Ellpeck/Web
1
0
Fork 0
Code Issues Pull requests Releases Activity Actions

is

Browse source
This commit is contained in:
Ellpeck 2019-10-31 14:57:28 +01:00
parent 9eec185af8
commit 7467be08a1
1 changed files with 2 additions and 0 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

2
blog/java_6.md
View file

@ -123,6 +123,8 @@ public class Main {
``` ```
As you can see, I've expanded the code from before to have a `getTrucks` method, which iterates through every vehicle we have in stock and if it finds a vehicle that is an instance of the `Truck` class, it will print out a message. As you can see, I've expanded the code from before to have a `getTrucks` method, which iterates through every vehicle we have in stock and if it finds a vehicle that is an instance of the `Truck` class, it will print out a message.
Another way to think about the `instanceof` keyword is as a weird, clunky synonym to the word "is": When asking `vehicle instanceof Truck`, we're really asking "Is this vehicle a truck?"
Now that we know which of the vehicles we have in stock are trucks, it might also be useful to know the storage capabilities of all of those trucks. However, as you can see, the `i`th vehicle we're currently inspecting is always of typ `Vehicle`, as that's what we store in the `stock` list. That means that we won't be able to access any `Truck`'s `storageArea` variable. That's what the concept of *type casting* can be used for. Now that we know which of the vehicles we have in stock are trucks, it might also be useful to know the storage capabilities of all of those trucks. However, as you can see, the `i`th vehicle we're currently inspecting is always of typ `Vehicle`, as that's what we store in the `stock` list. That means that we won't be able to access any `Truck`'s `storageArea` variable. That's what the concept of *type casting* can be used for.
If you have a variable of a certain type, but you know for a fact that it's actually an instance of a *child class* of that type, then you can change that variable to be of the child class' type instead like so: If you have a variable of a certain type, but you know for a fact that it's actually an instance of a *child class* of that type, then you can change that variable to be of the child class' type instead like so: