java.lang.OutOfMemoryError: Java heap space

The JVM ran out of heap memory.

Fix 1: Increase heap size

java -Xmx2g -Xms512m MyApp

• -Xmx2g — max heap 2GB
• -Xms512m — initial heap 512MB

Fix 2: Find memory leaks

Common causes:

• Collections that grow without bounds
• Static references holding large objects
• Unclosed resources (streams, connections)

// ❌ Memory leak — list grows forever
static List<byte[]> cache = new ArrayList<>();
void process() {
    cache.add(new byte[1024 * 1024]);
}

Fix 3: Use a profiler

# Generate heap dump on OOM
java -XX:+HeapDumpOnOutOfMemoryError -XX:HeapDumpPath=/tmp MyApp

Then analyze with VisualVM or Eclipse MAT.