Exception Handling using Throw and Throws

Lecture 89:-  Exception Handling using Throw and Throws

In Java, the throw and throws keywords are used in exception handling to propagate and declare exceptions, respectively. Both keywords play a crucial role in handling exceptional situations in a program.

1. throw Keyword:

   • The throw keyword is used to explicitly throw an exception within a method or block of code.
   • When an exceptional situation arises, you can create an exception object using the new keyword and throw it using the throw keyword.
   • The thrown exception will be propagated up the call stack to find an appropriate catch block to handle it.
   • The syntax for using the throw keyword is:

     javaCopy code
     throw new ExceptionType("Error message");
     

   • Example:

     javaCopy code
     public void withdrawMoney(double amount) throws InsufficientFundsException {
         if (amount <= balance) {
             balance -= amount;
         } else {
             throw new InsufficientFundsException("Insufficient funds in the account.");
         }
     }
     

2. throws Keyword:

   • The throws keyword is used in method signatures to declare that a method may throw one or more checked exceptions.
   • When a method is declared with the throws clause, it means that the method is not handling the exception within itself, and it is passing the responsibility of handling the exception to its caller.
   • The caller of the method must either catch the declared exception(s) using try-catch blocks or declare the exception(s) in its own method signature using the throws keyword.
   • The syntax for using the throws keyword is:

     javaCopy code
     returnType methodName(parameters) throws ExceptionType1, ExceptionType2, ...
     

   • Example:

     javaCopy code
     public void readDataFromFile(String fileName) throws IOException {
         // Code to read data from the file
     }
     

Using throw and throws together in a method, you can create custom exceptions and propagate them to the calling code when certain exceptional conditions occur. The throws keyword helps in informing the caller about the potential exceptions that may be thrown from a particular method, allowing for proper handling of these exceptions at the appropriate level in the call stack.

Remember that unchecked exceptions (runtime exceptions) do not need to be declared using the throws keyword, and they can be thrown using the throw keyword without the need for explicit declaration. However, checked exceptions must be either caught using try-catch blocks or declared in the method signature using the throws keyword.

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