Immutable String and Interned Strings

A String object is immutable; its contents cannot be changed. Does the following code change the contents of the string?
String s = "Java"; s = "HTML";
The answer is no. The first statement creates a String object with the content “Java” and assigns its reference to s. The second statement creates a new String object with the con- tent “HTML” and assigns its reference to s. The first String object still exists after the assignment, but it can no longer be accessed, because variable s now points to the new object, as shown in Figure

Since strings are immutable and are ubiquitous in programming, the JVM uses a unique instance for string literals with the same character sequence in order to improve efficiency and save memory. Such an instance is called interned. For example, the following statements:

class immutable
{
public static void main(String[] arg)
{
String str1 = "Welcome to Smartprogrammeron.blogspot.in";
String str2 = new String("Welcome to Smartprogrammeron.blogspot.in");
String str3 = "Welcome to Smartprogrammeron.blogspot.in";
System.out.println("strt1 == str2 is " + (str1 == str2));
System.out.println("str1 == str3 is " + (str1 == str3));
}
}

In the preceding statements, strt1 and str3 refer to the same interned string “Welcome to Smartprogrammeron.blogspot.in”, therefore strt1 == str3 is true. However, strt1 == str2 is false, because strt1 and str2 are two different string objects, even though they have the same contents.