java interview questions for experienced

Why we preferred event-delegation model over earlier event-inheritance model?

The event-delegation model has two advantages over the event-inheritance model.

• Event-delegation helps in event handling by objects other than those who generate the events.
• Help in differentiating between component design and its use.
• Event-delegation performs much better in applications where generation of events takes place.
• Event-delegation model does not repeatedly process unhandled events, which cause improvement in the performance.

How is Java source code files named?

Java source code file takes the name of a public class or interface that is defined by the programmer while coding within the file. Source code file may contain maximum one public class or interface in the file. Two cases me occur while naming of the java source code file:

• When public class or interface is defined within a source code file then the java source code file must take the name of the public class or interface defined while coding.
• When no public class or interface is defined inside a source code file, then the java source code file take a name that is different than its classes and interfaces. Source code files use the .java extension.

What are the advantages of Java layout managers?

In Java Button, Checkbox, Lists, Scrollbars, Text Fields, and Text Area etc positioned by the default layout manager. Using algorithm layout manager automatically arranges the controls within a window. In Windows environment, we can control layout manually. But we do not do it manual because of following two reasons:

• It is very tedious to manually lay out a large number of components.
• Sometimes the width and height information is not available when you need to arrange some control, because the native toolkit components have not been realized. This is a chicken-and-egg situation.

Java uses layout managers to lay out components in a consistent manner across all windowing platforms.

What is the difference between a Choice and a List?

The between Choice and list are following:

• Choice class presents a pop-up menu of choices whereas List is a collection of different visible item.
• Choice is displayed in a compact form, to see the list of available choices we need to scroll down whereas list displays the entire available items.
• Choice allows selecting only one items but List supports the selection of one or more List items.
• Lists typically allow duplicate elements selection. List allow pairs of elements e1 and e2 such that e1.equals(e2), and they typically allow multiple null elements if they allow null elements at all.

What is the difference between the event model and the event-delegation model?

Difference between event model and event-delegation are following:

• The event-delegation model eliminates the processing required to support in the handling of unhandled events.
• Event delegation model allow components to handle their own events. When components are unable to handle a particular event, then event is inherited by the component container.
• In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces.
• The JDK 1.02 event model uses an event inheritance

What restrictions are placed on method overriding?

The restrictions on method overloading are the signature of the method.

• Signature is number, type, and order of the arguments passed to a method.
• Overridden methods must have the same name, argument list, and return type.
• Any method which has the same name cannot have the same signature.
• They can have the same return types in the same scope.
• The compiler uses the signature to detect which overloaded method to refer when an overloaded method is called.
• If two methods have the same name and signature the compiler will throw a runtime error.

What is numeric promotion?

Numeric promotions are used for the conversion of the operands of a numeric operator into a common type. This conversation is performed so that we can easily perform the calculation on it.

• It is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations can be performed over it.
• In this byte, char, and short values are converted to int values.
• The int values are also converted to long values. The long and float values are converted to double values.

Can you compare SWING and AWT?

Swing components operate same as AWT components, the only differences are that Swing provides a number of new event types.

• Few Swing components don't have an AWT counterpart.
• Swing is an extension of AWT. It is not the replacement for the AWT.
• The advantages of Swing components is components are not rendered on the screen by the operating system, the look and feel of a component does not change when application is running on different platform using different versions.
• It is possible to cause Swing components to mimic the look and feel of a specific platform no matter what platform the program is running on. This is known as pluggable look and feel.

Does networking is support in Java ?

Yes, Java supports two types of classes:

• Low-Level Classes: provide support for socket programming like Socket, DatagramSocket, and ServerSocket classes.
• High-Level Classes: provide web programming URL, URLEncoder, and URLConnection classes.

Networking programming classes ease the programming of network applications. Java networking like anything else in Java is platform-independent.

Describe java's security model.

The Java security model was introduced in Java 2. It is divided into two pieces:

• User Adjustable Security Manager: checks various API operations like file access
• Byte Code Verifier: that asserts the validity of compiled byte code.

Public abstract class SecurityManager java.lang. SecurityManager is an abstract class which helps to different applications subclass to implement a particular security policy. It allows an application to determine whether or not a particular operation will generate a security exception.

What is Race condition?

Race Condition: It is the situation when two threads raise the request for the same resource allocation, but the manner in which resources are allocated are significant, is called race conditions.

• Race condition is created in program in order to run the parallel execution of program by using multiple threads in a same period.
• A race condition occurs when two threads operate on same object without proper synchronization and there operation interleaves on each other.
• The risk of Race condition is higher in Java.

What is difference between StringBuffer and StringBuilder in Java?

The difference between StringBuffer and StringBuilder are following:

• StringBuffer is uses mutable String, all public methods are synchronized which makes it thread-safe but same time slow but In JDK 5 they provided StringBuilder which is copy of StringBuffer without synchronization.
• StringBuilder is compatible with StringBuffer, but synchronization property is may not compatible.
• StringBuilder is a little faster than StringBuffer.

What is Marker Interface?

Marker interface in Java is interfaces with no field or methods. Uses of Mark Interfaces are following:

• We use Marker interface to tell java complier to add special behavior to the class implementing it.
• Java marker interface has no members in it.
• It is implemented by classes in get some functionality.

Example: when we want to save the state of an object then we implement serializable interface.

What is the main difference between shallow cloning and deep cloning of objects?

The differences between shallow cloning and deep cloning are:

• Java supports shallow cloning of objects by default when a class implements the java.lang.Cloneable interface where as Deep cloning is faster to develop and easier to maintain but carries a performance overhead.
• A shallow is a copy of the collection structure whereas Deep cloning copies duplicate everything.
• In Shallow copy, individual elements can be shared between two collection but in case of deep cloning two collections with all of the elements is the original collection duplicate.

What are the difference between throw and throws?

The differences are between throw and throws are:

• Throw is used to trigger an exception where as throws is used in declaration of exception.
• Without throws, Checked exception cannot be handled where as checked exception can be propagated with throws.
• Throw is used inside the method where as throws is used with the method signature.
• Throw is followed by an instance but throws is followed by class.

What is difference between preemptive scheduling and time slicing?

Differences between preemptive and time scheduling are:

• In Preemptive scheduling the highest priority task executes until it enters the waiting or dead stated or a higher priority task comes into existence.
• Time slicing, a task executes for a predefined time period and then the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factor.

What differences are between submit and execute method with ThreadPoolExecutor?

The difference between submit and execute method with ThreadPoolExecutor are:

• When our tasks throw an exception and if it was submitted with execute this exception will go to the uncaught exception handler. If you submitted the task with submit any thrown exception, checked or not, is then part of the task return status.

What is the difference between final, finally and finalize methods in Java?

Final – a key word to define constants.

• After declaring a class as final we cannot divide it into subclasses.
• When a method is marked final, it cannot be overridden by the subclass.
• When a field is marked final, its value once set, cannot be reset.

Finally – The finally block is always used with try and catch blocks, except that, when try block uses System.exit(0) call.

• It is ensured for unexpected error, the finally block do the execution which is mention in last clause of a try catch block.
• It is a block of statements that is executed irrespective if or if not an exception was caught in the preceding try block.

Finalize() – This method is linked with garbage collection.

• This method is invoked automatically, just before the collection of garbage value.

What are the types of casting?

There are two types of casting:

• Casting between primitive numeric types, and
• Casting between object references.

Casting between numeric types is used to convert larger values, like double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.

Describe what happens when an object is created in Java.

Several things happen in a particular order to ensure the object is constructed properly:

1. Memory allocation: To hold all instance variables and implementation-specific data of the object and its super classes.
2. Initialization: the objects are initialized to their default values.
3. Constructor: Constructors call the constructors for its super classes. This process continues until the constructor for java.lang.Object is called, as java.lang.Object is the base class for all objects in java.
4. Execution: Before the body of the constructor is executed all instance variable initializes and initialization blocks must get executed. Then the body of the constructor is executed.