问题描述
- 学到java集合框架中对那个复写equals的疑问,求解答
-
import java.util.*;
class Student implements Comparable
{
private String name;
private int age;
Student(String name,int age)
{
this.name = name;
this.age = age;
}
public int compareTo(Student s)
{
int num = new Integer(this.age).compareTo(new Integer (s.age));
if(num==0)
return this.name.compareTo(s.name);
return num;
}public int hashCode() { return name.hashCode()+age*34; } public boolean equals(Object obj) { if(!(obj instanceof Student)) throw new ClassCastException("类型不匹配"); Student s = (Student)obj; return this.name.equals(s.name) && this.age==s.age;//这里可不可以写成 return this.name == s.name &&this.age==s.age; } public String getName() { return name; } public int getAge() { return age; } public String toString() { return name+":"+age; }
}
class MapTest
{
public static void main(String[] args)
{
HashMap hm = new HashMap();hm.put(new Student("lisi1",21),"beijing"); hm.put(new Student("lisi2",22),"shanghai"); hm.put(new Student("lisi3",23),"nanjign"); hm.put(new Student("lisi4",24),"wuhan"); hm.put(new Student("lisi5",25),"changsha"); //第一种取出方式 keySet System.out.println("第一种方式"); Set<Student> keySet = hm.keySet(); Iterator<Student> it = keySet.iterator(); while(it.hasNext()) { Student stu = it.next(); String addr = hm.get(stu); System.out.println(stu+".."+addr); } System.out.println("第二种方式"); //第二种取出方式 Set<Map.Entry<Student,String>> entrySet = hm.entrySet(); Iterator<Map.Entry<Student,String>> it1 = entrySet.iterator(); while(it1.hasNext()) { Map.Entry<Student,String> me = it1.next(); Student stu = me.getKey(); String addr = me.getValue(); System.out.println(stu+"..."+addr); } }
}
//Student类中复写equals方法 比较名字的时候可不可以把equals换成==呢??
解决方案
String是一个对象,==表示是两个对象是同一个对象,指向同一块内存地址,A.equals(B)表示A的值和B的值相同即可,两者表示的含义不同,所以我认为这里不能换成==
解决方案二:
一个是地址比较,一个是值比较
时间: 2024-12-02 15:32:47