修改hashset中对象的属性值，且属性值是计算哈希值的字段，这时会引起内存泄漏
即：当一个对象被存储进HashSet集合中以后，就不能修改该对象的参与计算哈希值的属性值了 ，否则对象修改后的哈希值与最初存储进HashSet集合中时的哈希值就不同了，在这种情况下，即使在contains方法使用该对象的当前引用作为参数去HashSet集合中检索对象，也将返回找不到对象的结果，这也会导致无法从HashSet集合中删除当前对象，造成内存泄露。
举例说明：
public class HashSetTest { public static void main(String[] args) { Set<Person> set = new HashSet<Person>(); Person p1 = new Person("唐僧", "pwd1", 25); Person p2 = new Person("孙悟空", "pwd2", 26); Person p3 = new Person("猪八戒", "pwd3", 27); set.add(p1); set.add(p2); set.add(p3); System.out.PRintln("总共有:" + set.size() + " 个元素!"); //结果：总共有:3 个元素! p3.setAge(2); //修改p3的年龄,此时p3元素对应的hashcode值发生改变 set.remove(p3); //此时remove不掉，造成内存泄漏 set.add(p3); //重新添加，居然添加成功 System.out.println("总共有:" + set.size() + " 个元素!"); //结果：总共有:4 个元素! for (Person person : set) { System.out.println(person); } }}public class Person { private String username; private String passWord; private int age; public Person(String username, String password, int age) { this.username = username; this.password = password; this.age = age; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + age; result = prime * result + ((password == null) ? 0 : password.hashCode()); result = prime * result + ((username == null) ? 0 : username.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 (password == null) { if (other.password != null) return false; } else if (!password.equals(other.password)) return false; if (username == null) { if (other.username != null) return false; } else if (!username.equals(other.username)) return false; return true; } @Override public String toString() { return this.username + "-->" + this.password + "-->" + this.age; }}新闻热点
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