Why is throws Exception necessary when calling a function

Question

class throwseg1       void show   throws Exception               throw new Exception  my own Exception               void show2   throws Exception     Why throws is necessary here                 show               void show3   throws Exception     Why throws is necessary here                 show2               public static void main String s    throws Exception     Why throws is necessary here                 throwseg1 o1   new throwseg1            o1 show3              Why compiler reports that methods show2    show3    and main   have      unreported exception Exception that must be caught or declared to be thrown   when I remove throws Exception from these methods

User · Answer

Java requires that you handle or declare all exceptions. If you are not handling an Exception using a try/catch block then it must be declared in the method's signature.

For example:

class throwseg1 {
    void show() throws Exception {
        throw new Exception();
    }
}

Should be written as:

class throwseg1 {
    void show() {
        try {
            throw new Exception();
        } catch(Exception e) {
            // code to handle the exception
        }
    }
}

This way you can get rid of the "throws Exception" declaration in the method declaration.

User · Answer

The throws Exception declaration is an automated way of keeping track of methods that might throw an exception for anticipated but unavoidable reasons   The declaration is typically specific about the type or types of exceptions that may be thrown such as throws IOException or throws IOException  MyException   We all have or will eventually write code that stops unexpectedly and reports an exception due to something we did not anticipate before running the program  like division by zero or index out of bounds   Since the errors were not expected by the method  they could not be  caught  and handled with a try catch clause   Any unsuspecting users of the method would also not know of this possibility and their programs would also stop   When the programmer knows certain types of errors may occur but would like to handle these exceptions outside of the method  the method can  throw  one or more types of exceptions to the calling method instead of handling them   If the programmer did not declare that the method  might  throw an exception  or if Java did not have the ability to declare it   the compiler could not know and it would be up to the future user of the method to know about  catch and handle any exceptions the method might throw  Since programs can have many layers of methods written by many different programs  it becomes difficult  impossible  to keep track of which methods might throw exceptions     Even though Java has the ability to declare exceptions  you can still write a new method with unhandled and undeclared exceptions  and Java will compile it and you can run it and hope for the best  What Java won t let you do is compile your new method if it uses a method that has been declared as throwing exception s   unless you either handle the declared exception s  in your method or declare your method as throwing the same exception s  or  if there are multiple exceptions  you can handle some and throw the rest    When a programmer declares that the method throws a specific type of exception  it is just an automated way of warning other programmers using the method that an exception is possible   The programmer can then decide to handled the exception or pass on the warning by declaring the calling method as also throwing the same exception   Since the compiler has been warned the exception is possible in this new method  it can automatically check if future callers of the new method handle the exception or declare it and enforcing one or the other to happen   The nice thing about this type of solution is that when the compiler reports Error  Unhandled exception type java io IOException it gives the file and line number of the method that was declared to throw the exception   You can then choose to simply pass the buck and declare your method also  throws IOException    This can be done all the way up to main method where it would then cause the program to stop and report the exception to the user   However  it is better to catch the exception and deal with it in a nice way such as explaining to the user what has happened and how to fix it   When a method does catch and handle the exception  it no longer has to declare the exception   The buck stops there so to speak

User · Answer

Basically  if you are not handling the exception in the same place as you are throwing it  then you can use  throws exception  at the definition of the function

User · Answer

If you propagate the exception by declaring the throws directive in the signature of the current method  then somewhere up the line or call stack a try catch construct must be used to handle the exception

User · Answer

void show   throws Exception       throw new Exception  my own Exception        As there is checked exception in show   method   which is not being handled in that method so we use throws keyword for propagating the Exception   void show2   throws Exception   Why throws is necessary here     show        Since you are using the show   method in show2   method and you have propagated the exception atleast you should be handling here  If you are not handling the Exception here   then you are using throws keyword  So that is the reason for using throws keyword at the method signature

User · Answer

In Java  as you may know  exceptions can be categorized into two  One that needs the throws clause or must be handled if you don t specify one and another one that doesn t  Now  see the following figure     In Java  you can throw anything that extends the Throwable class  However  you don t need to specify a throws clause for all classes  Specifically  classes that are either an Error or RuntimeException or any of the subclasses of these two  In your case Exception is not a subclass of an Error or RuntimeException  So  it is a checked exception and must be specified in the throws clause  if you don t handle that particular exception  That is why you needed the throws clause     From Java Tutorial      An exception is an event  which occurs during the execution of a program  that disrupts the normal flow of the program s instructions    Now  as you know exceptions are classified into two  checked and unchecked  Why these classification   Checked Exception  They are used to represent problems that can be recovered during the execution of the program  They usually are not the programmer s fault  For example  a file specified by user is not readable  or no network connection available  etc   In all these cases  our program doesn t need to exit  instead it can take actions like alerting the user  or go into a fallback mechanism like offline working when network not available   etc   Unchecked Exceptions  They again can be divided into two  Errors and RuntimeExceptions  One reason for them to be unchecked is that they are numerous in number  and required to handle all of them will clutter our program and reduce its clarity  The other reason is    Runtime Exceptions  They usually happen due to a fault by the programmer  For example  if an ArithmeticException of division by zero occurs or an ArrayIndexOutOfBoundsException occurs  it is because we are not careful enough in our coding  They happen usually because some errors in our program logic  So  they must be cleared before our program enters into production mode  They are unchecked in the sense that  our program must fail when it occurs  so that we programmers can resolve it at the time of development and testing itself  Errors  Errors are situations from which usually the program cannot recover  For example  if a StackOverflowError occurs  our program cannot do much  such as increase the size of program s function calling stack  Or if an OutOfMemoryError occurs  we cannot do much to increase the amount of RAM available to our program  In such cases  it is better to exit the program  That is why they are made unchecked    For detailed information see     Unchecked Exceptions     The Controversy The Catch or Specify Requirement

User · Answer

package javaexception    public class JavaException      void show   throws Exception               throw new Exception  my own Exception           void show2   throws Exception     Why throws is necessary here         show       void show3   throws Exception     Why throws is necessary here         show2      public static void main String   args        JavaException a   new JavaException        try     a show3        catch Exception e          System out println e getMessage              Only small changes in your program  What It seems to be misunderstood by many regarding the main issue  is whenever you throw exception you need to handle it  not necessary in the same place   ex  show1 2 3 method in your program  but you must at first caller method inside the  main   in one word  there is  throw   there must be  catch try   even if not same method where exception happens

User · Answer

Exception is a checked exception class  Therefore  any code that calls a method that declares that it throws Exception must handle or declare it

[java] Why is "throws Exception" necessary when calling a function?

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