Optional should only be used for return values ??and is not recommended as parameters or fields. 1. Using Optional in the return value can make it clear that the result may be empty, avoid null pointers and improve readability; 2. Using Optional in parameters and fields will increase complexity and may lead to serialization problems; 3. Over-necking of Optional will make the logic more complicated, and you should be judged with if first; 4. It is recommended to use of Nullable to create Optional to deal with uncertainty about whether there is a value.
In Java development, Optional is a container class that expresses "values ??that may or may not exist". It has been a controversial feature since Java 8: using it well can improve the readability and security of the code, while using it poorly will make the logic more complicated.
The key is: Optional should be used for return values, not as parameters or fields . Next, let's see how to use it.
1. Use Optional in the return value
This is the most recommended use scenario Optional . When you write a method whose result may be empty, use Optional to explicitly tell the caller: "This result may not be".
for example:
public Optional<User> findUserById(String id) {
// ...
}The benefits of doing this are:
- Avoid null pointer exceptions when returning
null - Remind the caller to deal with "no result" situations
- You can write more concise logic in conjunction with
ifPresent(),orElse()and other methods
Common operations include:
-
isPresent()determines whether there is a value -
get()gets the value (but make sure it exists first) -
orElse(default)returns the default value if there is no value -
orElseThrow(() -> new Exception())has no value to throw exception
However, it is recommended to use get() less and map() or flatMap() more for chain processing.
2. Do not use Optional in parameters and fields
Some developers will pass Optional as a parameter into a method or as a field type of a class, which is actually a misuse.
for example:
public void setUser(Optional<User> user) { ... }Doing so not only adds unnecessary packaging/unpacking operations, but can also lead to misunderstandings. If the parameter may be null, just let it be null, no additional encapsulation is required.
In addition, JSON serialization libraries like Jackson do not support Optional fields very much, which is prone to problems.
3. Avoid overuse of Optional
Sometimes you will see code like this:
Optional.ofNullable(user).ifPresent(u -> {
Optional.ofNullable(u.getAddress()).ifPresent(addr -> {
// ...
});
}); Although this nesting method of using Optional looks very "functional", it is actually very confusing to read, so it is better to directly judge null to be clearer.
So remember:
-
Optionalis to reduce null pointers, not to replace all null judgments - In complex logic, it is more intuitive to judge if it is honest and practical.
4. Several ways to create Optional
There are three main ways to create Optional objects:
-
Optional.of(value): value cannot be null, otherwise exception will be thrown -
Optional.ofNullable(value): Allow value to be null -
Optional.empty(): Create an empty Optional
ofNullable is usually recommended, especially if you are not sure if the value exists.
Basically that's it. Optional itself is not complicated, but it is easy to fall into the misunderstanding of "using for the sake of using it" when using it. Only by mastering its scope of application can it truly exert its value.
The above is the detailed content of When and How to Use Java Optional Correctly. For more information, please follow other related articles on the PHP Chinese website!
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