What is String Pool in java?

Answer 1

String Pool in java is a pool of Strings stored in Java Heap Memory. String is special class in java and we can create String object using new operator as well as providing values in double quotes. String Pool is possible only because String is immutable in Java and it’s implementation of String interning concept. String pool is also example of Flyweight design pattern. String pool helps in saving a lot of space for Java Runtime although it takes more time to create the String. When we use double quotes to create a String, it first looks for String with same value in the String pool, if found it just returns the reference else it creates a new String in the pool and then returns the reference.
However using new operator, we force String class to create a new String object in heap space. We can use intern() method to put it into the pool or refer to other String object from string pool having same value.

Here is the java program for the String Pool image:

public class StringPool {

    /**
     * Java String Pool example
     * @param args
     */
    public static void main(String[] args) {
        String s1 = "Cat";
        String s2 = "Cat";
        String s3 = new String("Cat");

        System.out.println("s1 == s2 :"+(s1==s2));
        System.out.println("s1 == s3 :"+(s1==s3));
    }

}

Output of the above program is:

s1 == s2 :true
s1 == s3 :false