关于重写equals()与hashCode()

在HashMap与HashSet中，是不允许元素重复的。

在判定时比较元素的hashCode()是否相等，equals()是否返回true，那么问题来了

这是一个Person类

public class Person {
   private String id;
   private String name;
   private Integer age;
   public String getId() {
       return id;
   }
   public void setId(String id) {
       this.id = id;
   }
   public String getName() {
       return name;
   }
   public void setName(String name) {
       this.name = name;
   }
   public Integer getAge() {
       return age;
   }
   public void setAge(Integer age) {
       this.age = age;
   }
   @Override
   public String toString() {
       return "Person [id=" + id + ", name=" + name + ", age=" + age + "]";
   }
   @Override
   public int hashCode() {
       final int prime = 31;
       int result = 1;
       result = prime * result + ((age == null) ? 0 : age.hashCode());
       result = prime * result + ((id == null) ? 0 : id.hashCode());
       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 == null) {
           if (other.age != null)
               return false;
       } else if (!age.equals(other.age))
           return false;
       if (id == null) {
           if (other.id != null)
               return false;
       } else if (!id.equals(other.id))
           return false;
       if (name == null) {
           if (other.name != null)
               return false;
       } else if (!name.equals(other.name))
           return false;
       return true;
   }
   /*@Override
   public int hashCode() {
       System.out.println("id = " + id + ";id.hashCode = " + id.hashCode());
       return id.hashCode();
   }
   @Override
   public boolean equals(Object obj) {
       System.out.println("equals");
       Person p = (Person)obj;
       if(this.id == p.id) {
           return true;
       }else{
           return false;
       }
   }*/
}

这是一个Test类

public class TestHashCode {
   public static void main(String[] args) {
       Set<Person> set = new HashSet<Person>();
       Person p1 = new Person();
       p1.setId("11");
       p1.setName("张三");
       p1.setAge(20);
       Person p2 = new Person();
       p2.setId("11");
       p2.setName("李四");
       p2.setAge(30);
       set.add(p1);
       set.add(p2);
       System.out.println(p1.hashCode() == p2.hashCode());
       System.out.println(p1.equals(p2));
       for (Person person : set) {
           System.out.println(person.toString());
       }
   }
}