Using Optional class in Java8

Usage of Optional in Java8

The Optional class in Java8 is a new feature for handling values ​​that may be null. In older versions of Java, we need to use conditional judgment to avoid null pointer exceptions. In Java 8, the Optional class provides an elegant and safe way to handle possibly null values.

The Optional class is a container object, which may contain non-null values ​​or be empty. By using the Optional class, we can explicitly express the situation when a certain value is null and avoid the null pointer exception.

Below we will introduce the usage of the Optional class through specific code examples.

1. Creating Optional objects

Optional objects can be created through static methods. Commonly used methods to create Optional objects are as follows:

• Optional.empty(): Create an empty Optional object.
• Optional.of(value): Create a non-null Optional object and use value as its value.
• Optional.ofNullable(value): Create an Optional object. If value is not empty, use it as the value of the Optional object. Otherwise, create an empty Optional object.

Optional<String> emptyOptional = Optional.empty();
Optional<String> nonEmptyOptional = Optional.of("Hello World");
Optional<String> nullableOptional = Optional.ofNullable("Hello World");

2. Determine whether the Optional object contains a value

We can use the isPresent() method to determine whether the Optional object contains a value. If the Optional object contains a non-null value, the isPresent() method will return true; otherwise, it will return false.

Optional<String> optional = Optional.ofNullable("Hello World");
if (optional.isPresent()) {
    System.out.println("Optional对象包含值：" + optional.get());
} else {
    System.out.println("Optional对象为空");
}

3. Get the value of the Optional object

We can use the get() method to get the value of the Optional object. If the Optional object is empty, calling the get() method will throw a NoSuchElementException exception. Therefore, before calling the get() method, it is best to use the isPresent() method to judge.

Optional<String> optional = Optional.ofNullable("Hello World");
if (optional.isPresent()) {
    System.out.println("Optional对象包含值：" + optional.get());
} else {
    System.out.println("Optional对象为空");
}

4. Use default value

In some cases, we want to use a default value instead when the Optional object is empty. This can be achieved using the orElse() method.

Optional<String> optional = Optional.empty();
String value = optional.orElse("Default Value");
System.out.println("Optional对象的值：" + value);

5. Using lambda expressions

The concept of functional programming was introduced in Java8, and we can process the value of Optional objects through lambda expressions.

Optional<String> optional = Optional.ofNullable("Hello World");
optional.ifPresent(value -> System.out.println("Optional对象的值：" + value));

6. Perform chain operations

Optional objects support chain operations, and we can use the map() method to convert the value of the Optional object.

Optional<String> optional = Optional.ofNullable("Hello World");
optional.map(value -> value.toUpperCase())
        .ifPresent(value -> System.out.println("转换后的值：" + value));

Through the above example, we can see the usage of the Optional class in Java8. The Optional class can help us handle possibly null values ​​more elegantly and avoid the occurrence of null pointer exceptions. In actual development, reasonable use of the Optional class can improve the readability and robustness of the code.

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