过滤流不同

Question

java prettyprint-override">class Developer{
    private Long id;
    private String name;
    private Integer codePost;
    private Integer codeLevel;
}

null

或用java

Developer dev1 = new Developer (1,"Alan stonly",30,4);
Developer dev2 = new Developer (2,"Peter Zola",20,4);
Developer dev3 = new Developer (3,"Camilia Frim ",30,5);
Developer dev4 = new Developer (4,"Antonio Alcant",40,4);

Stream<Developer> Developers = Stream.of(dev1, dev2, dev3 , dev4);

Answer 1

正如注释中提到的，collectors.tomap应该在这里与合并函数一起使用（还可以选择映射供应商，例如LinkedHashMap::new，以保持插入顺序）：

java prettyprint-override">Stream.of(dev1, dev2, dev3, dev4)
    .collect(Collectors.toMap(
        Developer::getCodePost,
        dev -> dev,
        (d1, d2) -> Stream.of(d1, d2)
                          .filter(d -> d.getCodeLevel() == 5)
                          .findFirst()
                          .orElse(d1),
        LinkedHashMap::new // keep insertion order
    ))
    .values()
    .forEach(System.out::println);

merge函数也可以用三进制运算符实现：

(d1, d2) -> d1.getCodeLevel() == 5 ? d1 : d2.codeLevel() == 5 ? d2 : d1

产出：

Developer(id=3, name=Camilia Frim , codePost=30, codeLevel=5)
Developer(id=2, name=Peter Zola, codePost=20, codeLevel=4)
Developer(id=4, name=Antonio Alcant, codePost=40, codeLevel=4)