树集的内部工作或HashSet与TreeSet之间的区别

Question

对于可变对象的TreeSet排序：

1. 如果我不重写哈希码等于，那么对于所有字段具有相同值的对象，将被视为set中的两个不同对象（默认对象类哈希码方法计算内存位置的哈希值） 。那么为什么TreeSet会有所不同。请参见下面的示例。

2. 如果我只是将整个Set复制到treeSet中，为什么不进行排序。

。

public class Student {
    private int id;
    private String name;
    private int marks;

    public Student(int id, String name, int marks) {
        super();
        this.id = id;
        this.name = name;
        this.marks = marks;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getMarks() {
        return marks;
    }

    public void setMarks(int marks) {
        this.marks = marks;
    }

    @Override
    public String toString() {
        return "Student [id=" + id + ", name=" + name + ", marks=" + marks + "]";
    }

    public static Comparator<Student> idComparator = new Comparator<Student>() {

        @Override
        public int compare(Student o1, Student o2) {
            return (new Integer(o1.getId())).compareTo(o2.getId());
        }

    };

    public static Comparator<Student> nameComparator = new Comparator<Student>() {

        @Override
        public int compare(Student o1, Student o2) {
            return o1.getName().compareTo(o2.getName());
        }

    };

    /*@Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + id;
        result = prime * result + marks;
        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 (id != other.id)
            return false;
        if (marks != other.marks)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }*/

}

。

public class TestMain {

    public static void main(String[] args) {
        Student s1 = new Student(1, "A", 50);
        Student s2 = new Student(1, "A", 50);
        Student s3 = new Student(2, "B", 51);
        Student s4 = new Student(3, "B", 51);
        Student s5 = new Student(4, "B", 41);
        Student s6 = new Student(5, "B", 61);
        Student s7 = new Student(6, "C", 51);
        Student s8 = new Student(7, "D", 46);
        Student s9 = new Student(8, "B", 55);
        Student s10 = new Student(9, "E", 51);

        List<Student> studentList = new ArrayList<>();
        studentList.add(s1);
        studentList.add(s2);
        studentList.add(s3);
        studentList.add(s4);
        studentList.add(s5);
        studentList.add(s6);
        studentList.add(s7);
        studentList.add(s8);
        studentList.add(s9);
        studentList.add(s10);
        studentList.add(s1);
        studentList.add(s2);
        studentList.add(s3);
        studentList.add(s4);

        System.out.println("List Initial Size: " + studentList.size());

        List<Student> studentListAfterFilter = studentList.stream()
                .filter(p -> p.getMarks() >= 45 && p.getMarks() <= 55).map(p -> p).collect(Collectors.toList());

        System.out.println("After filtering List Size: " + studentListAfterFilter.size());

        Set<Student> studentSetAfterFilter = studentList.stream().filter(p -> p.getMarks() >= 45 && p.getMarks() <= 55)
                .map(p -> p).collect(Collectors.toSet());

        System.out.println("After filtering Set Size: " + studentSetAfterFilter.size());

        for(Student student:studentSetAfterFilter){
            System.out.println("Set Objects: "+student.toString());
        }

        Set<Student> studentTreeSetAfterFilter=new TreeSet<>(Student.nameComparator);
        studentTreeSetAfterFilter.add(s1);
        studentTreeSetAfterFilter.add(s2);
        studentTreeSetAfterFilter.add(s3);
        studentTreeSetAfterFilter.add(s4);
        studentTreeSetAfterFilter.add(s5);
        studentTreeSetAfterFilter.add(s6);
        studentTreeSetAfterFilter.add(s7);
        studentTreeSetAfterFilter.add(s8);
        studentTreeSetAfterFilter.add(s9);
        studentTreeSetAfterFilter.add(s10);
        studentTreeSetAfterFilter.add(s1);
        studentTreeSetAfterFilter.add(s2);
        studentTreeSetAfterFilter.add(s3);
        studentTreeSetAfterFilter.add(s4);

        for(Student student:studentTreeSetAfterFilter){
            System.out.println("TreeSet Objects: "+student.toString());
        }



    }

}