Difference Between 'throw' and 'throws' in Java Exception Handling

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Question:

What is the difference between the ‘throw' and ‘throws' keyword in Java?

Answer:

In Java, throw and throws are both related to exception handling, but they serve different purposes and are used in different contexts. Here’s a breakdown of the differences:

throw

  • Purpose: The throw keyword is used to explicitly throw an exception from a method or a block of code.
  • Usage: You can use throw to create an instance of an exception class and throw it. This is typically done when a certain condition is met that warrants an exception.
  • Example:
    public void checkAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Age must be at least 18");
        }
    }
    

throws

  • Purpose: The throws keyword is used in a method declaration to indicate that the method can throw one or more exceptions. It informs the caller of the method that they need to handle these exceptions.
  • Usage: You use throws in the method signature to declare that the method may throw specific checked exceptions.
  • Example:
    public void readFile(String filePath) throws IOException {
        FileReader file = new FileReader(filePath);
        BufferedReader br = new BufferedReader(file);
        // Code to read the file
    }
    

Summary

  • throw: Used to actually throw an exception.
  • throws: Used in a method signature to declare that the method may throw exceptions, allowing the caller to handle them.

Key Points

  • You can throw both checked and unchecked exceptions using throw.
  • When using throws, you can only declare checked exceptions (those that are subclasses of Exception, but not RuntimeException).
  • A method can have multiple exceptions declared with throws, separated by commas.

Understanding the distinction between these two keywords is crucial for effective exception handling in Java.