javaÃæÊÔÖÐһЩString³£¼ûÎÊÌâ
String s = new String("abc");
String s1 = "abc";
String s2 = new String("abc");
System.out.println(s == s1);
System.out.println(s == s2);
System.out.println(s1 == s2);
String s = new String("abc");
String s1 = "abc";
String s2 = new String("abc");
System.out.println(s == s1);
System.out.println(s == s2);
System.out.println(s1 == s2);
ÇëÎÊÒÔÉϳÌÐòÖ´Ðнá¹ûÊÇʲô£¿
µÚÒ»¾äÖ´ÐкóÄÚ´æÖÐÓÐÁ½¸ö¶ÔÏ󣬶ø²»ÊÇÒ»¸ö¡£Ò»¸öÓÉnew String("abc")ÖеÄ"abc"ÔÚString PoolÀïÉú³ÉÒ»¸öֵΪ"abc"µÄ¶ÔÏó£»µÚ¶þ¸öÓÉnewÔÚ¶ÑÀï²úÉúÒ»¸öֵΪ"abc"µÄ¶ÔÏ󣬸öÔÏóÍêÈ«ÊÇString PoolÀïµÄ"abc"µÄÒ»¸ö¿½±´¡£±äÁ¿s×îºóÖ¸Ïò¶ÑÖвúÉúµÄ"abc"¶ÔÏó£»
µÚ¶þ¾äÖ´ÐÐʱ£¬s1ÏÈÈ¥String PoolÕÒÊÇ·ñÓÐֵΪ"abc"µÄ¶ÔÏ󣬺ÜÏÔÈ»ÔÚÉÏÒ»²½ÖÐjavaÒѾÔÚString PoolÀïÉú³ÉÒ»¸ö"abc"¶ÔÏóÁË£¬ËùÒÔs1Ö±½ÓÖ¸ÏòString PoolÖеÄÕâ¸ö"abc"£»
µÚÈý¾äÖÐÓÖÓÐÒ»¸önew£¬ÔÚjavaÖз²Óöµ½newʱ£¬¶¼»áÔÚ¶ÑÀï²úÉúÒ»¸öеĶÔÏó¡£Òò´Ë£¬¸Ã¾äÖ´Ðкó¶ÑÀïÓÖ¶àÁËÒ»¸ö"abc"¶ÔÏó£¬ÕâÓëÖ´ÐеÚÒ»¾äºóÉú³ÉµÄ"abc"ÊDz»Í¬µÄÁ½¸ö¶ÔÏó£¬s2×îºóÖ¸ÏòÕâ¸öÐÂÉú³ÉµÄ¶ÔÏó¡£
Òò´Ë£¬Ö´ÐкóÃæµÄ´òÓ¡Óï¾äµÄ½á¹ûÊÇÈý¸öfalse
ÎÊÌâ2:
Java´úÂë
System.out.println(s == s.intern());
System.out.println(s1 == s1.intern());
System.out.println(s1.intern() == s2.intern());
System.out.println(s == s.intern());
System.out.println(s1 == s1.intern());
System.out.println(s1.intern() == s2.intern());
ÇëÎÊÒÔÉϳÌÐòÖ´Ðнá¹ûÊÇʲô£¿
ÉèsΪStringÀàÐ͵ıäÁ¿£¬µ±Ö´ÐÐs.intern()ʱ£¬javaÏÈÔÚString PoolÀïÕÒÓë×Ö·û´®±äÁ¿sÏàµÈ(ÓÃequals()·½·¨)µÄ×Ö·û´®£¬ÈôÓÐÔò½«ÆäÒýÓ÷µ»Ø£»ÈôûÓÐÔòÔÚString PoolÀï´´½¨Ò»¸öÓësµÄÖµÏàµÈµÄ×Ö·û´®¶ÔÏ󣬲¢½«ÆäÒýÓ÷µ»Ø¡£´ÓÖÐÎÒÃÇ¿ÉÒÔ×ܽá³öintern()·½·¨ÎÞÂÛÈçºÎ¶¼½«·µ»ØString PoolÀïµÄ×Ö·û´®¶ÔÏóµÄÒýÓá£
Òò´Ë£¬ÒÔÉϳÌÐòÖ´ÐеĽá¹ûÊÇfalse£¬true£¬true¡£
PS:ÉèsºÍtΪÁ½¸ö×Ö·û´®±äÁ¿£¬ÈôÓÐs.equals(t)£¬±ØÓÐs.intern() == t.intern()£»
PS:"=="ÓÀÔ¶±È½ÏµÄÊÇÁ½±ß¶ÔÏóµÄµØÖ·ÊÇ·
Ïà¹ØÎĵµ£º
1£® ¹ØÓÚ¶¯Ì¬¼ÓÔØ»úÖÆ??
ѧϰJava±ÈC++¸üÈÝÒ×Àí½âOOPµÄ˼Ï룬±Ï¾¹C++»¹»ìºÏÁ˲»ÉÙÃæÏò¹ý³ÌµÄ³É·Ö¡£ºÜ¶àÈ˶¼Äܱ³³öÀ´JavaÓïÑÔµÄÌØµã£¬ËùνµÄ¶¯Ì¬¼ÓÔØ»úÖÆµÈµÈ¡£µ±È»¸ÅÄîÍùÍùÊÇÏȼÇס¶øºóÏû»¯µÄ£¬¿ÉÓжàÉÙÈËÕæÕýÈ¥Ìå»á¹ý¶¯Ì¬¼ÓÔØµÄ»úÖÆ£¬ÊÔͼȥѰÕÒ¹ýÆäÖеÄϸ½ÚÄØ? Ìṩ´ó¼ÒÒ»¸ö·½·¨£º
ÔÚÃüÁîÐд°¿ÚÔËÐÐJava³ÌÐòµÄÊ ......
ÏÂÊöÊ®Ëĸö¼¼ÇÉ£¬ÊÇÐí¶àÈËÔÚ´óÁ¿µÄÊý¾Ý¿â·ÖÎöÓëÉè¼ÆÊµ¼ùÖУ¬Öð²½×ܽá³öÀ´µÄ¡£¶ÔÓÚÕâЩ¾ÑéµÄÔËÓ㬶ÁÕß²»ÄÜÉú°ïÓ²Ì×£¬ËÀ¼ÇÓ²±³£¬¶øÒªÏû»¯Àí½â£¬ÊµÊÂÇóÊÇ£¬Áé»îÕÆÎÕ¡£²¢Öð²½×öµ½£ºÔÚÓ¦ÓÃÖз¢Õ¹£¬ÔÚ·¢Õ¹ÖÐÓ¦Óá£
1. Ôʼµ¥¾ÝÓëʵÌåÖ®¼äµÄ¹ØÏµ
¡¡¡¡
¿ÉÒÔÊÇÒ»¶ÔÒ»¡¢Ò»¶Ô¶à¡¢¶à ......
http://blog.csdn.net/ycyangcai/archive/2009/06/21/4285997.aspx
1.ÉùÃ÷Ò»¸ömap: Map map = new HashMap();
2.ÏòmapÖзÅÖµ,×¢Ò⣺mapÊÇkey-valueµÄÐÎʽ´æ·ÅµÄ.Èç:
map.put("sa","dd");
3.´ÓmapÖÐȡֵ:String str = map.get("sa").toString();½á¹ûÊÇ:str = "dd";
4.±éÀúÒ»¸ömap£¬´Ó ......
Map map = new HashMap();
Iterator it = map.entrySet().iterator();
while (it.hasNext()) {
Map.Entry entry = (Map.Entry) it.next();
Object key = entry.getKey();
Object value = entry.getValue();
}
......
Caused by: java.sql.SQLException: ORA-00918: column ambiguously defined
Caused by: com.ibatis.common.jdbc.exception.NestedSQLException:
--- The error occurred in com/ibatis/jpetstore/persistence/sqlmapdao/sql/Item.xml.
--- The error occurred while applying a parameter map.&nbs ......