When should we use intern method of String on String literals

user_94813 0
Viewed 116693

According to String#intern(), intern method is supposed to return the String from the String pool if the String is found in String pool, otherwise a new string object will be added in String pool and the reference of this String is returned.

So i tried this: 

String s1 = "Rakesh";
String s2 = "Rakesh";
String s3 = "Rakesh".intern();

if ( s1 == s2 ){
    System.out.println("s1 and s2 are same");  // 1.
}

if ( s1 == s3 ){
    System.out.println("s1 and s3 are same" );  // 2.
}

I was expecting that s1 and s3 are same will be printed as s3 is interned, and s1 and s2 are same will not be printed. But the result is: both lines are printed. So that means, by default String constants are interned. But if it is so, then why do we need the intern method? In other words when should we use this method?

string-interning java string
14 Answers
String s1 = "Anish";
        String s2 = "Anish";

        String s3 = new String("Anish");

        /*
         * When the intern method is invoked, if the pool already contains a
         * string equal to this String object as determined by the
         * method, then the string from the pool is
         * returned. Otherwise, this String object is added to the
         * pool and a reference to this String object is returned.
         */
        String s4 = new String("Anish").intern();
        if (s1 == s2) {
            System.out.println("s1 and s2 are same");
        }

        if (s1 == s3) {
            System.out.println("s1 and s3 are same");
        }

        if (s1 == s4) {
            System.out.println("s1 and s4 are same");
        }

OUTPUT

s1 and s2 are same
s1 and s4 are same
user_9115760

By using heap object reference if we want to get corresponding string constant pool object reference, then we should go for intern()

String s1 = new String("Rakesh");
String s2 = s1.intern();
String s3 = "Rakesh";

System.out.println(s1 == s2); // false
System.out.println(s2 == s3); // true

Pictorial View enter image description here

Step 1: Object with data 'Rakesh' get created in heap and string constant pool. Also s1 is always pointing to heap object.

Step 2: By using heap object reference s1, we are trying to get corresponding string constant pool object referenc s2, using intern()

Step 3: Intentionally creating a object with data 'Rakesh' in string constant pool, referenced by name s3

As "==" operator meant for reference comparison.

Getting false for s1==s2

Getting true for s2==s3

Hope this help!!

user_36634950
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