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Ans. The memory pool containing all the reflective data of the java virtual machine itself, such as class and method objects. With Java VMs that use class data sharing, this generation is divided into read-only and read-write areas. The Permanent generation contains metadata required by the JVM to describe the classes and methods used in the application. The permanent generation is populated by the JVM at runtime based on classes in use by the application. In addition, Java SE library classes and methods may be stored here.
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Ans. The Permanent Generation (PermGen) space has completely been removed and is kind of replaced by a new space called Metaspace. The consequences of the PermGen removal is that obviously the PermSize and MaxPermSize JVM arguments are ignored and you will never get a java.lang.OutOfMemoryError: PermGen error.
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Ans. The accessibility (public, protected, etc.) of the static nested class is defined by the outer class.
A static nested class is not an inner class, it's a top-level nested class.
The name of the static nested class is expressed with OuterClassName.NestedClassName syntax.
When you define an inner nested class (or interface) inside an interface, the nested class is declared implicitly public and static.
Static nested classes can be declared abstract or final.
Static nested classes can extend another class or it can be used as a base class.
Static nested classes can have static members.
Static nested classes can access the members of the outer class (only static members, obviously).
The outer class can also access the members (even private members) of the nested class through an object of nested class. If you don't declare an instance of the nested class, the outer class cannot access nested class elements directly.
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Ans. The accessibility (public, protected, etc.) of the inner class is defined by the outer class.
Just like top-level classes, an inner class can extend a class or can implement interfaces.
Similarly, an inner class can be extended by other classes, and an inner interface can be implemented or extended by other classes or interfaces.
An inner class can be declared final or abstract.Inner classes can have inner classes, but you will have a hard time reading or understanding such complex nesting of classes.
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Which of the following is not type of inner classes ?
Simple Inner Class
Static Nested Inner Class
Method Nested Static Inner Class
Anonymous Inner Class
Which of following can be nested into another ?
class within another class
class within interface
interface within class
All of above
Q845. Difference between Class#getInstance() and new operator ?
Ans. Class.getInstance doesn't call the constructor whereas if we create an object using new operator , we need to have a matching constructor or copiler should provide a default constructor.
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Ans. Cloneable is a declaration that the class implementing it allows cloning or bitwise copy of it's object state. It is not having any method because it is a MARKER interface.
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Ans. Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are:
User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password
Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server
URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change.
Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser.
HttpSession- places a limit on the number of sessions that can exist in memory.
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Ans. It's a technique to allow multiple clients to make use of a cached set of shared and reusable connection objects providing access to a database or other resource.
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Ans. Collections are re-sizable in nature. We can increase or decrease the size as per recruitment.
Collections can hold both homogeneous and heterogeneous data's.
Every collection follows some standard data structures.
Collection provides many useful built in methods for traversing,sorting and search.
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Ans. Both bitwise right shift operator ( >> ) and bitwise zero fill right shift operator ( >>> ) are used to shift the bits towards right. The difference is that >> will protect the sign bit whereas the >>> operator will not protect the sign bit. It always fills 0 in the sign bit.
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Ans. Generalization or UpCasting is a phenomenon where a sub class is prompted to a super class, and hence becomes more general. Generalization needs widening or up-casting. Specialization or DownCasting is a phenomenon where a super class is narrowed down to a sub class. Specialization needs narrowing or down-casting.
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Ans. Yes, We can call garbage collector directly but it doesn't guarantees that the gc will start executing immediately. This gc( ) method appears in both Runtime and System classes of java.lang package.
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Ans. Volatile is an instruction that the variables can be accessed by multiple threads and hence shouldn't be cached. As volatile variables are never cached and hence their retrieval cannot be optimized.
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Ans. Java is a portable-language because without any modification we can use Java byte-code in any platform(which supports Java). So this byte-code is portable and we can use in any other major platforms.
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Ans. No. Every Class only needs to have one constructor - With parameters or without parameters. Compiler provides a default non parameterized constructor if no constructors is defined.
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Ans. No. Even though "this" would mean a reference to current object id the method gets called using object reference but "this" would mean an ambiguity if the same static method gets called using Class name.
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Ans. Both belong to the class as a whole and not to the individual objects. Static methods are explicitly called for execution whereas Static block gets executed when the Class gets loaded by the JVM.
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Ans. Java runs on a variety of platforms, such as Windows, Mac OS, and the various versions of UNIX/Linux like HP-Unix, Sun Solaris, Redhat Linux, Ubuntu, CentOS, etc
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Ans. It is used to sort collections and arrays of objects using the collections.sort() and java.utils. The objects of the class implementing the Comparable interface can be ordered.
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Ans. Break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.
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Q869. Variable of the boolean type is automatically initialized as?
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Which of the following is not type of inner classes ?
