is caught & the returned. >finally < // This will always execute if there is an exception or no exception. >InputMismatchException — if the next token does not match the Integer regular expression, or is out of range NoSuchElementException — if input is exhausted IllegalStateException — if this scanner is closed
So you would need to catch exceptions like
try < rows=scan.nextInt(); >catch (InputMismatchException e) < // When the InputMismatchException is caught. System.out.println("The next token does not match the Integer regular expression, or is out of range"); >catch (NoSuchElementException e) < // When the NoSuchElementException is caught. System.out.println("Input is exhausted"); >catch (IllegalStateException e) < // When the IllegalStateException is caught. System.out.println("Scanner is close"); >You could just print to the console and exit java (instead of throwing an exception), as that is what an Exception does in essence.
System.out.println("Values out of range"); System.exit(0); Alternatively, catch the exception when calling the method
you could check the values without throwing an exception
if (!checkValues()) System.out.println("Values out of range"); Using an else-if statement with in a try-catch-finally, I am trying to use a try-catch-finally statement to error check user input and then advance to the next page if there are no error (I know
Can exception be perfectly replaced by if.. else?
I’m new to programming and I have a conceptual question.
That is, can «exception» be perfectly replaced by «if.. else» ?
I know «exception» is to handling some exceptional conditions that might cause error or crash.
But we also use «if.. else» to ensure the correctness of value of variables, don’t we?
Or «exception» can really be replaced by «if.. else», but using «exception» has other benefits(like convenience?)
Thank you, and sorry for my poor English.
The biggest difference between exceptions and «if..else» is that exceptions pass up the call stack: an exception raised in one function can be caught in a caller any number of frames up the stack. Using «if» statements doesn’t let you transfer control in this way, everything has to be handled in the same function that detected the condition.
Technically, the answer is yes, exceptions can be perfectly replaced by if-else. Many languages, C for example, have no native notion of exceptions that can be thrown and caught.
The primary advantage of exceptions is code readability and maintainability. They serve a different purpose than if-else. Exceptions are for exceptional conditions, while if-else is for program flow.
See this excellent article explaining the difference.
Most of your questions relate to Python, so here is an answer based on that fact.
In Python, it is idiomatic (or «pythonic») to use try — except blocks. We call this «EAFP»: easier to ask for forgiveness than permission.
In C, where there were no exceptions, it was usual to «LBYL»: Look before you leap, resulting in lots of if (. ) statements.
So, while you can LBYL, you should follow the idioms of the language in which you are programming: using exceptions for handling exceptional cases and if -statements for conditionals.
That’s a lot of branch conditions to manage. In theory, exceptions aren’t necessary for perfect code, but perfect code does not exist in real life. Exceptions are a well-established mechanism for dealing with problems in a controlled manner.
Difference between try-catch and if-else statements in PHP, Use one block to handle errors or exception: In case of if-else we have one else block corresponding to one if block, so we have to define each