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：3three4four1one2two5five可见唯一！
