java学习笔记（类引用未初始化）

class student
{
  //类会初始化变量
  int age;
  public void say()
  {
    System.out.println("i am a student!");
  }
}

class school
{
  student many;//引用未初始化 直接抛出异常
}

public class main {

  /**
   * @param args
   */
  public static void main(String[] args) {
    // TODO Auto-generated method stub

    school taihu=new school();
    
    taihu.many.say();
  }

}

结果是：

Exception in thread "main" java.lang.NullPointerException

at main.main(main.java:26)

抛出异常！