关于toString()的问题

User类的代码：

public class User {

private String name;

private String sex;

private int age;

private String address;

public User(String name,String sex,int age,String address){

this.name=name;

this.sex=sex;

this.age=age;

this.address=address;

}

public String toString(){

return name+"\t"+sex+"\t"+age+"\t"+address;

}

main方法：

public static void main(String[] args) {

// TODO 自动生成的方法存根

List<User> users=new ArrayList<User>();

User user1=new User("小王","男",18,"南京市");

User user2=new User("小李","男",21,"盐城市");

User user3=new User("小红","女",24,"上海市");

users.add(user1);

users.add(user2);

users.add(user3);

for(int i=0;i<users.size();i++){

System.out.println(users.get(i));

}

}

userList.get(i)获得的是User对象，为什么最后把User类的属性内容都打印了

这里是怎么调用toString()方法的