1、of方法用于创建一个非空Optional对象。如果参数为null，则抛出NullPointerException异常。

        Optional<String> optionalStr = Optional.of("Hello World");System.out.println(optionalStr); // Optional[Hello World]Optional<String> optionalStr1 = Optional.of("null");System.out.println(optionalStr1); // Optional[null]// 如果参数为null，则抛出NullPointerException异常。//Optional<String> optionalStr2 = Optional.of(null);//System.out.println(optionalStr2);

2、ofNullable方法用于创建一个可能为空的Optional对象.

    String str = null;Optional<String> optionalStr3 = Optional.ofNullable(str);System.out.println(optionalStr3); // Optional.emptySystem.out.println(Optional.empty()); // Optional.empty

3、isPresent方法返回一个布尔值，表示Optional对象中是否包含非空值。

    Optional<String> optionalStr4 = Optional.ofNullable("Hello World");if (optionalStr4.isPresent()) {System.out.println("The value is present.");} else {System.out.println("The value is absent.");} // The value is present.Optional<String> optionalStr5 = Optional.empty();if (optionalStr5.isPresent()) {System.out.println("The value is present.");} else {System.out.println("The value is absent.");} // The value is absent.

4、get方法返回Optional对象中的值。如果Optional对象为空，则抛出NoSuchElementException异常。

    Optional<String> optionalStr6 = Optional.ofNullable("Hello World");String str6 = optionalStr6.get();System.out.println(str6); // Hello WorldOptional<String> optionalStr7 = Optional.empty();//String str7 = optionalStr7.get(); // Exception in thread "main" java.util.NoSuchElementException: No value present//System.out.println(str7);

5、orElse方法在Optional对象为空时提供备选值.

    Optional<String> optionalStr8 = Optional.empty();String str8 = optionalStr8.orElse("Default Message");System.out.println(str8); // Default MessageOptional<String> optionalStr9 = Optional.ofNullable("Hello World");String str9 = optionalStr9.orElse("Default Message");System.out.println(str9); // Hello World

6、ifPresent方法允许在Optional对象中存在非空值时执行一些操作。

    Optional<String> optionalStr10 = Optional.ofNullable("Hello World");optionalStr10.ifPresent(str0 -> System.out.println("The value is present: " + str0)); // The value is present: Hello WorldOptional<String> optionalStr11 = Optional.empty();optionalStr11.ifPresent(str0 -> System.out.println("The value is present: " + str0)); //

7、filter方法允许过滤Optional对象中的值。如果值满足Predicate函数式接口所定义的条件，则返回一个包含该值的Optional对象；否则返回空的Optional对象.

    Optional<String> optionalStr12 = Optional.ofNullable("Hello World");Optional<String> filtered12 = optionalStr12.filter(str0 -> str0.contains("World"));if (filtered12.isPresent()) {System.out.println(filtered12.get()); // Hello World} else {System.out.println("The value does not contain 'World'.");}Optional<String> optionalStr13 = Optional.empty();Optional<String> filtered13 = optionalStr13.filter(str0 -> str0.contains("World"));if (filtered13.isPresent()) {System.out.println(filtered13.get());} else {System.out.println("The value does not contain 'World'."); // The value does not contain 'World'.}

8、map方法允许将Optional对象中的值转换为另一种类型并返回一个包含新值的Optional对象。

    Optional<String> optionalStr14 = Optional.ofNullable("Hello World");Optional<Integer> length14 = optionalStr14.map(String::length);System.out.println(length14.get()); // 11Optional<String> optionalStr15 = Optional.empty();// Optional<Integer> length15 = optionalStr15.map(String::length);// System.out.println(length15.get()); // Exception in thread "main" java.util.NoSuchElementException: No value present

9、flatMap方法与map方法类似，但它接受一个返回Optional对象的Function函数式接口作为参数，并将其返回值作为最终结果。可以在Optional对象上执行更复杂的操作。

    Optional<String> optionalStr16 = Optional.ofNullable("Hello World");Optional<Character> firstChar16 = optionalStr16.flatMap(str0 -> Optional.ofNullable(str0.charAt(0)));System.out.println(firstChar16.get()); // HOptional<String> optionalStr17 = Optional.empty();//Optional<Character> firstChar17 = optionalStr17.flatMap(str0 -> Optional.ofNullable(str0.charAt(0)));//System.out.println(firstChar17.get()); // Exception in thread "main" java.util.NoSuchElementException: No value present

10、orElseGet方法与orElse方法类似，但它接受一个Supplier函数式接口作为参数，该接口定义了在Optional对象为空时提供备选值的逻辑。

    Optional<String> optionalStr18 = Optional.ofNullable(null);String str18 = optionalStr18.orElseGet(() -> "Default Message");System.out.println(str18); // Default Message// orElseGet方法与orElse方法类似，但它接受一个Supplier函数式接口作为参数，该接口定义了在Optional对象为空时提供备选值的逻辑。Optional<String> optionalStr19 = Optional.ofNullable(null);String str19 = optionalStr19.orElseGet(() -> "Default Message");System.out.println(str19); // Default Message

11、orElseThrow方法在Optional对象为空时抛出指定类型的异常.

Optional<String> optionalStr20 = Optional.ofNullable(null);String str20 = optionalStr20.orElseThrow(() -> new RuntimeException("Value is null")); // Exception in thread "main" java.lang.RuntimeException: Value is null