Working Of The String intern() Method
When a string is initialized in Java, it takes up heap memory. We also know the String class is immutable. As a result, anytime we use the new keyword to construct a string, fresh memory is created in a heap for the matching string, regardless of the array's content. Consider the following line of code:
String str = new String("Welcome to Coding Ninjas Studio.");
String str1 = new String("Welcome to Coding Ninjas Studio");
System.out.println(str1 == str); // prints false
In the above snippet, since each string literal is given its memory, the println command returns false. As a result, two new string objects, str and str1, are generated in memory, each with a distinct reference.
In Java, we know that constructing an object is an expensive process. Java developers devised the notion of String Constant Pool (SCP) to save time. The SCP is a section of heap memory. It contains distinct strings. The intern() function must be used to insert strings into the string pool. Before generating an object in the string pool, the JVM checks to see if the string is already existing. If the string exists, the reference to it is returned.
String str = new String("Welcome to Coding Ninjas Studio").intern(); // statement - 1
String str1 = new String("Welcome to Coding Ninjas Studio").intern(); // statement - 2
System.out.println(str1 == str); // prints true
The intern() function is called on the String objects in the above code sample. As a result, memory is allocated in the SCP. Because the contents of str and str1 are identical in the second statement, no new string object is generated. As a result, str1 receives the reference to the object generated in the first statement. As a result, str and str1 both refer to the same memory. As a result, the print assertion is true.
Example-1
public class InternExample
{
public static void main(String args[])
{
String str1=new String("Hello Ninja");
String str2="Hello Ninja";
String str3=s1.intern();
//it will return string from pool, therefore it will be same as str2
System.out.println(str1==str2);
//it will be false because reference variables are pointing to different instance
System.out.println(str2==str3);
//true because reference variables are pointing to same instance
}
}
Output
false
true
Example-2
public class InternExample2 {
public static void main(String[] args) {
String s1 = "Coding Ninjas Studio";
String s2 = s1.intern();
String s3 = new String("Coding Ninjas Studio");
String s4 = s3.intern();
System.out.println(s1==s2); // it will return True
System.out.println(s1==s3); // False
System.out.println(s1==s4); // it will return True
System.out.println(s2==s3); // False
System.out.println(s2==s4); // it will return True
System.out.println(s3==s4); // False
}
}
Output
true
false
true
false
true
false
Frequently Asked Questions
What are mutable and immutable objects in Java?
The value of mutable objects can be altered. Mutable objects include the StringBuilder and StringBuffer. Once created, the value of an immutable object cannot be modified. In Java, a string is an immutable class.
Can we compare strings using the == operator? What is the risk?
Yes, we can use the == operator to compare Strings. When we compare strings with the == operator, we are comparing their object references, determining whether these string variables correspond to the same string object.
Most of the time, developers wish to compare the content of strings, but they compare strings with the == operator rather than the equals() function, which results in an error.
What Is the String Constant Pool?
The String constant pool, sometimes known as the String intern pool, is a specific memory location where the JVM saves String instances.
Conclusion
In this article, we have extensively discussed the String intern() method in Java Programming. We have also discussed its syntax, parameters as well as the return type with the help of examples. We hope this blog has helped you enhance your knowledge regarding string methods in Java Programming.
Recommended Readings:
String contains()
String format().
String isEmpty().
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