Preconditions

Ahoy, me hearties! As ye embark on yer journey through the world o’ Java Guava, ye’ll come across a powerful tool known as Guava Preconditions. This handy feature allows ye to check the arguments o’ yer methods, ensuring that they meet yer expectations before the method begins execution.

In other words, Guava Preconditions are like a gatekeeper, guarding the entrance to yer method and making sure that only the right data can pass through.

So why bother with Preconditions, ye may ask? Well, imagine ye’re a pirate captain with a treasure map in hand. Ye’ve finally reached the X that marks the spot, and ye start diggin’ with yer crew. But as ye dig, ye realize that ye’ve made a mistake in readin’ the map. Ye’ve dug in the wrong spot, and all yer effort is for naught.

Now, imagine if ye had a way to check the map before ye start diggin’. Guava Preconditions are like that map-checker, preventin’ ye from diggin’ in the wrong spot and wastin’ valuable time and resources.

But enough talkin’ like a landlubber. Let’s dive into how to use Guava Preconditions to check method arguments, so ye can start guardin’ yer methods like a true pirate captain.

Examples of Preconditions in Use

To use Guava Preconditions, ye first need to import the package:

import com.google.common.base.Preconditions;

Once ye have that sorted, ye can use any o’ the methods provided by Guava Preconditions to check yer method arguments.

Let’s say ye have a method that takes in a list o’ pirate names and ye want to make sure that the list is not null or empty before ye start executin’ yer code. Ye can use the checkNotNull and checkArgument methods to check the list:

public void pillage(List<String> pirateNames) {
  Preconditions.checkNotNull(pirateNames, "The list of pirate names cannot be null");
  Preconditions.checkArgument(!pirateNames.isEmpty(), "The list of pirate names cannot be empty");
  
  // If we've made it this far, we can start pillaging with confidence!
  // ...
}

As ye can see, we’ve used checkNotNull to make sure that the list o’ pirate names is not null, and checkArgument to ensure that the list is not empty. If either o’ these conditions is not met, Guava will throw an IllegalArgumentException, preventin’ the method from executin’.

Ye can also use Guava Preconditions to check other types o’ arguments, such as integers or strings. For example, if ye have a method that takes in an integer and ye want to make sure that it’s positive, ye can use the checkArgument method like this:

public void celebrate(int numOfRumBottles) {
  Preconditions.checkArgument(numOfRumBottles > 0, "The number o' rum bottles must be positive");
  
  // If we've made it this far, we can start celebratin' with confidence!
  // ...
}

As ye can see, we’ve used checkArgument to make sure that the number o’ rum bottles is positive. If it’s not, Guava will throw an IllegalArgumentException and prevent the method from executin’.

And there ye have it, me hearties! With Guava Preconditions, ye can ensure that yer methods only accept the right kind o’ data, preventin’ any mishaps or errors along the way. Now, set sail and start guardin’ yer methods like the pirate captain ye are!

Examples of Preconditions in Use (Continued)

In addition to checking for null or empty values, Guava Preconditions can also check for invalid states or conditions. Let’s say you have a method that takes in a string parameter and you want to make sure that the string is not null, not empty, and does not contain any spaces. You can use the checkArgument method with a custom error message to enforce these conditions:

public void hoistTheColors(String pirateMotto) {
  Preconditions.checkArgument(pirateMotto != null && !pirateMotto.isEmpty() && !pirateMotto.contains(" "),
      "Pirate motto cannot be null, empty, or contain spaces");
  
  // If we've made it this far, we can hoist the colors with pride!
  // ...
}

In this example, we’ve used checkArgument with a custom condition to ensure that the pirate motto is not null, not empty, and does not contain any spaces. If any of these conditions are not met, Guava will throw an IllegalArgumentException, preventing the method from executing.

Another useful method provided by Guava Preconditions is checkState, which can be used to check for invalid states or conditions within the method itself. Let’s say you have a method that changes the status of a pirate ship, but only if the ship is currently in port. You can use checkState to enforce this condition:

public void setSail() {
  Preconditions.checkState(status == PirateShipStatus.IN_PORT, "Cannot set sail if ship is not in port");
  
  // If we've made it this far, we can set sail with confidence!
  // ...
}

In this example, we’ve used checkState to ensure that the ship is currently in port before setting sail. If the ship is not in port, Guava will throw an IllegalStateException, preventing the method from executing.

Conclusion

And there ye have it, me hearties! Guava Preconditions may be a simple tool, but they can save ye a lot of trouble down the line by ensuring that yer methods only accept the right kind of data and are executed under the right conditions. By using Guava Preconditions to check method arguments and enforce conditions, ye can write more robust and reliable code, just like a true pirate captain. Now, set sail and start guardin’ yer methods with Guava Preconditions!