自动装箱、自动拆箱

/**
测试自动装箱、自动拆箱
*/
public class TestAutoBox {
  public static void main(String[] args) {
      Integer a = 234;    //自动装箱。Integer a = Integer.valueOf(234);
      int b = a;          //自动拆箱。编译器会修改成：int b = a.intValue();
      
      System.out.println("a = "+a);
      System.out.println("b = "+b);
      
      Integer c = null;
      if(c!=null) {
          int d = c;      //自动拆箱：调用:c.intValue();
      }
  }
}