solution.txt

Q.1)   Can abstract class have constructors in Java?
Ans)   yes an abstract class have constructors in java.you can either explicity provide constructuor to abstract class or 
       if you don't compare will add default constructor of no argument in abstract class. this is true for all classes 
       and its  also applies on abstract class.


Q.2)  Can abstract class implements interface in Java? do they require to implement all methods?
Ans)  yes abstract class can implement interface by using implements keyword.they don't need to implement all methods.

Q.3)  Can abstract class be final in Java?
Ans)  no because the purpose of using both are opposite to each other.abstract class must have to get instantiated to become 
      concrete,where as final class should not get subclassed.

Q.4)  Can abstract class have static methods in Java?
Ans)  no we cannot declare a static method in abstract class.because we cannot create a instance of abstract class.

Q.5)  Can you create instance of abstract class?
Ans)  no we cannot create an instance of an abstract class because it does not have a complelte implementation.


Q.6)  Is it necessary for abstract class to have abstract method?
Ans)  yes it is necessary to declare abstract method in abstract class.


Q.7)  Difference between abstract class and interface in Java?
Ans)  Abstract Class:-
      a- abstract class is clas which conatain one or more abstract methods,which has to be implemented by its sub classes.
      b- abstract class is a class prefix with an abstract keyowrd follwed by class definition.
      c- abstract class can also contain concrete methods.
      Interface:-
      a- the classes which implement the interfaces must provide the method definition for all the methods.
      b- interface is a pure abstract class which starts with iterface keyword.
      c- interface contains all abstract method and final variable declarations.

Q.8)  When do you favor abstract class over interface?
Ans)  abstract class have both concrete and abstract function.and interface have only abstraction method.

Q.9)  What is abstract method in Java?
Ans)  Method that are declare without any body within an abstract class are called abstract method.method body will be
      defined by its subclass.

Q.10) Can abstract class contains main method in Java ?
Ans)  yes because main() method is concrete method and abstract method allow concrete method.

Q.11) what is static block in java?
Ans)  static block is used for intializing the static variables.this block gets excuted when  the class is loaded in the memory
      a class can have multiple static blocks .


Q.12) What is the need of static block?
Ans)  static block is used for initialzing variables.block gets executed when the class is loaded in the memory.

Q.13) Can we overload static methods in java?
Ans)  static method cannot be overridden because they are not dispatched on the object instance at runtime.

Q.14) Can we call super class static methods from sub class?
Ans)  If you want to call static method of a class we can call directly from another static method or by using its class
      name we can call static method of that class. 

Q.15) What is the difference between final and static keywords?
Ans)  Final keywords:-
      final keyword is applicable to class, methods and variables.it is compulsory to initialize the final variable at the
      time of its declaration.final method cannot be inherited.final keyword supports no such block.
      Static keyword:-
      Static keyword is applicable to nested static class,variaable,methods and block.it is compulsory to initialize the 
    static variable at the  time of its declaration.static members can only access the static members of the class.static block 
    is used to initialize the static variables.

Q.16) Write a note on covariant return type with example code.
Ans)  covariant return type specifies that the return type may vary in the same direction  as the subclass.
      Example:-
        class A{
	A get(){
	return this;
	}
	}
	class B extends A{
	b get()
	{return this;}
	void message()
		{
		 System.out.println("welcome");
		}
	public static void main(String args[]){
	 new b().get().message();
	}	
	}

Q.17) Write a note on Enum with example code.
Ans)  Enum is keyword for creating a Enumeration .it means a list of named constant.it define a class type.
      Example:-
      enum weekdays
      {sun,mon,tues,wed,thurs,fri,sat }
      class Test
      {
        public static void main(string args[])
	{
	  weekdays wk;
          wk=weekdays.sun;
          System.out.println("Today is"+wk);
	}
      }

Q.18) Write a note on use of super keyword and super() method.
Ans)  super keyword can be used to call immediate parent class.

Q.19) Write a code to implement abstraction using interface.
Ans)  class abc
      {
        public static void main(String args[])
        {
         twowheeler ob=new honda();
         test.run();
        }
      }

       abstract class twowheeler
       {
         public abstract void run();
       }
       class honda extends twowheeler
       {
        public void run()
        {
         System.out.println("running....");
        }
       }

Q.20) Write a Java program to sort a numeric array and a string array.
Ans)  import java.util.Arrays;
      public class abc
      { 
        public static void main (String []args)
        { 
          int [] arr={1789,2035,1899,1456,2013,1458,2458};
          String [] arr1={"java","python","php","c#","c","c++"};
          
          System.out.println("Original numeric array :"+Arrays.toString(arr));
          Arrays.sort(arr);
          System.out.println("Original numeric array :"+Arrays.toString(arr));
          
          System.out.println("Original numeric array :"+Arrays.toString(arr1));
 	  Arrays.sort(arr1);
          System.out.println("Original numeric array :"+Arrays.toString(arr1));
        }
       }
 
Q.21) Write a Java program to sum values of an array.
Ans)  import java.util.Scanner;
      class abc
      {
       public static void main(String[] args)
       {Scanner sc=new Scanner(System.in);
        int arr[]=new int arr[5];
         int sum=0;
         for(int i=0;i<5;i++)
	{
	arr[i]=sc.nextInt();	
	}
	for(int i:arr)
        sum+=i;
        System.out.println("sum"+sum);
      }
	}    

Q.22) Write a Java program to remove a specific element from an array.
Ans)  import java.util.Arrays;
      public class abc
      { 
        public static void main (String []args)
        { 
          int [] arr={25,14,52,87,15,45};
          
          System.out.println("Original numeric array :"+Arrays.toString(arr));
          int rmve=1;
          int length=arr.length;
          for(int i=rmve;i<length-1;i++){
           arr[i] =arr[i+1];
          }
         System.out.println("After removeing the sec element"+Arrays.toString(arr));
        }
       }


Q.23) Write a Java program to reverse an array of integer values.
Ans)  import java.util.Arrays;
      class abc{
       public static void main(String [] args)
	{
        int [] arr={25,14,52,87,15,45};
         int length=arr.length;
        System.out.println("Original array"+Arrays.toString(arr));
        for(int i=0;i<length/2;i++)
        {
            int temp=arr[i];
            arr[i]=arr[length-i-1];
            arr[length-i-1]=temp;
        }
       System.out.println("reverse of array"+Arrays.toString(arr));
        }
      }


Q.24) Write a Java program to find the duplicate values of an array of integer values.
Ans)   import java.util.Arrays;
      class abc{
       public static void main(String [] args)
	{
	    int [] arr={25,14,15,52,25,14,87,15,45};
	     int length=arr.length;
		for(int i=0;i<length-1;i++)
		{
		  for(int j=0;j<length;j++)
		  {
		   if((arr[i]==arr[j] && (i!=j)))	
		    { 
			System.out.println("Duplicate value"+arr[j]);		}
		    }
                  }
                }

	}}