Core Java - Interview Questions and Answers for 'Core Java' | Search Interview Question

Interview Questions and Answers - Order By Newest

Q581. Who invokes a thread's run method ?

Ans. After a thread is started using a call to start method, JVM invokes the thread’s run method when the thread is initially executed.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve threads thread run method Asked in 1 Companies}

Q582. What is nested interface?

Core Java

Ans. Interface that is declared inside the interface or class, is known as nested interface. It is static by default.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve interface nested interface intermediate}

Try 1 Question(s) Test

Q583. What kind of thread is garbage collection thread ?

Core Java

Ans. Daemon thread

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve garbage collection intermediate}

Try 2 Question(s) Test

Q584. What is the difference between the Reader/Writer java.io hierarchy and the Stream class hierarchy?

Core Java

Ans. The Reader/Writer hierarchy is character oriented, whereas the Stream class hierarchy is byte oriented.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java io streams intermediate}

Q585. What is an IO Filter ?

Core Java

Ans. It's an object that reads from one stream and writes to another.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve java io io filter intermediate}

Q586. Difference between shallow copy and object cloning ?

Core Java

Ans. Shallow copy is one of the way for object cloning, other being deep copy.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve cloning shallow copy object cloning basic}

Q587. What is Shutdown hook ?

Core Java

Ans. Shutdown hook is a thread that is invoked before the JVM is shut down. we can use it perform resource cleaning task.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve shutdown hook jvm}

Try 1 Question(s) Test

Q588. how to access the methods of an inner class?

Core Java

Ans. It depends on the type of inner class

To access non static inner class method

new OuterClass().new InnerClass().getMethod();

To access static method of static inner class

new OuterClass.InnerClass().getMethod();

Sample Code for inner class

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve inner classes nested aclasses Asked in 1 Companies Intermediate frequent}

Q589. Which memory segment holds String Pool in Java ?

Core Java

Ans. String Pool resides in runtime constant Pool which is a part of Heap memory segment.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string pool memory management Expert rare}

Q590. What are the cursors available in Java ?

Core Java

Ans. Enumeration
Iterator
List iterator

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve cursors iterator}

Q591. How can be restrict creation of more than n objects in Java ?

Core Java

Ans. We can follow the same design which we follow in singleton Classes. We can have a static counter that will keep the count of number of objects already created, We can keep the constructor private and being called through the static method. We can keep incrementing the counter before calling the constructor and put a check to call only if it's lesser than n.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q592. Do you feel that its useless to define hashCode method for a class ?

Core Java

Ans. Yes its useless if we are not going to use its objects within Hash collection, For example - HashSet , HashMap. HashCode is used internally by these collections for Search.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve hashcode hash collections search}

Q593. What is a class and object ?

or

How would you explain a fresher the concept of class and object in simple terms ?

Core Java

Ans. Class is a template using which objects are created in memory. It's kind of a mold using which objects with body / state are made.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve class object class vs object Asked in 4 Companies basic frequent}

Q594. Explain dot(.) operator ?

Core Java

Ans. Its used to access the object properties using the object reference or class properties using the Class Name. Moreover its used to access the classes and Interfaces of a package.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve operators}

Q595. Does Java supports Default arguments ?

Core Java

Ans. No

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve}

Q596. Can we have only try block in java ?

Core Java

Ans. No, It should be followed by either catch or finally.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve try exception handling}

Q597. What is memory leak ? How Java helps countering memory leaks compared to C++ ?

Core Java

Ans. Memory Leak is a situation wherein we have a reserved memory location but the program has lost its reference and hence has no way to access it.

Java doesn't have concept of Pointers, Moreover Java has concept of Garbage collection that frees up space in heap that has lost its references.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve memory leak garbage collection intermediate frequent}

Q598. What are the benefits of creating immutable objects ?

Core Java

Ans. 1. Security and Safety - They can be shared across multiple threads as they are thread safe. Moreover, it protects then from bad state due to interception by the other code segment. One such problem due to mutability and access by alternate code segment could be the change of hash code and then the impact on its search with hash collections.

2. Reuse - In some cases they can be reused as only one copy would exist and hence it can be relied upon. For example - String Pool

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve immutable immutability objects Asked in 1 Companies Intermediate frequent}

Q599. What is the difference between

File f = new File("homexyz.txt");

and

File f = File.createTempFile("xyz",".txt","home"); ?

Core Java

Ans. First will not create physical file in storage whereas the second will.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve file handling File.createTempFile file handling intermediate rare}

Q600. What is an applet ?

Core Java

Ans. Applet is a J2EE component or a tiny application that gets executed in a widget engine ( like browser )

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve applet}

Q601. What are callback methods ?

Core Java

Ans. Component methods called by the container to notify the component of the events

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Asked in 1 Companies}

Q602. How and Why Strings are interned in Java ?

Core Java

Ans. String class has a public method intern() that returns a canonical representation for the string object. String class privately maintains a pool of strings, where String literals are automatically interned.

these are automatically interned so as to have efficient String comparison using == operator instead of equals which is usually slower.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string string pool string intern Asked in 1 Companies}

Q603. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
   public static void main(String[] args){
      System.out.println(BaseInterface.i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. It will print 4 because member elements of an interface are implicitly static and hence the concept of overriding doesn't work.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve interfaces coding code extending interfaces diamond interfaces Asked in 1 Companies intermediate}

Q604. What will be the output of following code ?

Base Interface

public interface BaseInterface {
   int i = 4;
}

Derived Interfaces

public interface DerivedInterface1 extends BaseInterface{
   int i = 5;
}

public interface DerivedInterface2 extends BaseInterface{
   int i=6;
}

Implementing Class

public class Class implements DerivedInterface1,DerivedInterface2 {
int i=10;

public static void main(String[] args){
      System.out.println(new Class().i);
   }
}

What will be the output upon executing main and Why ?

Core Java

Ans. 10

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve interfaces coding code intermediate}

Q605. What is the difference between compilation and decompilation ?

Core Java

Ans. Compilation is the process of converting Java source files to class files which can be executed by the Java runtime environment whereas Decompilation is the process of converting class files back to the Java Source code.

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve compilation vs decompilation compiler vs decompiler}

Q606. Write a class / program that takes few numbers from the input and then output the average ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      List<Integer> collector = new ArrayList();

      Scanner scanner = new Scanner(System.in);
      int x = scanner.nextInt();
      while(x != 0){
         collector.add(x);
         x = scanner.nextInt();
      }
      System.out.println(collector.stream().collect(Collectors.averagingInt(p->((Integer)p))));
   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve coding code collector streams Collectors.average Asked in 1 Companies}

Q607. Write a program to check is a string is substring of another ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      if(string1.indexOf(string2) >= -1){
         System.out.println("string2 is sub string of string1");
      } else {
         System.out.println("string2 is not sub string of string1");
      }
   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string coding code}

Q608. Write a Program to check number of occurrences of one string within another ?

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String string1 = "Hello I am Jack. I live in United States. I live in california state.";

      String string2 = "I live in";

      int startIndex = 0;
      int endIndex = string1.length()-1;

      int countNoOfOccurences = 0;

      String remainingString = string1;

      while(startIndex < endIndex){
         if(remainingString.indexOf(string2) != -1){
            countNoOfOccurences++;
            startIndex = remainingString.indexOf(string2) + string2.length();
            remainingString = remainingString.substring(startIndex);
         } else {
            break;
         }
      }

      System.out.println(countNoOfOccurences);
   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve string code coding Asked in 2 Companies}

Q609. Write a Program to check if string is a Colidrome ?
(Colidrome is a word that has n alphabets followed by the reverse of the n alphabets, for ex - mallom)

Core Java

Ans.
public class Class {
   public static void main(String[] args) {
      String str = "mallam";
      String firstHalf = str.substring(0, str.length() / 2);
      String secondHalf = str.substring(str.length() / 2);

      if (firstHalf.equals(new StringBuilder(secondHalf).reverse().toString())) {
         System.out.println("It's a Colidrome");
      } else {
         System.out.println("It's not a Colidrome");
      }
   }
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve Colidrome String Code Coding Asked in 1 Companies}

Q610. Write a program in Java that prints the numbers from 1 to 100. But for multiples of three print Fizz instead of the number and for the multiples of five print Buz. For numbers which are multiples of both three and five print FizzBuzz

Core Java

Ans. public class Class{
public static void main(String[] args){
for(int i=1;i<= 100;i++){
if(i%3 == 0){
if(i%5 == 0){
System.out.println("FizzBuzz");
}
System.out.println("Fizz");
} else if(i%5 == 0){
System.out.println("Buzz");
} else {
System.out.println(i);
}

}
}
}

Help us improve. Please let us know the company, where you were asked this question :

_{Like Discuss Correct / Improve code coding Asked in 2 Companies}

Search Interview Questions

Help us and Others Improve. Please let us know the questions asked in any of your previous interview.