newExc.initCause(e); initCause是什么意思？用来干嘛的

public class ChainTest {

 public static void main(String[] args) {
  ChainTest ct = new ChainTest();
  try{
   ct.test2();
  }catch(Exception e){
   e.printStackTrace();
  }
 }
 public void test1() throws DrunkException{
  throw new DrunkException("喝车别开酒");
 }
 public void test2(){
  try {
   test1();
  } catch (DrunkException e) {
   
   RuntimeException newExc =
    new RuntimeException(e);
   //newExc.initCause(e);
   throw newExc;
  }
 }