How String actually works?

You already know what a String is and how to work with it. This chapter will cover the theoretical aspects of what lies inside a String.

Let's explore the underlying representation of String values in Java. Initially, String was implemented as an array of char values, which was straightforward and intuitive. However, it later transitioned to an array of byte values. Let's understand the rationale behind this change.

A char variable in Java occupies 4 bytes of memory, while a byte variable only requires 1 byte. By utilizing byte values, we can significantly reduce the memory footprint, utilizing only one-fourth of the space.

But how does a String accommodate various characters, including non-numeric ones? The mechanism is akin to that of a char variable. We leverage the ASCII table, where numerical data is mapped to specific characters, enabling the representation of a wide range of characters in a String.

Let's take a look at an illustration representing the String value "Hello":

The cells contain type byte elements, which we take from the ASCII table. We can even view in the code the exact byte array that is stored in the value of a String variable. This can be done using the getBytes() method.

Let's take a look at an example code:

We can see that the byte values are identical to those shown in the diagram above. Additionally, if you're interested, you can refer to the ASCII table and compare the code of each element with its corresponding value.

We can manipulate this byte[] array that we obtain from a String object.