java - hashcode 和 equals 方法未被覆盖 - put 和 get 将如何工作？

Question

我有一个类(class) Student 和 Marks。我正在使用 Student Object 作为 HashMap 的 Key 和 Marks 作为 Value。如果我不覆盖 hashMap 和 equals，它仍然可以正常工作。

我。如果不覆盖 equals() 和 hashcode()，有人能解释一下它在内部是如何工作的吗二.如果我只覆盖 hashcode()

会怎么样

iii.如果我只覆盖 equals()

class Student {

    String name;
    public String getLastName() {
        return lastName;
    }
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    String lastName;

    Student(String name, String lastName){
        this.name = name;
        this.lastName = lastName;
    }
    public String toString(){
        return(" Name : " + this.getName() + " Last Name : " + this.getLastName());
    }
}
class Marks {
    Student s;
    String marks;
    public Student getS() {
        return s;
    }
    public void setS(Student s) {
        this.s = s;
    }
    public String getMarks() {
        return marks;
    }
    public void setMarks(String marks) {
        this.marks = marks;
    }
    Marks (Student s, String marks){
        this.marks = marks;
        this.s = s;
    }
    public String toString(){
        return(" Marks : " + this.getMarks());
    }
}



public class Main {
    public static void main(String[] args) {
        Student s1 = new Student("Vishnu","Verma");
        Student s2 = new Student("Amit","Sharma");

        Marks m1 = new Marks(s1,"65%");
        Marks m2 = new Marks(s2,"67%");

        Map <Student,Marks>map = new HashMap<Student,Marks>();
        map.put(s1, m1);
        map.put(s2, m2);

        System.out.println(map);
    }
}

Answer 1

如果对象的引用相等，它将认为对象相等。即它们指向同一个对象。