集合框架五（hashCode 与Collections）

package us.google.www;

public class Person {
private String name;
private int age;
public Person() {
super();
// TODO Auto-generated constructor stub
}
public Person(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return “Person [name=” + name + “, age=” + age + “]”;
}
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + age;
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;
Person other = (Person) obj;
if (age != other.age)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}

}
package us.google.www;

import java.util.HashSet;

public class HashtableDemo {

public static void main(String[] args) {    HashSet<Person> set = new HashSet<Person>();    Person p1 = new Person("小白",18);    Person p2 = new Person("小黑",19);    System.out.println("p1 hashcode()="+p1.hashCode());    System.out.println("p2 hashcode()="+p2.hashCode());    System.out.println("p1 的散列值="+p1.hashCode()%16);    System.out.println("p2 的散列值="+p2.hashCode()%16);    set.add(p1);    set.add(p2);    set.add(new Person("小白",18));//此对象的hashcode与p1的hashcode一样    System.out.println((new Person("小白",18)).hashCode()==p1.hashCode());    System.out.println(set.size());    //在修改属性后    p1.setAge(19);    System.out.println("p1 hashcode()="+p1.hashCode());    System.out.println("p1 的散列值="+p1.hashCode()%16);    set.remove(p1);    System.out.println(set.size());}

}