What's the purpose of partitioningBy

Question

For example, if I intend to partition some elements, I could do something like:

Stream.of(\"I\", \"Love\", \"Stack Overflow\")
      .collect(Collectors.part         


        

Answer 1

As denoted by the other answers, segregating a collection into two groups is useful in some scenarios. As these two partitions would always exist, it would be easier to utilize it further. In JDK, to segregate all the class files and config files, partitioningBy is used.

    private static final String SERVICES_PREFIX = "META-INF/services/";
    
    // scan the names of the entries in the JAR file
    Map> map = jf.versionedStream()
            .filter(e -> !e.isDirectory())
            .map(JarEntry::getName)
            .filter(e -> (e.endsWith(".class") ^ e.startsWith(SERVICES_PREFIX)))
            .collect(Collectors.partitioningBy(e -> e.startsWith(SERVICES_PREFIX),
                                               Collectors.toSet()));

    Set classFiles = map.get(Boolean.FALSE);
    Set configFiles = map.get(Boolean.TRUE);

Code snippet is from jdk.internal.module.ModulePath#deriveModuleDescriptor