java中的Set集合HashSet集合

1、public class HashSetDemo {

public static void main(String[] args) {

//创建集合

HashSet<Student> hash = new HashSet<Student>();

//创建学生对对象

Student s1 = new Student("one",1);

Student s2 = new Student("two",2);

Student s3 = new Student("two",2);

Student s4 = new Student("three",3);

Student s5 = new Student("four",4);

Student s6 = new Student("four",4);

Student s7 = new Student("five",5);

//添加

hash.add(s1);

hash.add(s2);

hash.add(s3);

hash.add(s4);

hash.add(s5);

hash.add(s6);

hash.add(s7);

//遍历

for(Student s : hash)

{

System.out.println(s.getAge() + s.getName());

//不是说唯一性吗？为什么打印出来发现相同的元素还是有的呢？

//原因是因为低沉用hashcode和equals方法进行比较的

//而对象却没有重写父类Object的hashcode和equals方法！所以当然不同了！

}

}

}

2、所以在学生对象要重写equals和Hashcode方法：

@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;

Student other = (Student) 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;

}

3、打印输出：

3three

4four

1one

2two

5five

可见唯一！