Java Set集合去重

    Set<8大基本类型> set = new HashSet<8大基本类型>();
    set.add(8大基本类型);

public boolean add(E e) {
	return map.put(e, PRESENT)==null;
	}

public V put(K key, V value) {
        if (key == null)
            return putForNullKey(value);
        int hash = hash(key.hashCode());
        int i = indexFor(hash, table.length);
        for (Entry<K,V> e = table[i]; e != null; e = e.next) {//每添加一个，则循环判断是否与map中的元素相等
            Object k;
            // 先判断hashcode是否一致，然后再判断值是否相等
            if (e.hash == hash && ((k = e.key) == key || key.equals(k))) {
                V oldValue = e.value;
                e.value = value;
                e.recordAccess(this);
                return oldValue;
            }
        }
 
        modCount++;
        addEntry(hash, key, value, i);
        return null;
    }

public class User {
    //id
    protected Integer id;
    //username
    protected String username;

    //构造方法
    public User(int id,String username){
        this.id = id;
        this.username = username;
    }

    /**
     * 如果对象是USER，先比较hashcode，一致的场合在比价每个属性的值
     */
    @Override
    public boolean equals(Object obj) {
        if(obj == null)
            return false;
        if(this == obj)
            return true;
        if(obj instanceof User){
            User user = (User) obj;
            //if(user.id == this.id) return true; //只比较id
            //比较id和username 一致时才返回true，之后再去比较hashCode
            if(user.id == this.id && user.username.equals(this.username)){
                return true;
            }
        }
        return false;
    }

    /**
     *
     * 重写hashCode方法，返回的hashCode不一样 才认为是不一样的对象；
     */
    @Override
    public int hashCode() {
        //return id.hashCode();  只比较id，id不一样就添加进集合；
        return id.hashCode() * username.hashCode();
    }
}

import java.util.HashSet;
import java.util.Set;

public class test {
    public static void main(String[] args){
        User user1 = new User(1,"xiaoqiang");
        User user2 = new User(2,"xiaoqiang");
        User user3 = new User(1,"xiaoqiang");
        User user4 = new User(1,"xiaoqiang");

        Set<User> set = new HashSet<User>();
        set.add(user1);
        set.add(user2);
        set.add(user3);
        set.add(user4);
        for(User u : set){
            System.out.println("id:" + u.id +" username:"+ u.username);
        }
    }
}

id:2 username:xiaoqiang
id:1 username:xiaoqiang