package com.ddy;public class User {    private Integer id;    private String name;    private String address;    private String phone;    public Integer getId() {        return id;    }    public void setId(Integer id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name == null ? null : name.trim();    }    public String getAddress() {        return address;    }    public void setAddress(String address) {        this.address = address == null ? null : address.trim();    }    public String getPhone() {        return phone;    }    public void setPhone(String phone) {        this.phone = phone == null ? null : phone.trim();    }    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + ((id == null) ? 0 : id.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;        User other = (User) obj;        if (id == null) {            if (other.id != null)                return false;        } else if (!id.equals(other.id))            return false;        return true;    }    public User(Integer id) {        super();        this.id = id;    }    }

Person根据id重写了equals和hashCode方法；这样HashSet添加people的时候会将id重复的people对象视为同一个people对象。

package com.ddy;import java.util.HashSet;import java.util.Set;public class Test {    public static void main(String[] args) {        User user1 = new User(1);        User user2 = new User(1);        Set
    
      users = new HashSet<>();        users.add(user2);        users.add(user1);        System.out.println(users);    }}