30 Practical Java Code Optimization Tips to Boost Performance

30 Practical Java Code Optimization Techniques

This guide presents thirty proven tips for improving Java applications, covering string handling with String.format, buffered I/O streams, reducing nested loops using maps, proper resource closing, using connection pools, caching reflection results, leveraging CompletableFuture for parallel calls, lazy loading patterns, pre‑sizing collections, avoiding large transactions, replacing long if…else chains with strategy factories, preventing dead loops, handling BigDecimal correctly, writing clear constant names, placing constants first in equals checks, using SimpleDateFormat safely, creating custom thread pools instead of Executors, and avoiding mutable lists from Arrays.asList. Each tip includes concise code snippets.

String url = String.format("http://example.com?user=%s&id=%s", user, id);

BufferedInputStream bis = new BufferedInputStream(new FileInputStream(src));
BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(dest));

Never modify a collection while iterating with foreach; use an iterator or indexed loop.