Interview questions on JVM for experienced

June 10, 2023

 Part 5

Interview questions on JVM for  experienced covered in this post:

    Interview questions on JVM for experienced


        How Stack and Heap correlated to each other while creating object?

    -          JVM has bifurcated memory into two parts. The first one is stack memory and the second one is heap memory.

    -          Stack memory is mainly used for storing the order of method execution and local variables.

    -          Heap memory is mainly used for storing actual objects created with a new keyword.

    -          Stack and heap memory are correlated while managing the objects life cycle. Once created object on heap memory will be referenced to the reference variable which is stored on stack memory.

    -          Please refer to the below diagram.


        What is the difference between Stack Memory and Heap Memory?

     

    Stack Memory

    Heap Memory

    1.

    Stack memory is mainly used for storing the order of method execution and local variables.

    Heap memory is mainly used for storing actual objects created with a new keyword.

    2.

    Stack memory works with the LIFO mechanism.

    There is no mechanism to allocate and deallocate the memory in heap.

    3.

    Stack variables are visible only to the owner thread.

    Objects are visible to all threads.

    4.

    We can increase stack memory size by using –XSS parameter.

    We can modify the size of heap memory by using Xms and –Xmx.

    5.

    If the stack gets full and still trying to add more elements in it then it will throw StackOverFlowError.

    If JVM gets full then it will throw OutOfMemoryError.

     

     

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        What the Strong reference, Weak reference, phantom reference and soft reference?

    -          Strong Reference - is a kind of reference, which makes the referenced object not eligible for GC. builder classes. eg - StringBuilder

    -          Weak Reference - is a reference that is eligible for GC.

    -          Soft Reference - is a kind of reference whose object is eligible for GC until memory is available. Best for image cache. It will hold them till the memory is available.

    -          Phantom Reference - is a kind of reference whose object is directly eligible for GC. Used only to know when an object is removed from memory.

     

        What are the steps JVM needs to take while loading class in memory?

    -          Load - The class file is loaded to JVM memory.

    -          Verify - Verifies that the class follows the Java language and JVM specifications.

    -          Resolve - Change symbolic references to direct references.

    -          Initialize - Initializes class variable and static variables.

     

        What are the components of JVM or Explain Java Architecture?

    -          Please refer to the below diagram first.

    -          JVM’s prime responsibility is to convert byte code into machine code.

    -          JVM load the code into memory and verifies it and execute the code and provides a run-time environment.

    -          Please refer to the below diagram for java architecture.



    -          Following are the details of JVM components.

    1.       ClassLoader: ClassLoader is used to load the classes in the main memory. JVMs primary task is to load the classes into memory.

    2.       Method Area: In the method area class data is stored during the code’s execution. Class method area holds the information of static variables, static methods, static blocks and instance methods.

    3.       Heap: Heap memory is mainly used for storing actual objects created with a new keyword. There is no mechanism to allocate and deallocate the memory in heap. We can modify the size of heap memory by using Xms and –Xmx. If JVM gets full then it will throw OutOfMemoryError.

    4.       Stack: Stack memory is mainly used for storing the order of method execution and local variables. Stack memory works with the LIFO mechanism. We can increase stack memory size by using –XSS parameter. If the stack gets full and still trying to add more elements in it then it will throw StackOverFlowError.

    5.       Native Stack: This contains the data about native methods. The Methods which are written other than java language are called Native methods.

    6.       Execution Engine: This is the main part of JVM. Its main task is to execute the byte code and execute the java classes. There are three components in the Execution engine.

    §  Interpreter: The interpreter sequentially executes the code. The interpreter interprets the code continuously line by line.

    §  JIT Compiler: JIT stands for Just-In-time compiler. The performance of the JIT compiler is superior to Interpreter. We can replace the JIT compiler with an Interpreter.

    §  Garbage Collector: Garbage collector is used to removing the unreferenced objects and reclaim the memory.

    7.       Native Interface: Native interface is a mediator between java methods and native libraries.


    • Java interview questions and answers all MNC - Click here
    • Basic core java interview questions and answers for freshers - Click here
    • Core java interview questions for 3 years experience - Click here
    • Core java interview questions and answers for 3-5 years exp - Click here
    • Core java interview questions and Answers for 5 - 7 Years exp - Click here
    • Basic Java Interview Questions and Answers - Click here
    • Java interview questions and answers on oops - Click here
    • Java interview questions and answers on Strings - Click here
    • Java interview questions on exception handling - Click here
    • Interview questions on multithreading in java for experienced - Click here
    • Interview questions on serialization in java for experienced - Click here

    • Interview questions on inner class in java for experienced - Click here
    • Interview questions on Collections in java for experienced - Click here

    Upcoming questions in next post:


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