空指针产生的条件 null对象调用属性

null对象调用属性 

e.g

public class Student  {
    Integer age;
    String name;
    String address ;
    User user;
}

Student student= new Student(); 

12:student.getUser().getName()

Exception in thread "main" java.lang.NullPointerException
at patterns.builder.Test.main(Test.java:12)