面试题与答案

The finalize() method is called by the garbage collector before reclaiming the memory occupied by an object. It can be overridden to perform cleanup operations before an object is garbage collected.

The types of garbage collectors in Java include Serial Garbage Collector, Parallel Garbage Collector, CMS (Concurrent Mark-Sweep) Garbage Collector, and G1 (Garbage-First) Garbage Collector.

'gc()' is a hint to the garbage collector to run, while 'System.gc()' is a method that suggests to the JVM to run the garbage collector, but the actual execution is at the discretion of the JVM.

Generational Garbage Collection is based on the observation that most objects become unreachable shortly after they are created. It divides the heap into two main areas: the Young Generation and the Old Generation.

The Eden Space is the part of the Young Generation where new objects are initially allocated. Objects surviving garbage collection in Eden are moved to the Survivor Spaces.

The Survivor Spaces (S0 and S1) in the Young Generation are used to hold objects that survive one garbage collection cycle in the Eden Space. Objects can be promoted to the Old Generation from the Survivor Spaces.

Garbage collection is the process of automatically identifying and reclaiming unused memory, while a memory leak occurs when the application fails to release memory that is no longer needed, leading to increased memory consumption over time.

The 'OutOfMemoryError' is an exception thrown when the Java Virtual Machine (JVM) runs out of memory. It can occur if the garbage collector is unable to free up enough memory to satisfy the memory allocation request.

Garbage collection ergonomics involves the JVM automatically tuning garbage collection parameters based on the characteristics of the application, such as heap size, pause time goals, and allocation rates.

The '-Xmx' option sets the maximum heap size, while the '-Xms' option sets the initial heap size. Properly configuring these options can impact garbage collection performance and overall application memory usage.

Garbage Collection Roots are objects that are considered to be reachable at all times and serve as starting points for the garbage collector. Examples include local variables, active threads, and static variables.

Garbage collection performance can be monitored using tools like VisualVM, JConsole, and other profiling tools. Analyzing garbage collection logs and metrics helps identify issues and optimize performance.

The 'CMSInitialMarkPause' is the initial phase of the CMS (Concurrent Mark-Sweep) garbage collector. During this phase, the collector identifies and marks live objects in the Old Generation while briefly pausing application threads.