~~~ <!-- 配置spring容器需要管理的對象 --> <bean name="user" class="com.nobb.bean.User"></bean> ~~~ **1.重載構造器，沒有顯示聲明無參構造（創建對象失敗）** ~~~ public class User { private Integer id; private String name; public User(Integer id){ this.id = id; } ~~~ **2.重載構造器，有無參構造，也有有參構造（創建對象成功）** ~~~ public class User { private Integer id; private String name; public User(){ System.out.println("調用了無參構造"); } public User(Integer id){ this.id = id; } ~~~ 調用了無參構造 User{id=null, name='null'} **3.無參構造聲明為private（創建對象成功）** ~~~ public class User { private Integer id; private String name; private User(){ System.out.println("調用了無參構造"); } ~~~ 調用了無參構造 User{id=null, name='null'}