hascode和equals方法没有被覆盖 - put和get将如何工作？ [英] hascode and equals methods not overridden - How the put and get will work?

问题描述

我有一个班学生和商标。
我使用 Student Object 作为 HashMap 并标记为值。
如果我不覆盖 hashMap 和equals，它仍然可以正常工作。

i。如果不覆盖 equals（）和 hashcode（） $ b，是否有人可以解释它在内部如何工作？ $ b ii。如果我只覆盖 hashcode（）

iii.what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; 
} 
字符串姓氏; 
 
 Student（String name，String lastName）{
 this.name = name; 
 this.lastName = lastName; 
} 
 public String toString（）{
 return（Name：+ this.getName（）+Last Name：+ this.getLastName（））; 
} 
} 
类标记{
学生s; 
字符串标记; 
 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; 
} 
标记（学生，字符串标记）{
 this.marks =标记; 
 this.s = s; 
} 
 public String toString（）{
 return（Marks：+ this.getMarks（））; 
 
 
 
 
 
 public class Main {
 public static void main（String [] args）{
 Student s1 =新学生（Vishnu，Verma）; 
学生s2 =新生（Amit，Sharma）; 
 
标记m1 =新标记（s1，65％）; 
标记m2 =新标记（s2，67％）; 
 
 Map< Student，Marks> map = new HashMap< Student，Marks>（）; 
 map.put（s1，m1）; 
 map.put（s2，m2）; 
 
 System.out.println（map）; 
} 
} 
  

解决方案

它如果它们的引用相同，它们会认为这些对象相等即它们指向相同的对象。

I have a class Student and Marks. I am using Student Object as Key for HashMap and Marks as Value. If I don't override hashMap and equals, It still works fine.

i. Can someone please explain how does it internally works on it if not overriding both equals() and hashcode() ii. what If I override only hashcode()

iii.what If I override only 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);
    }
}

解决方案

It will consider the objects equal if their references are equal. i.e. they point to the same object.

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