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Q781. Different types of memory used by JVM ?

Core Java

Ans. Class , Heap , Stack , Register , Native Method Stack.

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Q782. Can we declare interface methods as private ?

Ans. With Java 9 we can declare interface methods as private

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Q783. What is a Static import ?

Core Java

Ans. By static import , we can access the static members of a class directly without prefixing it with the class name.

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Very frequently asked. Usually difference between String,StringBuffer and StringBuilder is asked in different variations.

Q784. Difference between StringBuffer and StringBuilder ?

Core Java

Ans. StringBuffer is synchronized whereas StringBuilder is not.

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Q785. What is a Property class ?

Core Java

Ans. The properties class is a subclass of Hashtable that can be read from or written to a stream.

Sample Code for Load Properties using Property Class

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Very frequently asked in different variations. Frequently asked in Deloitte ( 2 feedback ) , HCL Tech ( 3 feedback ), TCS and Coginizant (CTS)

Q786. Explain the scenerios to choose between String , StringBuilder and StringBuffer ?

or

What is the difference between String , StringBuilder and StringBuffer ?

Core Java

Ans. If the Object value will not change, use String Class because a String object is immutable.

If the Object value can change and will only be modified from a single thread, use StringBuilder because StringBuilder is unsynchronized(means faster).

If the Object value may change, and can be modified by multiple threads, use a StringBuffer because StringBuffer is thread safe(synchronized).

Sample Code for String

Sample Code for StringBuffer

Sample Code for StringBuilder

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Q787. Can we have multiple servlets in a web application and How can we do that ?

Java EE

Ans. Yes by making entries in web.xml

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Q788. How can we manage Error Messages in the web application ?

Solution

Ans. Within message.properties file.

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Q789. Difference between Factory and Abstract Factory Design Pattern ?

Design

Ans. Factory Pattern deals with creation of objects delegated to a separate factory class whereas Abstract Factory patterns works around a super-factory which creates other factories.

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Q790. Difference between Factory and Builder Design Pattern ?

Design

Ans. Builder pattern is the extension of Factory pattern wherein the Builder class builds a complex object in multiple steps.

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Q791. Difference between Proxy and Adapter ?

Design

Ans. Adapter object has a different input than the real subject whereas Proxy object has the same input as the real subject. Proxy object is such that it should be placed as it is in place of the real subject.

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Q792. Difference between Adapter and Facade ?

Design

Ans. The Difference between these patterns in only the intent. Adapter is used because the objects in current form cannot communicate where as in Facade , though the objects can communicate , A Facade object is placed between the client and subject to simplify the interface.

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Q793. Difference between Builder and Composite ?

Ans. Builder is a creational Design Pattern whereas Composite is a structural design pattern. Composite creates Parent - Child relations between your objects while Builder is used to create group of objects of predefined types.

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Q794. Example of Chain of Responsibility Design Pattern ?

Ans. Exception Handling Throw mechanism.

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Q795. Example of Observer Design Pattern ?

Ans. Listeners.

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Q796. Difference between Factory and Strategy Design Pattern ?

Design

Ans. Factory is a creational design pattern whereas Strategy is behavioral design pattern. Factory revolves around the creation of object at runtime whereas Strategy or Policy revolves around the decision at runtime.

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Q797. Shall we use abstract classes or Interfaces in Policy / Strategy Design Pattern ?

Ans. Strategy deals only with decision making at runtime so Interfaces should be used.

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Q798. What will happen if we make the constructor private ?

Core Java

Ans. We can't create the objects directly by invoking new operator.

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Q799. How can we create objects if we make the constructor private ?

Core Java

Ans. We can do so through a static public member method or static block.

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Q800. Why Java don't use pointers ?

Ans. Pointers are vulnerable and slight carelessness in their use may result in memory problems and hence Java intrinsically manage their use.

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Q801. Can we use both "this()" and "super()" in a constructor ?

Core Java

Ans. No, because both this and super should be the first statement.

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Q802. Is it necessary that each try block to be followed by catch block ?

Core Java

Ans. It should be followed by either catch or finally block.

Sample Code for Retry in case of exception

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Q803. Can finally block be used without catch ?

Core Java

Ans. Yes but should follow "try" block then.

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Q804. Difference between nested and inner classes ?

Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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Q805. What is an Externalizable interface ?

Ans. Externalizable interface is used to write the state of an object into a byte stream in compressed format.

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Q806. Difference between serializable and externalizable interface ?

Ans. Serializable is a marker interface whereas externalizable is not.

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Q807. What is reflection ?

Ans. It is the process of examining / modifying the behaviour of an object at runtime.

Sample Code for reflection

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Q808. Can we instantiate the object of derived class if parent constructor is protected ?

Core Java

Ans. Yes, as protected constructor is accessible in sub class.

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Q809. Can we declare an abstract method private ?

Ans. No Abstract methods can only be declared protected or public.

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Q810. What are the design considerations while making a choice between using interface and abstract class ?

Core Java

Ans. Keep it as a Abstract Class if its a "Is a" Relationsship and should do subset/all of the functionality. Keep it as Interface if its a "Should Do" relationship.

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