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Interview Questions and Answers - Order By Rating

   
 Q31. Difference between static vs. dynamic class loading?Core Java
Ans. static loading - Classes are statically loaded with Java new operator.

dynamic class loading - Dynamic loading is a technique for programmatically invoking the functions of a class loader at run time.

Class.forName (Test className);

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 Q32. What are strong, soft, weak and phantom references in Java ?Core Java
Ans. Garbage Collector wont remove a strong reference.

A soft reference will only get removed if memory is low.

A weak reference will get removed on the next garbage collection cycle.

A phantom reference will be finalized but the memory will not be reclaimed. Can be useful when you want to be notified that an object is about to be collected.

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 Q33. Name few tools for probing Java Memory Leaks ?
Ans. JProbe, OptimizeIt

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   Like         Discuss         Correct / Improve     java   tools   jvm   memory management   memory leaks   jprobe   optimeit   architecture   technical lead


 Q34. Which memory areas does instance and static variables use ?Core Java
Ans. instance variables and objects are stored on heap and the references are stored on stack whereas static variables are stored in the method area of heap.

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   Like         Discuss         Correct / Improve     java   jvm   memory management   memory   heap   stack

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 Q35. What is PermGen or Permanent Generation ?Core Java
Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.

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   Like         Discuss         Correct / Improve     java   jvm   memory management   permgen   permanent generation   advanced   architecture     Asked in 9 Companies      expert


 Q36. What is metaspace ?Core Java
Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.

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 Q37. Can we call the garbage collector explicitly ?Core Java
Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.

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 Q38. What are different ways to create String Object? Explain.Core Java
Ans. There are total six ways

1. literals

When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.

2. new keyword

When we use new operator, JVM creates the String object but dont store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.

3. string buffer
4. string builder
5. System.out.println
6. char to string




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   Like         Discuss         Correct / Improve     java   string class   string   jvm   memory management   string pool     Asked in 5 Companies      basic        frequent

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 Q39. How substring() method of String class create memory leaks?Core Java
Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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 Q40. Name few classes java provides for memory management ?
Ans. http://www.buggybread.com/2015/01/java-memory-classes-and-interfaces.html

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 Q41. Difference between Stack and Heap memory ?Core Java
Ans. Stack memory areas is used to hold method and local variables while objects are always allocated memory in the heap. The heap memory is shared between multiple threads whereas Stack memory isn't.

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 Q42. What will happen if we don't have termination statement in recursion ?
Ans. Function call allocates a stackframe in stack. Every stackframe will use some memory to store local variables, parameters and to remember return address. Without terminating condition stackframes will keep consuming memory from stack and eventually program will result in stackoverflow error.

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   Like         Discuss         Correct / Improve     recursion   break statement  break  stackoverflow exception  stackoverflow  memory management  memory  exceptions


 Q43. Function variables are kept in ..Core Java
a. Stack
b. Heap
c. Both Stack and Heap
d. None of them

Ans.a. Stack

 Q44. Which memory segment holds String Pool ?Core Java
a. Stack
b. Heap
c. Code Segment
d. Class Segment

Ans.b. Heap

 Q45. In this code

public class BuggyBread1{
   private static String staticVariable = "static Variable";
   
   private String instanceVariable = "instance Variable";
   
   public static void main (String args[]) {
String localVariable = "local Variable";
}
}

Where will the value 'static Variable' be stored ?
Core Java
a. Stack Memory Segment
b. Heap Memory Segment
c. Runtime Constant Pool within Heap Segment
d. Code Segment

Ans.c. Runtime Constant Pool within Heap Segment

 Q46. In this code

public class BuggyBread1{
   private static String staticVariable = "static Variable";
   
   private String instanceVariable = "instance Variable";
   
   public static void main (String args[]) {
String localVariable = new String("local Variable");
}
}

Where will the value 'local Variable' be stored ?
Core Java
a. Stack Memory Segment
b. Heap Memory Segment
c. Runtime Constant Pool within Heap Segment
d. Code Segment

Ans.a. Stack Memory Segment

 Q47. In this code

public class BuggyBread1{
   private static String staticVariable = new String("static Variable");
   
   private String instanceVariable = "instance Variable";
   
   public static void main (String args[]) {
String localVariable = "local Variable";
}
}

Where will the value 'static Variable' be stored ?
Core Java
a. Stack Memory Segment
b. Heap Memory Segment
c. Runtime Constant Pool within Heap Segment
d. Code Segment

Ans.b. Heap Memory Segment

 Q48. Which of following memory segment is cleaned by Garbage Collection Mechanism ?Core Java
a. Stack
b. Heap
c. Code
d. Cache

Ans.b. Heap

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