JVM Performance Tuning

JVM Flags

Heap Size

java -Xms512m -Xmx2g MyApp

• -Xms: Initial heap size
• -Xmx: Maximum heap size

GC Selection

java -XX:+UseG1GC MyApp

Common GC options:

• -XX:+UseSerialGC - Single-threaded GC
• -XX:+UseParallelGC - Parallel GC (default)
• -XX:+UseG1GC - G1 Garbage Collector
• -XX:+UseZGC - Z Garbage Collector (low latency)

Profiling Tools

1. JConsole

Built-in monitoring tool for memory, threads, and CPU.

2. VisualVM

Advanced profiling and monitoring.

3. JProfiler / YourKit

Commercial profilers with advanced features.

Performance Best Practices

1. Avoid Premature Optimization

"Premature optimization is the root of all evil" - Donald Knuth

Measure first, then optimize.

2. Use StringBuilder for String Concatenation

// Bad
String result = "";
for (int i = 0; i < 1000; i++) {
    result += i; // Creates new String each time!
}

// Good
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 1000; i++) {
    sb.append(i);
}
String result = sb.toString();

3. Use Appropriate Collections

• ArrayList for random access
• LinkedList for frequent insertions/deletions
• HashMap for key-value lookups

4. Lazy Initialization

Initialize expensive objects only when needed.

private ExpensiveObject obj;

public ExpensiveObject getObject() {
    if (obj == null) {
        obj = new ExpensiveObject();
    }
    return obj;
}

Monitoring GC

java -XX:+PrintGCDetails -XX:+PrintGCTimeStamps MyApp

Quiz