java - Java 8 中从 Map 到 List 属性的过滤键

Question

我有一个列表和一个 map 如下:

public class student {
private String name;
private String age;
private String id;
public String getName() {
    return name;
}
public void setName(String name) {
    this.name = name;
}
public String getAge() {
    return age;
}
public void setAge(String age) {
    this.age = age;
}
public String getId() {
    return id;
}
public void setId(String id) {
    this.id = id;
}
student(String id,String name,String age)
{
    }
}
List<student> stulist = Arrays.asList(new student("1", "vishwa",null),
                                              new student("3", "Ravi",null),
                                              new student("2", "Ram",null));

Map<String,String> newmap = new HashMap() {
                                               {
                                                   put("1","20");
                                                   put("2","30");
                                                   }
                                        };

I am comparing like this: If id in map matches the id in list then add age from Map to age of List.

到目前为止我已经试过了，但是我无法得到它。

newmap.entrySet().stream().filter(entry->entry.getKey().equals(student::getId)).collect(..collect here to list..);

Answer 1

stulist = stulist.stream().map(instance -> {
    student studentInstance = instance; 
    studentInstance.setAge(newMap.getOrDefault(studentInstance.getId(),"<default age>"));
    return studentInstance;
}).collect(Collectors.toList()); ;

ps:使用正确的命名约定。将类(class)名称 student 更改为 Student。