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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);
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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());
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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 ......

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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(); 

......

JPetStore 5.0(iBATIS for java)ÖÐItem.xmlµÄbug

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 ......
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