HashSet<String> hst1 = new HashSet<String>();
hst1.add("1");
String ss = "123";
System.out.println(ss.charAt(0));
if (hst1.contains(ss.charAt(0)))
System.out.println("yes");
else
System.out.println("no");
输出是no
这是因为contains内部是比较hash值的，字符串“1”的hash值和字符'1'的哈希值不一样