~~~ <!-- 配置spring容器需要管理的对象 --> <bean name="user" class="com.nobb.bean.User"></bean> ~~~ **1.重载构造器，没有显示声明无参构造（创建对象失败）** ~~~ public class User { private Integer id; private String name; public User(Integer id){ this.id = id; } ~~~ **2.重载构造器，有无参构造，也有有参构造（创建对象成功）** ~~~ public class User { private Integer id; private String name; public User(){ System.out.println("调用了无参构造"); } public User(Integer id){ this.id = id; } ~~~ 调用了无参构造 User{id=null, name='null'} **3.无参构造声明为private（创建对象成功）** ~~~ public class User { private Integer id; private String name; private User(){ System.out.println("调用了无参构造"); } ~~~ 调用了无参构造 User{id=null, name='null'}