What's the Truth Behind Java String Immutability: If Strings Can't Change, Why Does My Code Seem to Modify Them?

What Does "String is Immutable" Really Mean?

When dealing with immutable objects, the fundamental principle is that their contents cannot be altered. However, the code example you provided seems to suggest otherwise, as the value of variable a was successfully changed from "a" to "ty."

To resolve this apparent contradiction, let's delve deeper into the nature of strings in Java.

The String class in Java is indeed immutable, meaning that once a string is created, its value cannot be modified. However, a fundamental distinction exists between a string object and its reference variable.

In your example, when the statement a = "ty" is executed, a new string object is created with the value "ty", and the reference variable a is then reassigned to this new object. This does not violate the immutability of the original string object with the value "a", as it remains unchanged.

It's important to note that while string objects are immutable, their reference variables, like a, can be assigned to different objects. This allows you to effectively modify the contents of a variable, even if the underlying object itself remains unchanged.

To further illustrate this, let's examine what occurs when you perform operations like concatenation on strings. When you use str.concat(" base"), instead of modifying the existing string object, the VM creates a new string object, "knowledge base", and assigns it a new reference, str. This process ensures that the original string object remains unmodified.

Therefore, the concept of string immutability in Java refers to the protection of the object's contents, while still allowing for flexible manipulation of object references. This design approach helps maintain data integrity while facilitating efficient memory management in applications.

The above is the detailed content of What's the Truth Behind Java String Immutability: If Strings Can't Change, Why Does My Code Seem to Modify Them?. For more information, please follow other related articles on the PHP Chinese website!