This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
s1.equals(s2);//ok s3=s1.intern(); s4=s2.intern(); if(s3==s4)//ok But if i do:- if(s1==s3)//not ok(not refer to same object); if(s2==s4)//not ok when String method intern is invoke on the String object,it return a reference to a String object that is guaranteed to have the same contant,However,String s1 and String s2 have the same contents,the reference returned by this call to intern is a reference to the String object returned by s1.intern() and s2.intern().But s1==s3 and s2==s4 give that they are not refer to same object,Why?;
s1 = new String("hello") creates a String object with "hello" as the value and enters "hello" into the string literal table. s2 = new String("hello") also creates a String object with "hello" as the value, "hello" is already in the literal table, no entry made. As s1 and s2 are different objects: (s1 == s2)==false s3 = s1.intern() gets the "hello" string object from the literal table and assigns it to s3. s4 = s2.intern() also gets the "hello" string object from the literal table and assigns it to s4. s3 and s4 have reference to the same object, so (s3 == s4) == true. It helps me to remember that s1 (for instance) is a reference to a String object, not the object itself. given that, (s1==s3) doesn't ask 'is s1 equivalent to s3?' but rather 'is the object that s1 refers to the same object as s3 is referring to?' if you were to change s1 = new String("hello") to s1 = "hello", then (s1==s3) would == true, because s1 = "hello" both creates a string object and assigns that same object to s1 and the literal table, which would also be assigned to s3 at: s3 = s1.intern() Does that help?
Note to SCJP candidates: For the exam, it is very important to understand String immutability, and it is important to understand == vs. the equals() method. But just so no one wastes any time, the intern() method itself is NOT on the exam. Thanks, The Focus Police
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