javalangOutOfMemoryError

java.lang.OutOfMemoryError is a runtime error raised by the Java Virtual Machine when it cannot allocate memory for an object or for native process operations. It signals that the JVM has exhausted memory resources and cannot continue normal execution.

The error manifests in several forms, depending on the exhausted memory region. Java heap space occurs when there is no room for new objects on the heap. GC overhead limit exceeded indicates excessive time spent performing garbage collection without freeing enough memory. Metaspace (or PermGen in older JVMs) refers to memory available for class metadata. Other variants include unable to create new native thread, which happens when the operating system or JVM limits prevent creating more threads, and direct buffer memory, which relates to off-heap memory used by direct byte buffers.

Causes of an OutOfMemoryError include memory leaks, retaining large collections or objects longer than necessary, processing very large data sets, and insufficient or misconfigured heap or metaspace sizes. Excessive native allocations or a high number of concurrent threads can also trigger native memory exhaustion. Diagnosis typically involves monitoring memory usage and GC behavior, reviewing GC logs, and analyzing heap dumps with tools such as VisualVM or Eclipse MAT.

Mitigation strategies focus on reducing memory pressure and adjusting JVM limits. Common steps are increasing heap size with -Xmx, tuning or changing the garbage collector, increasing MaxMetaspaceSize, and addressing memory leaks or cache growth in the application. Reducing per-object memory usage or the total number of simultaneously live objects can help, as can decreasing thread count or per-thread stack size to avoid native memory exhaustion.

Catching OutOfMemoryError is possible but generally discouraged, since it indicates a condition that is difficult to recover from reliably. Applications are typically expected to fail fast and log diagnostic information for later analysis.