Java Optional example
Optional clearly expresses intentions and reduces code noise for null judgments. 1. Optional.ofNullable is a common way to deal with null objects. For example, when taking values from maps, orElse can be used to provide default values, which makes the logic clearer and more concise; 2. Use chain calls maps to achieve nested values, safely avoid NPE, and automatically terminate if any link is null and return the default value; 3. Filter can be used for conditional filtering, and subsequent operations will continue to be performed only if the conditions are met, otherwise it will jump directly to orElse, which is suitable for lightweight business judgment; 4. It is not recommended to overuse Optional, such as basic types or simple logic, which will increase complexity. It is more appropriate to directly return null or throw exceptions in some scenarios.
Using Java Optional is actually much more useful than you think.
Many people think Optional is a "decoration" that prevents null pointers, but when you are really using it in a project, you will find that it not only makes the code clearer, but also helps you avoid many potential bugs. Let’s take a look at how to use Optional through several actual scenarios.
1. Optional.ofNullable is the most commonly used entry
Optional.ofNullable is the most common practice when dealing with objects that may be null. For example, take the value from the map:
Map<String, String> userMap = getUserMap();
String name = Optional.ofNullable(userMap.get("name"))
.orElse("default_name");The advantage of writing this way is that it is clear logic: if the key exists, use it, and if it does not exist, give a default value. The code is much simpler than judging null first and then assigning values.
Note: If you are sure that the object is not empty, you can use
Optional.of(), but if null is passed, an exception will be thrown directly, so it is safer to useofNullablemost of the time.
2. Chained calls make nested values more elegant
Sometimes we need to take out a certain attribute from an object chain, such as user.getAddress().getCity() . At this time, it is easy to cause NPE because a certain level in the middle is null.
Rewrite it with Optional:
String city = Optional.ofNullable(user)
.map(User::getAddress)
.map(Address::getCity)
.orElse("unknown"); This method avoids null layer by layer and makes the logic clearer. Each .map() takes the value "safely" down. Once any of the links are null, the entire chain will automatically terminate and eventually return the default value you specified.
3. Use filter for conditional screening to avoid redundant judgments
Optional can also be used with filter, for example, we want to check whether the username starts with "admin":
Optional<String> usernameOpt = Optional.ofNullable(getUsername());
String result = usernameOpt.filter(u -> u.startsWith("admin"))
.map(u -> "Admin User: " u)
.orElse("Not admin");The filter in this example plays a role in filtering in advance. Only when the conditions are met will the map be executed, otherwise it will jump directly to orElse. This writing method is particularly suitable for lightweight business judgments.
4. Overuse of Optional is not recommended
Although Optional is convenient, don't abuse it. For example, when a method returns a basic type (int, boolean, etc.), Java provides an exclusive Optional type such as OptionalInt , but if you simply return an int, there is no need to go around Optional.
In addition, in some scenarios, it is more appropriate to directly return null or throw exceptions. Optional is not the master key to solve all null problems.
Basically that's it. The core value of Optional is to express intentions and reduce the noise of null judgments, rather than forcibly stuffing all logic into it. If you use it skillfully, the code will be very comfortable to read.
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