How Hashmap works internally in java

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Difference between equals() and ==

Hi all , these days i\'m about to write a post on very fashionable interview question that is what\'s the difference between equals and == .It is asked in every object familiarised language interview whether or not its Java or ASP.NET For this you must apprehend the essential difference between each .

1. The very first difference in both is that equals ()  is a  method == is an operator . this can be the terribly basic factor you must understand equals and ==
As in java there\'s no concept of operator overloading thus we cannot modify the behavior of == operator.

2. “= = “operator : “= =” is a binary operator used to compare both primitive sorts like int ,Boolean and objects .
While examination primitive sort its works properly and returns right output
For example :


int a=1;
int b=2;

if(a==b)

else


Output : Not Equal;

While examination 2 objects using “==” ,a problem arises is that “= =” checks reference of each objects not price and returns output correspondingly .

This can be illustrated with the assistance of associate example :










String variable1=new String(“First”);
String variable2=new String(“First);

If(variable1==variable2)

else


Output: Not Equal




In the example above as variable1 and variable2 ar referring to 2 totally different objects despite of same price .Accordingly “==” operator can come false compared each







String variable1=new String(“First”);
String variable2=variable1;



If(variable1==variable2)

else


Output: Equal

In the example above as variable1 and variable2 ar referring to 2 same objects .Accordingly “==” operator can come true compared each




3. equals () :  equals() method is used to compares the worth of 2 objects . this method is defined in Object class and can even be overridden to change the working

String variable1=new String(“First”);
String variable2=variable1;



If(variable1.equals(variable2))

else


Output: Equal


In the example above as variable1 and variable2 are referring to 2 totally different objects with same price .Accordingly equals() will come true compared each.

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How objects are stored in heap ?

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How to create custom Exception in Java

Custom Exception

Why we need custom Exception ?
How to create a custom exception ?
Write code to create a Custom Exception

All these are questions usually asked in a Java interview .So my today's post on how to create a custom exception in java .

As we know There are two types of Exception :
1. Checked Exception
2. Unchecked Exception

Both these exceptions have a common parent class Exception .So ,in same order if we have to create a custom exception ,we need to extend Exception class.

Ok , let me explain the process step by step .

1. Any custom exception should extend Exception Class .

2. There should be a proper name given to the Exception ,For example if there is an exception related to Invalid age name can be given as InvalidAgeException

public class InvalidAgeException extends Exception {}

public class InvalidAgeException extends Exception { private int age; public InvalidAgeException () { super(); } public InvalidAgeException (String message, int age) { super(message); this.age = age; }  }

In the above way we can define two constructors of InvalidAgeException with message and without message

Usage of custom Exception:

Below is the program with usage of custom exception.

public class CustomExceptionDemo  {  private static final Map<Integer, String> employee = new HashMap<>();  static  { employee.put(100, "Mahesh"); employee.put(101, "Suresh");  employee.put(102, "Bran");  employee.put(103, "Troy"); }  public static void main(String args[]) {  CustomExceptionDemo t = new CustomExceptionDemo(); t.getAge(1000); }  public String getAge(int age)  {  if (employee.get(age) == null) {  throw new InvalidAgeException ("No such employee exists", age); } return employee.get(name); } }

SO friends this was my post on Custom Exception .

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