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

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Q1001. Write a Program to print pattern like following

*
**
***
****
*****
******
*******
********
*********
**********

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=10;x++){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.println("");
      }
   }
}

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Q1002. Write a Program to print pattern like following

*_**_***_****_*****_***************

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.print("_");
      }

      for(int x=5;x>=1;x--){
         for(int y=1;y<=x;y++){
            System.out.print("*");
         }

         System.out.print("");
      }
   }
}

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Q1003. Write a Program to print numbers like following

1
12
123
1234
12345

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print(y);
         }

         System.out.println(" ");
      }
   }
}

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Q1004. Write a Program to print numbers like following

1
22
333
4444
55555

Core Java

Ans. public class BuggyBread {
   public static void main(String args[]) {
      for(int x=1;x<=5;x++){
         for(int y=1;y<=x;y++){
            System.out.print(x);
         }

         System.out.println(" ");
      }
   }
}

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Q1005. Difference between concurrentHashMap and HashTable ?

Core Java

Ans. HashTable locks the complete collection to provide synchronization whereas ConcurrentHashMap only locks segments to achieve synchronization and hence better efficient and faster.

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Q1006. isnt the use of HashTable and ConcurrentHashMap the same, i.e providing synchronized map collection ?

Core Java

Ans. Yes, they both aim at providing synchronized access to the Map collection. The only difference is in their implementation. ConcurrentHashMap came after HashTable and hence technically more efficient as it doesn't lock the complete map while accessing it.

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Q1007. Upon compiling the following class, What .class files will get created

public class OuterClass{
class InnerClass{
}
}

Core Java

Ans. OuterClass.class AND OuterClass$InnerClass.class

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Q1008. Write a Program to validate an email address

Core Java

Ans. public class Class{
public static void main(String[] args){
String str = "xyz@123.com";

if(!str.contains("@") && !str.contains(".") && (str.indexOf('.') < str.indexOf('@'))){
System.out.println("Not a Valid Email Address");
}
}
}

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Q1009. Write a Program to validate if a particular character occurs after another in a string

Core Java

Ans. public class Class{
   public static void main(String[] args){
      String str = "xyz123.co@m";

      if(str.indexOf('.') < str.indexOf('@')){
         System.out.println("Not a Valid Email Address");
      }
   }
}

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Q1010. Write a Program to find the missing integer in an array of consecutive numbers?

Core Java

^{This question was recently asked at 'Knight Capital'.This question is still unanswered. Can you please provide an answer.}

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Q1011. How to find the median number in an array of integers ?

Core Java

Ans.

Arrays.sort(numArray);
double median;
if (numArray.length % 2 == 0)
median = ((double)numArray[numArray.length/2] (double)numArray[numArray.length/2 - 1])/2;
else
median = (double) numArray[numArray.length-1/2];

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Q1012. Ho do you share / transfer variables between JSP pages ?

Java EE

^{This question was recently asked at 'UC Davis'.This question is still unanswered. Can you please provide an answer.}

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Q1013. Write a Java program to print 10 random numbers between 1 to 100?

Core Java

^{This question was recently asked at 'karya technology'.This question is still unanswered. Can you please provide an answer.}

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Q1014. Why don't Java objects have destructors ?

Core Java

Ans. Java manages memory using built-in garbage collector

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Q1015. What is the difference between && and & in Java ?

Core Java

Ans. && is a Logical whereas & is a bitwise operator

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Q1016. Why is it important to close files and streams ?

Core Java

Ans. Optimizing Resource utilization. When you open a file using any programming language , that is actually a request to operating system to access the file. When such a request is made , resources are allocated by the OS. When you gracefully close those files, those resources are set free.

In Java if you don’t close the streams and files, Garbage collection identifies the open files which have lost the reference and hence will close them.

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Q1017. Write a method / program that will determine if the parenthesis are balanced in a given string.

Core Java

Ans. https://www.geeksforgeeks.org/check-for-balanced-parentheses-in-an-expression/

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Q1018. What are the core OOPs concepts ?

Core Java

Ans. Abstraction, Encapsulation, Polymorphism , Composition and Inheritance

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Q1019. How are the concept of Association related to Composition and Inheritance ?

Core Java

Ans. Composition and Inheritance are the different types of Associations for Classes.

Composition is a has-a association between classes.
Inheritance is a is-a association between classes.

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Q1020. What is an execution engine within JVM ?

Core Java

Ans. Execution engine contains interpreter and JIT compiler, which covert byte code into machine code.

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Q1021. What are some of the Java Naming conventions ?

Core Java

Ans. 1. Class name should be a noun and should start with capital case character.

2. Interface Name should be an adjective and should start with capital case character.

3. Method and Variable names should follow lower camel case notation.

4. package name should be all lower case.

5. constant variables (static final) should be all capital case.

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Q1022. write program to do matrix multiplication

Core Java

^{This question was recently asked at 'Kony Labs'.This question is still unanswered. Can you please provide an answer.}

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Q1023. How do threads share information ?

Core Java

Ans. Through common memory area.

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Q1024. What is Substitutability in Java ?

Core Java

Ans. Substitutability means that the type of the variable does not have to exactly match with the type of the value assigned to that variable. For example - Object reference of Parent object can hold derived object.

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Q1025. What is the precedence of operators in Java ?

Core Java

Ans. http://introcs.cs.princeton.edu/java/11precedence/

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Q1026. Can we override abstract methods ?

Core Java

Ans. Abstract methods are the methods that need to be overridden in the derived class ( either as implementing method or again abstract method ) so it's not only allowed but its required to override abstract method in the derived class.

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Q1027. Can we override an abstract method with abstract method in the derived class ?

Core Java

Ans. Yes, but in that case the derived class itself should be abstract. We cannot have an object of a class without definition for the method which has been declared abstract in the parent.

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Q1028. Given array of integers, find first two numbers that adds up to 10.

Core Java

^{This question was recently asked at 'Amazon'.This question is still unanswered. Can you please provide an answer.}

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Q1029. Write a program to reverse words of a sentence.

Core Java

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Q1030. how to get most significant bit from a byte?

Core Java

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