判断字符串的引用是否相等

 1 String s1 = "aa";
 2 String s2 = "aabb";
 3 String s3 = "aa"+"bb";
 4         
 5 String s4 = new String("aabb");
 6 String s5 = new String("aabb");
 7         
 8 String s6 = s1 + "bb";
 9 String s7 = s1 + s2;
10 sop(s2==s3);//true
11 sop(s2==s4);//false
12 sop(s4==s5);//false
13 sop(s6==s2);//false
14 sop(s7==s6);//flase