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Ans. In GUI programming, an object that can be registered to be notified when events of some given type occur. The object is said to listener? for the events.
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Ans. A way of encoding characters as binary numbers. The Unicode character set includes characters used in many languages, not just English. Unicode is the character set that is used internally by Java.
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Ans. ThreadFactory is an interface that is meant for creating threads instead of explicitly creating threads by calling new Thread(). Its an object that creates new threads on demand. Using thread factories removes hardwiring of calls to new Thread, enabling applications to use special thread subclasses, priorities, etc.
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Ans. You can put related classes together as a single logical group.
Nested classes can access all class members of the enclosing class, which might be useful in certain cases.
Nested classes are sometimes useful for specific purposes. For example, anonymous inner classes are useful for writing simpler event-handling code with AWT/Swing.
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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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Ans. You can create a non-static local class inside a body of code. Interfaces cannot have local classes, and you cannot create local interfaces.
Local classes are accessible only from the body of the code in which the class is defined. The local classes are completely inaccessible outside the body of the code in which the class is defined.
You can extend a class or implement interfaces while defining a local class.
A local class can access all the variables available in the body of the code in which it is defined. You can pass only final variables to a local inner class.
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Q608. What will happen if class implement two interface having common method?
Ans. That would not be a problem as both are specifying the contract that implement class has to follow. If class C implement interface A & interface B then Class C thing I need to implement print() because of interface A then again Class think I need to implement print() again because of interface B, it sees that there is already a method called test() implemented so it's satisfied.
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Q609. What is the advantage of using arrays over variables ?
Ans. Arrays provide a structure wherein multiple values can be accessed using single reference and index. This helps in iterating over the values using loops.
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Q610. 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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Q614. What is an applet? What is the lifecycle of an applet?
Ans. Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser.
Lifecycle methods of Applet -
init( ) method - Can be called when an applet is first loaded start( ) method - Can be called each time an applet is started paint( ) method - Can be called when the applet is minimized or maximized stop( ) method - Can be used when the browser moves off the applet's page destroy( ) method - Can be called when the browser is finished with the applet
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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. 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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Q618. What is the difference between System.out ,System.err and System.in?
Ans. System.out and System.err both represent the monitor by default and hence can be used to send data or results to the monitor. But System.out is used to display normal messages and results whereas System.err is used to display error messages and System.in represents InputStream object, which by default represents standard input device, i.e., keyboard.
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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. throw is used to explicitly throw an exception especially custom exceptions, whereas throws is used to declare that the method can throw an exception.
We cannot throw multiple exceptions using throw statement but we can declare that a method can throw multiple exceptions using throws and comma separator.
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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. 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. IDE stands of Integrated Development Environment. Few Java IDE's are WSAD ( Websphhere Application Developer ) , RAD ( Rational Application Developer ) , Eclipse and Netbeans.
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Ans. Object is a run time entity whose state is stored in fields and behavior is shown via methods. Methods operate on an object's internal state and serve as the primary mechanism for object-to-object communication.
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Ans. A class is a blue print or Mold using which individual objects are created. A class can contain fields and methods to describe the behavior of an object.
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Which of following can be nested into another ?
