Guards in Java: Ensuring Robust Code

When writing software, it’s important to ensure that the code is robust and resilient. One way to do this is by implementing guards, which are checks that ensure that the code behaves as expected and is protected from potential errors. In Java, guards can be implemented in several ways to ensure that code is reliable and robust.

Using Assertions for Guarding

Java provides the assert statement, which can be used to check assumptions and ensure that code is behaving as expected. Assertions can be added to code to ensure that a condition is met at a particular point in the code. If the condition is not met, the assertion will throw an AssertionError, which can be caught and handled accordingly.

For example, let’s say that we’re building a calculator application and we want to ensure that the value entered by the user is not negative. We can add an assertion to ensure that the value entered is positive:

int value = /* value entered by user */;

assert value >= 0 : "Value must be positive";

In this example, if the user enters a negative value, the assertion will fail and an AssertionError will be thrown with the message "Value must be positive".

Using Exceptions for Guarding

Java also provides exceptions as a way to handle errors and ensure that code is robust. Exceptions can be thrown to indicate that an error has occurred, and can be caught and handled in a try-catch block.

For example, let’s say that we’re building a banking application and we want to ensure that a user has sufficient funds in their account before allowing a transaction. We can add a check to ensure that the user has enough funds, and throw an exception if they do not:

In this example, if the user does not have enough funds in their account, an InsufficientFundsException will be thrown with the message "User has insufficient funds".

Using Preconditions for Guarding

Preconditions are another way to guard against errors in Java. Preconditions are checks that are made at the beginning of a method or function to ensure that the inputs are valid and that the code can safely proceed. Preconditions can be implemented using various libraries, such as Google’s Guava library.

For example, let’s say that we’re building a method that calculates the factorial of a number. We can add a precondition to ensure that the input is not negative:

public int factorial(int n) {
    Preconditions.checkArgument(n >= 0, "Input must be non-negative");
    // calculate factorial
}

In this example, if a negative number is passed as input to the factorial method, a IllegalArgumentException will be thrown with the message "Input must be non-negative".

Conclusion

Guards are an important part of writing robust and resilient code in Java. Assertions, exceptions, and preconditions are all useful ways to implement guards and ensure that code is behaving as expected. By using guards effectively, we can help to prevent errors and ensure that our code is reliable and robust.