Traps caused by generics

1 package Stu; 2 3 Import Java. util. arraylist; 4 Import Java. util. list; 5 6 public class testlist {7 public static void main (string [] ARGs) {8 list = new arraylist (); 9 10 list. add ("1"); 11 12 list. add (2); // type inconsistent 13 14 list. add ("3q"); 15 16 for (INT I = 0; I <list. size (); I ++) {17 18 system. out. println (list. get (I); 19 20} 21 22 // The first loop output has no problem, and the second loop reports a transformation exception. In other words, the set itself can store objects of 23 24 // different types of elements, but since jdk1.5, there has been a wildcard, so many of us think that a set variable can only store one type of object element. 25 26 // The generic type is designed to better exclude the tedious check caused by type conversion during compilation. In most applications, the elements of the same type are indeed set. 27 28 // with the new cycle strengthened by the generic model, it will force a single type of transformation operation. 29 30 List <string> listnew = List; 31 32 for (string strnew: listnew) {33 34 system. Out. println (strnew); 35 36} 37} 38}

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