Should I use Java's String.format() if performance is important?

java

stringbuilder

performance

readability

byNikita Barsukov·Aug 14, 2024

Prefer StringBuilder for high-performance scenarios over String.format():

StringBuilder sb = new StringBuilder();
sb.append("Value1: ").append(val1).append(", Value2: ").append(val2);
String result = sb.toString();

Why? String.format() incurs extra cost because it parses format strings and conducts type conversions; whereas, StringBuilder provides a direct, efficient method for constructing strings, which is critical in performance-sensitive applications.

Advantages of using StringBuilder

StringBuilder is your go-to buddy when your application has to create strings repeatedly or when dealing with a large number of string manipulations, like in the case of logs. This leads to efficient memory use, consequently, preventing creation of multiple string instances and ensuring a smooth garbage collection process.

StringBuilder myLogBuilder = new StringBuilder();
myLogBuilder.append("Here are my logs, not from a tree though!");  // Just a programmer joke!

Moreover, StringBuilder is equally speedy as our old friend the '+' operator, but, triumphantly, it is more memory-efficient.

Drawbacks of using String.format

Here's why String.format() loses the performance race often – it is generally 5-30 times slower than string concatenation using the '+' operator. This is because it engages in extra-curricular activities, such as:

Instantiating a Formatter object
Parsing the input format strings
Handling implicit type conversions

Balance: Performance vs Readability

As in life, balance is crucial in programming too. While StringBuilder may seem like an obvious choice for heavy-duty performance, the elegance and readability provided by String.format() can be a trade-off worth considering. After all, clear and maintainable code is also a sign of a great programmer.

Benchmarking for optimal results

Promise to make an informed decision? Do performance testing. Period. For reliable benchmarking, you might consider using JMH (Java Microbenchmark Harness). Also, test across different JVM versions to see if your application aligns well with the latest optimizations.