Why does appending "" to a String save memory?

A closer look at string immutability and interning

In Java, a string's immutability ensures it can't be changed once it's created. This spawns a performance issue - repeated string operations may produce many immutable objects, hogging the memory.

Appending "" can trigger string interning – the JVM checks if an identical string already exists; if it does, that instance is reused. This is crucial for memory optimization, because potentially numerous string instances can be reduced to a reference to a single instance in the pool.

Substrings and sneaky memory leaks

But even interning has its limits. Memory leaks can spring up, specifically when using substring operations on large strings. Until Java 7 update 6, substrings referred to the same internal char array as the original string, potentially consuming memory in an inefficient manner.

Java 8 changed the game by ensuring substring creates a new char array, but if the original strings are kept, memory issues can still arise. A common workaround is to use the new String constructor to create a new string, and consequently, get rid of the reference to the original large string’s char array.

Example:

String largeString = "Very large string";
String smallSubstring = new String(largeString.substring(0, 10)); // Who needs a big chunk when a small bite will do?
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Here, smallSubstring doesn't reference the largeString's char array, so the garbage collector can free up the memory originally held by the string.

Smarter way to process strings

String processing can be done more efficiently by breaking the data into smaller chunks. Ensure that large original strings are promptly discarded once they're no longer needed. Remember to create distinct string instances when working on parts of large strings to save memory.

Picture these scenarios:

• Substring without "": Holds on to the original string’s char array.
• Append "" to substring: May lead to a new, interned string.
• Using new String constructor: Purposefully gets rid of the large string reference.

Understanding these implications can reduce memory usage and avoid leaks by mindfully manipulating strings.

Pulling the breaks on memory hogging strings

Reducing unnecessary memory usage requires some elbow grease:

• Input processing: If you have a big, juicy input, chop it into manageable, bite-sized pieces.
• Clear references: Once you're done with bigger context strings, trash 'em. Make it easier for the garbage collector.
• String immutability: Understand when new strings come into being and how your operations affect the underlying char arrays.

By following these tactics, you can minimize your application’s memory footprint, making it faster and more efficient.