Difference between Throw and Throws in Java

In Java, throw and throws are both related to exception handling, but they serve different purposes:

throw

• Purpose:

  • throw is used to explicitly throw an exception within a method or block of code.
  • It is used to indicate that a specific exception has occurred programmatically.

• Syntax:
  
  

  throw throwableInstance;

• • Here, throwableInstance is an object of type Throwable or its subclass (typically an Exception or Error).

• Usage:

  • You can use throw to throw checked exceptions, unchecked exceptions, or errors.
  • It is typically used inside a method to handle exceptional situations where normal execution cannot proceed.

• Example:
  
  

  public void withdraw(int amount) throws InsufficientFundsException {

      if (amount > balance) {

          throw new InsufficientFundsException("Not enough balance to withdraw");

      }

      // Withdraw logic

  }

throws

• Purpose:

  • throws is used in method signatures to declare that the method may throw one or more exceptions.
  • It specifies the exceptions that a method can throw, allowing the caller to handle them appropriately.

• Syntax:
  
  

  returnType methodName(parameters) throws exceptionType1, exceptionType2, ... {

      // Method body

  }

• • Here, throws exceptionType1, exceptionType2, ... declares that the method can throw exceptions of types specified.

• Usage:

  • Use throws to declare checked exceptions that a method might throw but doesn't handle itself.
  • It does not handle exceptions; it simply declares that the method might throw certain exceptions, which the caller must handle or propagate further.

• Example:
  
  

  public void readFile(String fileName) throws FileNotFoundException {

      // Code to read a file

  }

Key Differences

• throw:

  • Used to throw an exception explicitly within a method or block.
  • Specifies the actual instance of Throwable (exception or error) being thrown.
  • Used inside method bodies to handle exceptional conditions.

• throws:

  • Used in method declarations to specify the exceptions that a method may throw.
  • Lists the types of exceptions that the method might throw, allowing the caller to handle them.
  • Does not throw exceptions itself but indicates the potential for exceptions to be thrown.

Summary

• throw is used to throw an exception programmatically within a method or block.
• throws is used in method declarations to specify the types of exceptions that a method may throw.
• Both are essential for proper exception handling in Java, where throw initiates exception handling and throws declares potential exceptions that need handling in caller methods.