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This article mainly introduces "how to use Optional". In daily operation, I believe many people have doubts about how to use Optional. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubts about "how to use Optional"! Next, please follow the editor to study!

Recognize Optional and use the

To put it simply, the Opitonal class is provided by Java to solve the judgment that people usually use null null obj to judge whether the object is empty, thus causing headaches to lead to NPE (Null Pointer Exception null pointer exception). At the same time, the existence of Optional can make the code simpler, more readable and more efficient to write.

General judgment:

/ / object person / / attribute has name,age Person person=new Person (); if (null==person) {return "person is null";} return person

Use Optional:

/ / object person / / attribute has name,age Person person=new Person (); return Optional.ofNullable (person) .orElse ("person is null")

The test shows the Person code of the class (you can take a look at this if you don't understand):

Public class Person {private String name; private Integer age; public Person (String name, Integer age) {this.name = name; this.age = age;} public Person () {} public String getName () {return name;} public void setName (String name) {this.name = name } public Integer getAge () {return age;} public void setAge (Integer age) {this.age = age;}}

Next, let's learn the magic Optional class efficiently!

Optional object creation

First of all, let's open the inside of Optional to find out how many methods to create Optional objects.

Public final class Optional {private static final Optional EMPTY = new Optional (); private final T value; / / We can see that both construction squares are private to private / / indicating that we cannot new the Optional object private Optional () {this.value = null;} private Optional (T value) {this.value = Objects.requireNonNull (value) outside. } / / this static method roughly creates an object with an empty wrapper value because there is no parameter to assign public static Optional empty () {@ SuppressWarnings ("unchecked") Optional t = (Optional) EMPTY; return t } / / this static method roughly creates an object with a non-empty wrapper value because it assigns public static Optional of (T value) {return new Optional (value). } / / this static method roughly creates an empty object if the parameter value is empty, and if it is not empty, creates a parametric object public static Optional ofNullable (T value) {return value = = null? Empty (): of (value);}}

Do a simple example to show that it corresponds to the above.

/ / 1. Create an Optional object with empty wrapper object value Optional optEmpty = Optional.empty (); / 2, create Optional object with nonempty wrapper object value Optional optOf = Optional.of ("optional"); / / 3, create Optional object Optional optOfNullable1 = Optional.ofNullable (null) with or without null wrapper object value; Optional optOfNullable2 = Optional.ofNullable ("optional")

After a rough analysis of our internal methods for creating Optional objects, we formally enter into the study and use of Optional. For more technical points of Java interview, reply "aggregation of interview questions" in the official account of Java bosom friend.

The Optional.get () method (returns the value of the object)

The get () method returns the source code of an instance value of option:

Public T get () {if (value = = null) {throw new NoSuchElementException ("No value present");} return value;}

That is, if value is not empty, it will be returned. If it is empty, an exception "No value present" will be thrown to show a simple instance.

Person person=new Person (); person.setAge (2); Optional.ofNullable (person). Get ()

Optional.isPresent () method (to determine whether the reading is empty)

The isPresent () method simply returns a value of type boolean, true if the object is not empty, and false source code if it is empty:

Public Boolean isPresent () {return value! = null;}

A simple example shows:

Person person=new Person (); person.setAge (2); if (Optional.ofNullable (person). IsPresent ()) {/ / write non-empty logical System.out.println ("not empty");} else {/ / write empty logical System.out.println ("empty");}

Optional.ifPresent () method (to determine whether it is empty or not and return a function)

This means that if the object is not empty, run the function body source code:

Public void ifPresent (Consumer

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