# String Pool

String pool is a memory structure at runtime that holds string objects and enables avoiding extra memory allocations when creating a new string object\. The string pool exists because strings are immutable and have an interning mechanism\.

In C\# and Java, string interning helps store a single `String` instance in memory for all identical strings\. If an application handles many duplicated strings, there's no need to create a new `String` object when a value already exists\. Instead, an existed instance can be reused from the intern table\.

String literals are interned automatically; however, developers can manually intern strings using the `intern` method\.

The process of creating a string using the `"hello"` literal looks like this:

1. The string pool searches for an object with the same value\. If it's found, its reference is returned\.
1. If the string isn't found, a new string object is created, placed in the pool, and then its reference is returned\.

## String comparison specifics in Java

Since the pool ensures that identical strings have identical references, they can be compared using the `==` operator:

```cpp
String a = "hello";
String b = "hello";
System.out.println(a == b); // true
```

Creating a string with the class constructor produces a new object outside the string pool unless the `intern()` method is explicitly invoked\. In this case, the string comparison results will always return `false`\.

```cpp
String a = new String("hello");
String b = "hello";
System.out.println(a == b); // false
```

Therefore, it pays to be extra cautious when comparing strings using the `==` operator in Java\. The string from an external library or other program location may have been created via a constructor and not be interned\.

If there's no guarantee whether the string is in the pool, it'd be better to use string comparison with the `String.equals()` method\. It compares the internal string contents and doesn't depend on the string pool or the interning mechanism\.

```cpp
String a = new String("hello");
String b = "hello";
System.out.println(a.equals(b)); // true
```