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Q1951. Difference between Factory and Strategy Design Pattern ?

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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Q1952. 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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Q1953. Which kind of memory is used for storing object member variables and function local variables ?

Ans. Local variables are stored in stack whereas object variables are stored in heap.

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Q1954. Why do member variables have default values whereas local variables don't have any default value ?

Core Java

Ans. member variable are loaded into heap, so they are initialized with default values when an instance of a class is created. In case of local variables, they are stored in stack until they are being used.

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Q1955. What is a Default Constructor ?

Core Java

Ans. The no argument constructor provided by Java Compiler if no constructor is specified.

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Q1956. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?

Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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Q1957. Can we overload constructors ?

Ans. Yes.

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Q1958. 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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Q1959. 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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Q1960. 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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Q1961. 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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Q1962. 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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Q1963. Can finally block be used without catch ?

Core Java

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

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Q1964. What is exception propogation ?

Core Java

Ans. Passing the exception object to the calling method.

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Q1965. 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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Q1966. What is a nested interface ?

Ans. Any interface declared inside a class or an interface. It is static by default.

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Q1967. 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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Q1968. Difference between serializable and externalizable interface ?

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

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Q1969. 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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Q1970. 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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Q1971. Can we declare an abstract method private ?

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

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Q1972. 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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Q1973. What is a config Object?

Java EE

Ans. The config object is an instantiation of javax.servlet.ServletConfig and is a direct wrapper around the ServletConfig object for the generated servlet. This object allows the JSP programmer access to the Servlet or JSP engine initialization parameters such as the paths or file location.

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Q1974. What is a pageContext Object?

Java EE

Ans. The pageContext object is an instance of a javax.servlet.jsp.PageContext object. The pageContext object is used to represent the entire JSP page. This object stores references to the request and response objects for each request. The application, config, session, and out objects are derived by accessing attributes of this object.The pageContext object also contains information about the directives issued to the JSP page, including the buffering information, the errorPageURL, and page scope.

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Q1975. What is suspend() method used for ?

Ans. suspend() method is used to suspend the execution of a thread for a period of time. We can then restart the thread by using resume() method.

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Q1976. Difference between suspend() and stop() ?

Ans. Suspend method is used to suspend thread which can be restarted by using resume() method. stop() is used to stop the thread, it cannot be restarted again.

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Q1977. What are the benefits of using Spring Framework ?

Spring

Ans. Spring enables developers to develop enterprise-class applications using POJOs. The benefit of using only POJOs is that you do not need an EJB container product.

Spring is organized in a modular fashion. Even though the number of packages and classes are substantial, you have to worry only about ones you need and ignore the rest.

Spring does not reinvent the wheel instead, it truly makes use of some of the existing technologies like several ORM frameworks, logging frameworks, JEE, Quartz and JDK timers, other view technologies.

Testing an application written with Spring is simple because environment-dependent code is moved into this framework. Furthermore, by using JavaBean-style POJOs, it becomes easier to use dependency injection for injecting test data.

Spring is web framework is a well-designed web MVC framework, which provides a great alternative to web frameworks such as Struts or other over engineered or less popular web frameworks.

Spring provides a convenient API to translate technology-specific exceptions (thrown by JDBC, Hibernate, or JDO, for example) into consistent, unchecked exceptions.

Lightweight IoC containers tend to be lightweight, especially when compared to EJB containers, for example. This is beneficial for developing and deploying applications on computers with limited memory and CPU resources.

Spring provides a consistent transaction management interface that can scale down to a local transaction

Sample Code for spring

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Q1978. what is the difference between collections class vs collections interface ?

Core Java

Ans. Collections class is a utility class having static methods for doing operations on objects of classes which implement the Collection interface. For example, Collections has methods for finding the max element in a Collection.

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Q1979. Will this code give error if i try to add two heterogeneous elements in the arraylist. ? and Why ?

List list1 = new ArrayList<>();
list1.add(5);
list1.add("5");

Ans. If we don't declare the list to be of specific type, it treats it as list of objects.

int 1 is auto boxed to Integer and "1" is String and hence both are objects.

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Q1980. What is the difference between System.console.write and System.out.println ?

Ans. System.console() returns null if your application is not run in a terminal (though you can handle this in your application)System.console() provides methods for reading password without echoing charactersSystem.out and System.err use the default platform encoding, while the Console class output methods use the console encoding

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