How do objects get into the String Pool?

Objects of the String class are added to the String Pool mainly in two ways:

1. Using a string literal: When you create a string using a literal (for example, "hello"), the Java Virtual Machine (JVM) first checks the String Pool. If a string with the same content already exists, a reference to it is returned. Otherwise, a new string is created in the String Pool, and a reference to the new object is returned.

   // String literal
   String s1 = "hello"; // The object "hello" is created or found in the String Pool
   String s2 = "hello"; // s2 gets a reference to the same "hello" object from the String Pool
   

2. Calling the intern() method: The intern() method is called on a String object and returns the canonical representation of the string. If a string with the same content already exists in the String Pool, a reference to it is returned. If not, the string is added to the String Pool, and a reference to the added object is returned.

   // Creating a string via new
   String s3 = new String("world"); // A new "world" object is created in the heap, not in the String Pool
   
   // Using the intern() method
   String s4 = s3.intern(); // "world" is added to the String Pool (if not already there), and s4 gets a reference to it
   String s5 = "world"; // s5 gets a reference to the "world" object from the String Pool (the same as s4)
   

Thus, the String Pool serves to cache frequently used string literals, optimizing memory usage, since different references can point to the same string object in the pool. Strings created via new String(...) are initially not placed in the pool until the intern() method is explicitly called.