Java Garbage Collection Interview Questions and Answers
Intermediate / 1 to 5 years experienced level questions & answers
Ques 1. Explain the purpose of the finalize() method.
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.
Ques 2. Name the different types of garbage collectors in Java.
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.
Ques 3. Explain the difference between 'gc()' and 'System.gc()' in Java.
'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.
Ques 4. Explain the concept of Generational Garbage Collection.
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.
Ques 5. What is the Eden Space in the Young Generation of the Java heap?
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.
Ques 6. Explain the purpose of the Survivor Spaces in the Young Generation.
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.
Ques 7. What is the difference between garbage collection and memory leak?
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.
Ques 8. What is the 'OutOfMemoryError' in Java, and how is it related to garbage collection?
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.
Ques 9. Explain the concept of garbage collection ergonomics in Java.
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.
Ques 10. What is the role of the '-Xmx' and '-Xms' JVM options in garbage collection?
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.
Ques 11. Explain the concept of 'Garbage Collection Roots' in Java.
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.
Ques 12. How can you monitor and analyze garbage collection performance in Java?
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.
Ques 13. What is the 'CMSInitialMarkPause' phase in the CMS garbage collector?
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.
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