Garbage Collection

Question 1

What is Garbage Collection in

Java?

Answer 1

Java has an internal mechanism called Garbage collection to reclaim the memory of unused projects at run time.

Garbage collection is also known as automatic memory management.

Question 2

Why Java provides Garbage Collector?

Answer 2

In Java, there are no pointers. Memory management and allocation is done by JVM. Since memory allocation is automated, after some time JVM may go low on memory. At that time, JVM has to free memory from unused objects.

To help with the process of reclaiming memory, Java provides an automated process called
Garbage Collector.

Question 3

How does Garbage Collection work in Java?

Answer 3

Java has an automated process called Garbage Collector for Memory Management. It is a daemon in JVM that monitors the
memory usage and performs memory cleanup.

Once JVM is low on memory, GC process finds the unused objects that are not referenced by other objects. These unused objects are cleaned up by Garbage Collector daemon in JVM.

Question 4

When does an object become eligible for Garbage Collection in Java?

Answer 4

An object can be Garbage Collected by JVM, if it is not reachable. There are two cases for deciding eligibility of objects for Garbage
Collection:

1. An Object/instance that cannot be reached by a live thread.
2. A set of circularly referenced instances that cannot be
   reached by any other instance outside that set.

Question 5

Why do we use finalize() method

in Java?

Answer 5

Java provides finalize() method to perform any cleanup before
Garbage Collection. This method is in Object class, and it is
invoked by JVM internally. Developers are free to implement this
method for any custom cleanup in case of Garbage Collection.
If an Object is not Garbage Collected, then this method may not be
called.
This method is never invoked more than once by JVM.

Question 6

What are the different types of References in Java?

Answer 6

In Java, there are four types of references:

1. Strong Reference
2. Soft Reference
3. Weak Reference
4. Phantom Reference

Question 7

How can we reference an

unreferenced object again?

Answer 7

We can provide implementation in finalize() method to reference and unreferenced object. For an unreferenced object, finalize()
method is called at the time of Garbage Collection. At this time, Object can pass its reference ‘this’ to finalize() method and revive
itself.

Question 8

What kind of process is the

Garbage collector thread?

Answer 8

Garbage Collection is a Daemon process in JVM. It is an internal
process that keep checking Memory usage and cleans up the
memory.

Question 9

What is the purpose of the Runtime class?

Answer 9

The purpose of the Runtime class is to provide access to the Java
Runtime system. This class provides certain important methods like:
1. Runtime.freeMemory() – This method returns the value of
free memory in JVM
2. Runtime.maxMemory() - This method returns the value of
maximum memory that JVM can use.
3. Runtime.gc() – This method can invoke garbage collection.

Question 10

How can we invoke an external process in Java?

Answer 10

Java provides the method Runtime.getRuntime().exec() to invoke an
external process from JVM.

Question 11

What are the uses of Runtime class?

Answer 11

Runtime class in Java provides following benefits:
1. It allows to read data via key board
2. It can use system properties and environment variables
3. It helps in running non-java programs from within a java
application.