如果使用Optional类执行else代码

Question

我在这里看了一个Optional类的教程 - https://www.geeksforgeeks.org/java-8-optional-class/,它有以下内容

String[] words = new String[10];
Optional<String> checkNull = Optional.ofNullable(words[5]);
if (checkNull.isPresent()) {
    String word = words[5].toLowerCase();
    System.out.print(word);
} else{
    System.out.println("word is null");
}

我试图通过ifPresent检查Optionalas 来减少行数

Optional.ofNullable(words[5]).ifPresent(a -> System.out.println(a.toLowerCase()))

但是无法进一步获得其他部分

Optional.ofNullable(words[5]).ifPresent(a -> System.out.println(a.toLowerCase())).orElse();// doesn't work```

有办法吗？

Answer 1

Java的9

Java-9 ifPresentOrElse在实现中引入了类似的东西.你可以用它作为:

Optional.ofNullable(words[5])
        .map(String::toLowerCase) // mapped here itself
        .ifPresentOrElse(System.out::println,
                () -> System.out.println("word is null"));

Java的8

使用Java-8,您应该包含一个中间Optional/ String并用作:

Optional<String> optional = Optional.ofNullable(words[5])
                                    .map(String::toLowerCase);
System.out.println(optional.isPresent() ? optional.get() : "word is null");

也可以写成:

String value = Optional.ofNullable(words[5])
                       .map(String::toLowerCase)
                       .orElse("word is null");
System.out.println(value);

或者如果您根本不想将值存储在变量中,请使用:

System.out.println(Optional.ofNullable(words[5])
                           .map(String::toLowerCase)
                           .orElse("word is null"));