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

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

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.