• No. We can not create constructor with static.
• If we try to create a static constructor compile time error will come: Illegal modifier for the constructor

• Constructors will be used to assign instance variables with default values.
• Whenever object is created constructor will be called so the default values for the instance variables will be assigned in this constructor.
• Top 15 Java Interview Questions on Constructors

• Static keyword is mainly used for memory management.
• Static variables get memory when class loading itself.
• Static variables can be used to point common property all objects.

• Static means class level.
• Constructor will be use to assign initial values for instance variables
• static and constructor are different and opposite from each other.
• To assign initial values for instance variable we use constructor.
• To assign static variables we use Static Blocks
• We can use static blocks to initialize static variables in java.

• Class loading time itself these variables gets memory
• Static methods are the methods with static keyword are class level. without creating the object of the class we can call these static methods.


1. public static void show(){ 
2.  
3. }


• Static block also known as static initializer
• Static blocks are the blocks with static keyword.
• Static blocks wont have any name in its prototype.
• Static blocks are class level.
• Static block will be executed only once.
• No return statements.
• No arguments.
• No this or super keywords supported.
 

1. static{ 
2.  
3.  }

  1.Static Variables 

  2.Static Methods 

  3.Static Blocks

  4.Main method

• Hi friends now we are going to check our pc is having internet connection or not using java code 
• yes we can check internet connection using java code java.net package providing some useful classes.
• Using java.net.URL and java.net.URLConnection classes we need to check we can check we have a connection or not.
• Lets see the program to detect internet connection using java

• By using  getRuntime() method of java.lang.Runtime  we can also test internet connection in java
• The output will be 0 if internet connection available 1 if not.

• No. Return type must be same in super class and sub class.

• Compile time error will come.
  

1. package MethodOverridingExamplePrograms;
2. public class Super{
3.  
4. public void add(){
5.  System.out.println("Super class add method");
6. }
7. 
   
8. }

1. package MethodOverridingInterviewPrograms;
2. public class Sub extends Super{
3.   
4. void add(){ //Compiler Error: Cannot reduce the visibility of the inherited method
5. from Super
6.  
7. System.out.println("Sub class add method");
8. 
   
9. }
10. 
    
11. }

7.Can we override a super class method without throws clause to with throws clause in the sub class?

• Yes if super class method throws unchecked exceptions.
• No need if super class method throws checked exceptions. But it is recommended to add in sub class method in order to maintain exception messages.

 8.What are the rules we need to follow in overriding if super class method throws exception ?

•  Exception handling in method overriding

 9.What happens if we not follow these rules if super class method throws some exception.

•  Compile time error will come.

1. package MethodOverridingExamplePrograms;
2. public class Super{
3.  
4. public void add(){
5.  System.out.println("Super class add method");
6. }
7. 
   
8. }

1. package MethodOverridingInterviewPrograms;
2. public class Sub extends Super{
3.   
4. void add() throws Exception{ //Compiler Error: Exception Exception is not compatible with
5. throws clause in Super.add()
7. System.out.println("Sub class add method");
8. 
   
9. }
10. 
    
11. }

1. package MethodOverridingExamplePrograms;
2. public class Super{
3.  
4. public void add(){
5.  System.out.println("Super class add method");
6. }
7. 
   
8. }

1. package MethodOverridingInterviewPrograms;
2. public class Sub extends Super{
3.   
4. void add() throws NullPointerException{ // this method throws unchecked exception so no
5. isuues
7. System.out.println("Sub class add method");
8. 
   
9. }
10. 
    
11. }

10.Can we change an exception of a method with throws clause from unchecked to checked while overriding it?

•  No. As mentioned above already
• If super class method throws exceptions in sub class if you want to mention throws  then use  same class  or its  sub class exception.
• So we can not change from unchecked to checked 

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 Method overloading interview questions java

• Hiding the implementation  and showing the function definition to the user.
• Abstract class contains abstract methods and concrete methods(normal methods)

• Using abstract keyword we can define abstract class.
• Check below code for abstract class example program. 

3. How to declare an abstract method?

• By Using abstract keyword in the method signature we can declare abstract method.

 4. Can we define abstract class without abstract method?

•  Yes we can define abstract class without abstract methods.
• It is not mandatory to create at-least one abstract method in abstract class.

• Abstract class can not be instantiated directly.
• Means we can not create object for abstract class directly.
• Through sub class abstract class members will get memory. Whenever we create sub class object of abstract class  abstract class object will be created. i.e abstract class members will get memory at that time.

• No. its not possible to declare abstract method with static keyword.
• If we declare abstract method with static compiler will throw an error.

• No. its not possible to declare abstract method with final keyword.
• If we declare abstract method with final compiler will throw an error.
• Because abstract methods should be override by its sub classes.

• No. its not possible to declare abstract method with private .
• If we declare abstract method with private compiler will throw an error.
• Because abstract methods should be override by its sub classes.

• Yes we can declare abstract methods as public.

• Yes we can declare abstract methods with default.

• Yes we can declare abstract methods as protected.

• public,  protected and default are valid.
• static,  final and private are invalid.

• Yes. We can define an abstract class with throws clause.

• If sub class which is extending abstract class not overriding abstract method compiler will throw an error.

• Yes we can escape from overriding abstract method from super abstract class by making our class again as abstract.
• The class which is extending our class will get responsibility of overriding all abstract methods in our class and in super class.

• 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.
• let us see a program on how to call a static method of a class

• We can also call static method like this but this is not recommended.

• Now our question is can we call super class static method from sub class?
• Yes we can call super class static method inside sub class using super_class_method();
• We can also call super class static method using Sub_class_name.superclass_staticMethod()

• If the same static method defined in sub class also then we can not call super class method using sub class name if we call them sub class static method will be executed.

1. Can we Overload static methods in java
2. Can we Override static methods in java

1. what is the output of following program:

2. what is the output of following program:

3. what is the output of following program:

4. what is the output of following program: