类型推断不适用于Eclipse Luna

Question

我刚刚开始使用Java 8，我正在尝试收集器上的一些示例。我跟着这本书，Java 8在行动。我对类型推断有疑问：

我使用了基本模型类Student，Name来创建示例。 PFB详情：

package com.learning.fundamentals;

import java.util.ArrayList;
import java.util.List;

public class Student {
    public enum Gender {
        MALE, FEMALE;
    }
    private String id;
    private Name name;
    private Gender gender;
    public Student(String id, Name name, Gender gender) {
        this.id = id;
        this.name = name;
        this.gender = gender;
    }
    public String getId() {
        return id;
    }
    public Name getName() {
        return name;
    }
    public Gender getGender() {
        return gender;
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((gender == null) ? 0 : gender.hashCode());
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Student other = (Student) obj;
        if (gender != other.gender)
            return false;
        if (id == null) {
            if (other.id != null)
                return false;
        } else if (!id.equals(other.id))
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }
    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", gender=" + gender
                + "]";
    }

}

package com.learning.fundamentals;

public class Name {
    private String firstName;
    private String middleName;
    private String lastName;
    public Name(String firstName, String middleName, String lastName) {
        this.firstName = firstName;
        this.middleName = middleName;
        this.lastName = lastName;
    }
    public String getFirstName() {
        return firstName;
    }
    public String getMiddleName() {
        return middleName;
    }
    public String getLastName() {
        return lastName;
    }
    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result
                + ((firstName == null) ? 0 : firstName.hashCode());
        result = prime * result
                + ((lastName == null) ? 0 : lastName.hashCode());
        result = prime * result
                + ((middleName == null) ? 0 : middleName.hashCode());
        return result;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Name other = (Name) obj;
        if (firstName == null) {
            if (other.firstName != null)
                return false;
        } else if (!firstName.equals(other.firstName))
            return false;
        if (lastName == null) {
            if (other.lastName != null)
                return false;
        } else if (!lastName.equals(other.lastName))
            return false;
        if (middleName == null) {
            if (other.middleName != null)
                return false;
        } else if (!middleName.equals(other.middleName))
            return false;
        return true;
    }
    @Override
    public String toString() {
        return "Name [firstName=" + firstName + ", middleName=" + middleName
                + ", lastName=" + lastName + "]";
    }

}

现在我有一份像这样的学生名单

List<Student> studentList = getStudents(); //some method to create the list

现在，让我们试一下分组示例。这是一个多级分组，首先我使用Gender对其进行分组，然后对名字进行分组（不重要）。这是代码：

Map<Student.Gender, Map<String, List<Student>>> studentsByGenderName = 
                                     studentList.stream()
                                                .collect(Collectors.groupingBy(Student::getGender,
                                                        Collectors.groupingBy(std ->  std.getName().getFirstName().substring(0, 4))));

这在第二个收集器中给出了一个错误，声明＆＃34;方法getName（）未定义为Object＆＃34;类型。现在，我能够通过提供＆＃39; std＆＃39;像这样：

 Map<Student.Gender, Map<String, List<Student>>> studentsByGenderName = 
                                 studentList.stream()
                                            .collect(Collectors.groupingBy(Student::getGender,
                                                    Collectors.groupingBy((Student std) ->  std.getName().getFirstName().substring(0, 4))));

我的问题是为什么java不能推断第二个收集器中使用的lambda表达式中的参数类型，而它能够为第一个收集器做到这一点？