java - 使用方法引用替换链式方法调用

Question

“Java 8 Lambdas: Pragmatic Functional Programming”有一个在Stream API 中使用peek 方法的例子。这段代码打印名字以“The”开头的艺术家国籍:

Set<Nationality> nationalities = album.getMusician()
                                 .filter(artist -> artist.getName().startsWith("The"))
                                 .map(artist -> artist.getNationality())
                                 .peek(nation -> System.out.println(nation))
                                 .collect(Collectors.toList());

我想用方法引用重写这段代码:

Set<Nationality> nationalities = album.getMusician()
                                 .filter(artist -> artist.getName().startsWith("The"))
                                 .map(Artist::getNationality)
                                 .peek(System.out::println)
                                 .collect(Collectors.toList());

有没有重写filter(artist -> artist.getName().startsWith("The"))的方案？

Answer 1

您需要创建一个单独的方法，它接受一个艺术家并返回一个 boolean 值:

private boolean nameStartsWithThe(Artist a) {
    return a.getName().startsWith("The");
}

Set<Nationality> nationalities = album.getMusician()
                                 .filter(this::nameStartsWithThe)

或使用静态方法:

private static boolean nameStartsWithThe(Artist a) {
    return a.getName().startsWith("The");
}

Set<Nationality> nationalities = album.getMusician()
                                 .filter(MyClass::nameStartsWithThe)