import java.util.HashMap;

public class Test {

    public Test() {
        // TODO Auto-generated constructor stub
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Person person1 = new Person();
        Person person2 = new Person();

        person1.name 
 
= "furong";
        person1.age = 12;

        person2.name = "furong";
        person2.age = 12;

        HashMap<Person, String> map = new HashMap<Person, String>();
        map.put(person1, "person1");

        System.out.println(map.get(person2));

        System.out.println(person1);
    }

}
 

執行結果

null
Person.Person@15db9742

複寫hashCode和toString

package Person;

public class Person {

    String name;
    int age;

    public Person() {
        // TODO Auto-generated constructor stub
    }

    public int hashCode() {
        int result = 17;

        result = 31 * result * age;
        result 
 
= 31 * result * name.hashCode();

        return result;
    }

    public String toString() {
        return "name: " + name + ", age: " + age;
    }

}

執行結果

person1
name: furong, age: 12