Why Doesn't String's `replace` Method Update My HTML Content?

Java String Replace Conundrum

In an attempt to update values within a String, the provided code employs String's replace method:

String html = "**USERNAME** AND **PASSWORD**";
html.replace("**USERNAME**", "User A");
html.replace("**PASSWORD**", "B");

However, this approach fails to yield the expected results. Why is that so?

String Immutability Bites

The key to understanding this issue lies in String's immutability. Unlike some other objects in Java, Strings cannot be modified in place. Any operation that seems to alter a String, such as replace, actually creates a new String object.

In the given code, the replace calls create new String objects, but the reference html continues to point to the original String. This means the original HTML content is unaffected by the replacement attempts.

The Solution: Embracing Reassignment

To overcome this immutability hurdle, you must reassign the reference html to the new String created by replace. Here's the corrected code:

html = html.replace("**USERNAME**", "User A");
html = html.replace("**PASSWORD**", "B");

By reassigning html after each replace call, you ensure that it points to the updated String containing the desired replacements. This method acknowledges and works around String's immutability to achieve the sought-after replacements.

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