Regarding the pool of strings in Mala Gupta's book

[Mohammad Ali Asgar]

Hello Everyone,

I read in Ch4 of Mala Gupta's book that if a string is created by directly placing a sequence of characters within a pair of " " AND without using the new operator, then the object created is placed in a pool of String objects.

I wonder whether the following piece of code also puts objects (with values Java and Oracle) in that pool since the new operator is not present.

ArrayList<String> exams= new ArrayList<String>();
exams.add("Java"); exams.add("Oracle");

I would appreciate a reply from anyone with decent knowledge of Java.

__ softwarelover

[Roel De Nijs]

Mohammad Ali Asgar wrote:I would appreciate a reply from anyone with decent knowledge of Java.

That's something you can verify yourself if you have a good understanding of the working of the string constant pool.

If they are in the String constant pool, the output will print true, false otherwise.

System.out.println(exams.get(0) == "Java");
System.out.println(exams.get(1) == "Oracle");

[Mohammad Ali Asgar]

Thanks. Yes, i get it now. The == operator will compare references and that can help verify whether strings were created or reused from the pool.

[Roel De Nijs]

Mohammad Ali Asgar wrote:The == operator will compare references and that can help verify whether strings were created or reused from the pool.

[Mohammad Ali Asgar]

ArrayList<String> exams= new ArrayList<String>();
exams.add("Java"); exams.add("Oracle"); exams.add(new String("OCA SE7"));
System.out.println(exams.get(0) == "Java");
System.out.println(exams.get(1) == "Oracle");
System.out.println(exams.get(2) == "OCA SE7"); 

Interesting outputs:

true
true
false

Because of that new operator, two copies of "OCA SE7" exist.

[Roel De Nijs]

Mohammad Ali Asgar wrote:Because of that new operator, two copies of "OCA SE7" exist.

That's well explained in this excellent article.