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Q1801. What will be the output of following code

Integer x = 1;
Integer y = 2;
System.out.println(x == y);

What if you change 1 to "1" and Integer to String?

Core Java

Ans. It will print "true" with integers as well as strings. The reason is "Integer constant pool" and "String pool"

String pool maintains pool of string literals. When a string literal is used for the first time, a new string object is created and is added to the pool. Upon it's subsequent usage , the reference for the same object is returned. Similarly java uses integer constant pool.

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Q1802. What are the advantages and disadvantages of using lock classes from java.util.concurrent.locks vs. synchronized methods ?

Core Java

Ans. http://www.devinline.com/2015/10/Lock-Vs-synchronized-in-java.html

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Q1803. What is the difference between CountingSemaphore and a CountDownLatch?

Operating System

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Q1804. What is the trade off between using Collections.synchronizedList() on an ArrayList and a CopyOnWriteArrayList?

Core Java

Ans. Synchronized List locks the whole list to provide synchronization and thread safety during the read or write operation, while, CopyOnWriteArrayList doesn’t lock the whole list during these operations.
The CopyOnWriteArrayList class works according to its name i.e. copy-on-write which performs different actions for reading and write operations. For every write operation (add, set, remove, etc), it makes a new copy of the elements in the list. and for the read operations (get, iterator, listIterator, etc), it works on a different copy. So there is no additional overhead during a read operation and its read operation is faster than Collections.SynchronizedList(). Thus, COWAL is better for reading operation than Synchronized List.

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Q1805. Tell me about your greatest accomplishment?

General

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Q1806. What is your role in your current organization?

General

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Q1807. Given a string with multiple opening and closing brackets, determine if the string is valid or not ( to see if the string has all closing brackets for each opening bracket ) ?

Core Java

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Q1808. Given a string and index for the opening bracket, find the index of matching closing bracket.

Core Java

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Q1809. How can we destroy an object ?

Core Java

Ans. We cannot explicitly initiate destruction of an object as no destroy method is available in java. Only Garbage collection can destroy an object.

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Q1810. When does an object cleaned or destroyed by garbage collection ?

Core Java

Ans. When it is no longer referenced or it looses all references which were earlier pointing to it.

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Q1811. What will be result of following code and why

Integer int1 = 1;
Integer int2 = 1;
String str1 = new String("str");
String str2 = new String("str");
String str3 = "str";
String str4 = "str";

System.out.println(int1 == int2);
System.out.println(str1 == str2);
System.out.println(str3 == str4);

Core Java

Ans. true
false
true

Just like Strings, java maintains an integer constant pool too. So 1 will be maintained in integer constant pool and hence reference int2 will point to same integer in pool.

String pool is only for string literals ( defined by "" ) and not for newly created objects and hence str1 == str2 will return false as they are separate objects in memory.

String pool is used for storing string literals so that they can be reused and str3 and str4 will point to same string literal in string pool.

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Q1812. Does a Junit without any assertions makes any sense ?

Junit

Ans. Yes, If we are testing a code segment to check if throws / doesn't throw an exception. Moreover while testing void methods, we may just verify and not use assert.

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Q1813. If we have to maintain a value "7" denoting "number of days in a week" as constant variable, Which of the following is the best constant name and Why ?

SEVEN
NUMBER_OF_DAYS_IN_WEEK
NUMBER_OF_DAYS_IN_WEEK_7

Core Java

Ans. NUMBER_OF_DAYS_IN_WEEK

Constant should be such that it uniquely identifies the value it holds and context of the value. SEVEN uniquely identifies the value but doesn't express the context.

Though NUMBER_OF_DAYS_IN_WEEK and NUMBER_OF_DAYS_IN_WEEK_7 makes sense in terms of unique value identification and context but 7 at the end of constant name appears useless as all weeks have 7 days and hence it's the only value it can hold. If it would have been "number of days in a month", it would have made sense to include number of days at the end like

NUMBER_OF_DAYS_IN_MONTH_30
NUMBER_OF_DAYS_IN_MONTH_31
NUMBER_OF_DAYS_IN_MONTH_27
NUMBER_OF_DAYS_IN_MONTH_28

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Q1814. If we have to maintain a value "31" denoting "number of days in a month" as constant variable, Which of the following is the best constant name and Why ?

THIRTY_ONE
NUMBER_OF_DAYS_IN_MONTH
NUMBER_OF_DAYS_IN_MONTH_31

Core Java

Ans. NUMBER_OF_DAYS_IN_MONTH_31

Constant should be such that it uniquely identifies the value it holds and context of the value. THIRTY_ONE uniquely identifies the value but doesn't express the context. NUMBER_OF_DAYS_IN_MONTH expresses the context but doesn't specify the value clearly as different month can have different number of days.

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Q1815. Would you consider creating a constant name for "null" ?

Core Java

Ans. Objective of constant variable is to provide a context to the value and provide a single point of change. In terms of context, i don't see much need for having constant name for null as null is already self explanatory. In terms of providing single point of change, it doesn't make much sense as it would necessitate that all such placeholders either hold null or a common value.

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Q1816. Where does database stored procedures gets stored ?

Database

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Q1817. What is a platform ? Is Java a Software or Hardware platforms ?

Core Java

Ans. Platform is the environment in which a program runs. Java provides a software platform for running JVM based applications and programs.

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Q1818. What is a blank final variable ? Can we initialize a blank final variable ?

Core Java

Ans. A final variable that is not initialized while declaration is a blank final variable.

Yes, we can initialize it within a constructor.

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Q1819. What is the purpose of String Pool ? Don't you think it's a performance overhead to have unnecessary check for string in string pool ?

Core Java

Ans. String Pool makes Java more memory efficient by providing a reusable place for string literals. It might be a little performance inconvenience but results in good amount memory saving.

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Q1820. What is equals method in Java ?

Core Java

Ans. equals is the method of Object class that is overridden by the classes to specify object equality criteria.

As every class extends Object class, the default implementation of equals is carried to them. Default implementation specified in the Object class is that two objects are treated equal if they are same.

i.e

Object x = new Object();
Object y = new Object();
x.equals(y); // false
x=y;
x.equals(y); // true

i.e x.equals(y) if only x==y

Now every class has the option to specify their object equality by overriding equals method. For example - String class has implemented in a manner if the string value contained in them is exactly same.

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Q1821. What is void in Java ?

Core Java

Ans. void is a return type which indicates that the method returns nothing but returns the control to the line next to the method call. All methods need to have a return type and hence a method returning nothing needs to be declared void.

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Q1822. Does all methods need to have a return type ? Is it applicable to constructors too ?

Core Java

Ans. All methods are not expected to return something but Yes, all methods are expected to have a return type. If a method returns nothing, it can be declared with the return type void.

Constructors are not expected to have any return types , not even void.

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Q1823. What is the difference between the 2 methods in Java ?

Class BuggyBread {

BuggyBread(){
}
void BuggyBread(){
}
}

Core Java

Ans. BuggyBread method without any return type is the constructor which get's called upon object creation whereas BuggyBread method with return type of void is just another method that needs to be called explicitly for it's invocation.

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Q1824. Is this constructor overloading ?

What is the difference between the 2 methods in Java ?

Class BuggyBread {

BuggyBread(){
}
void BuggyBread(int x){
}
}

Core Java

Ans. No, first method is a constructor whereas the second method is just a normal method. There is no way a constructor can be called explicitly and hence all explicit calls to BuggyBread() would result in compilation error.

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Q1825. Can we call a constructor explicitly , just like a method ?

Core Java

Ans. No we cannot call a constructor like that.

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Q1826. What is the difference between reference and object ?

Core Java

Ans. Object is an entity in Java , i.e which has a state ( instance variables ) and methods attached to it ( static or non static , through class definition ). References are the identifiers that are used to point to objects.

For example -

Employee emp = new Employee();
emp = new Employee();

In this code, emp is the reference that gets assigned to the new object created by the new operator. In the second line , we have assigned the same reference to another object. So with these 2 lines of code, we have 2 objects in memory with reference emp now pointing to second object.

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Q1827. Make the following class immutable

public class Employee {

   private long employeeId;

   private String employeeName;

   public long getEmployeeId() {
      return employeeId;
   }

public void setEmployeeId(long employeeId) {
      this.employeeId = employeeId;
   }

   public String getEmployeeName() {
      return employeeName;
   }

public void setEmployeeName(String employeeName) {
      this.employeeName = employeeName;
   }
}

Core Java

Ans. public class Employee {

   private long employeeId;

   private String employeeName;

   public Employee(long employeeId,String employeeName){
      this.employeeId = employeeId;
      this.employeeName = employeeName;
   }

   public long getEmployeeId() {
      return employeeId;
   }

   public long getEmployeeName() {
      return employeeName;
   }
}

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Q1828. What is AWS or Amazon Web Services ?

Amazon Web Services (AWS)

Ans. These are the platforms or set of services provided by Amazon for cloud services , database storage , content delivery and other business applications and solutions.

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Q1829. What are the different layers of cloud computing ?

Infrastructure

Ans. Paas - Platform as a service
Iaas - Infrastructure as a service
Saas - Software as a service

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Q1830. What is a pull request ?

GIT

Ans. It's a facility to shout out your code changes to other collaborators before merging them to the main repository. For example - one may like to have code changes reviewed between his branch and master before merging it to master. So he can open a pull request with the difference between branch and master, get it reviewed and then merge it to master.

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