Java Interview Questions – Part6

Q: When a thread is created and started, what is its initial state?

A: A thread is in the ready state as initial state after it has been created and started.

Q: What is the Locale class?

A: The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.

Q: What are synchronized methods and synchronized statements?

A: Synchronized methods are methods that are used to control access to an object. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement.

Q: What is runtime polymorphism or dynamic method dispatch?

A: Runtime polymorphism or dynamic method dispatch is a process in which a call to an overridden method is resolved at runtime rather than at compile-time. In this process, an overridden method is called through the reference variable of a superclass.

Q: What is Dynamic Binding(late binding)?

A: Binding refers to the linking of a procedure call to the code to be executed in response to the call. Dynamic binding means that the code associated with a given procedure call is not known until the time of the call at run-time.

Q: Can constructor be inherited?

A: No, constructor cannot be inherited.

Q: What are the advantages of ArrayList over arrays?

A: ArrayList can grow dynamically and provides more powerful insertion and search mechanisms than arrays.

Q: Why deletion in LinkedList is fast than ArrayList?

A: Deletion in linked list is fast because it involves only updating the next pointer in the node before the deleted node and updating the previous pointer in the node after the deleted node.

Q: How do you decide when to use ArrayList and LinkedList?

A: If you need to frequently add and remove elements from the middle of the list and only access the list elements sequentially, then LinkedList should be used. If you need to support random access, without inserting or removing elements from any place other than the end, then ArrayList should be used.

Q: What is a Values Collection View ?

A: It is a collection returned by the values() method of the Map Interface, It contains all the objects present as values in the map.

Q: What is dot operator?

A: The dot operator(.) is used to access the instance variables and methods of class objects.It is also used to access classes and sub-packages from a package.

Q: Where and how can you use a private constructor?

A: Private constructor is used if you do not want other classes to instantiate the object and to prevent subclassing.T

Q: What is type casting?

A: Type casting means treating a variable of one type as though it is another type.

Q: Describe life cycle of thread?

A: A thread is a execution in a program. The life cycle of a thread include:

• Newborn state
• Runnable state
• Running state
• Blocked state
• Dead state

Q: What is the difference between the >> and >>> operators?

A: The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

Q: Which method of the Component class is used to set the position and size of a component?

A: setBounds() method is used for this purpose.

Q: What is the range of the short type?

A: The range of the short type is -(2^15) to 2^15 – 1.

Q: What is the immediate superclass of Menu?

A: MenuItem class

Q: Does Java allow Default Arguments?

A: No, Java does not allow Default Arguments.

Q: Which number is denoted by leading zero in java?

A: Octal Numbers are denoted by leading zero in java, example: 06

Q: Which number is denoted by leading 0x or 0X in java?

A: Hexadecimal Numbers are denoted by leading 0x or 0X in java, example: 0XF

Q: Break statement can be used as labels in Java?

A: Yes, an example can be break one;

Q: Where import statement is used in a Java program?

A: Import statement is allowed at the beginning of the program file after package statement.

Q: Explain suspend() method under Thread class>

A: It is used to pause or temporarily stop the execution of the thread.

Q: Explain isAlive() method under Thread class?

A: It is used to find out whether a thread is still running or not.

Q: What is currentThread()?

A: It is a public static method used to obtain a reference to the current thread.

Q: Explain main thread under Thread class execution?

A: The main thread is created automatically and it begins to execute immediately when a program starts. It ia thread from which all other child threads originate.

Q: Life cycle of an applet includes which steps?

A: Life cycle involves the following steps:

• Initialization
• Starting
• Stopping
• Destroying
• Painting

Q: Why is the role of init() method under applets?

A: It initializes the applet and is the first method to be called.

Q: Which method is called by Applet class to load an image?

A: getImage(URL object, filename) is used for this purpose.

Q: Define code as an attribute of Applet?

A: It is used to specify the name of the applet class.

Q: Define canvas?

A: It is a simple drawing surface which are used for painting images or to perform other graphical operations.

Q: Define Network Programming?

A: It refers to writing programs that execute across multiple devices (computers), in which the devices are all connected to each other using a network.

Q: What is a Socket?

A: Sockets provide the communication mechanism between two computers using TCP. A client program creates a socket on its end of the communication and attempts to connect that socket to a server.

Q: Advantages of Java Sockets?

A: Sockets are flexible and sufficient. Efficient socket based programming can be easily implemented for general communications. It cause low network traffic.

Q: Disadvantages of Java Sockets?

A: Socket based communications allows only to send packets of raw data between applications. Both the client-side and server-side have to provide mechanisms to make the data useful in any way.

Q: Which class is used by server applications to obtain a port and listen for client requests?

A: java.net.ServerSocket class is used by server applications to obtain a port and listen for client requests

Q: Which class represents the socket that both the client and server use to communicate with each other?

A: java.net.Socket class represents the socket that both the client and server use to communicate with each other.

Q: Why Generics are used in Java?

A: Generics provide compile-time type safety that allows programmers to catch invalid types at compile time. Java Generic methods and generic classes enable programmers to specify, with a single method declaration, a set of related methods or, with a single class declaration, a set of related types.

Q: What environment variables do I need to set on my machine in order to be able to run Java programs?

A: CLASSPATH and PATH are the two variables.

Q: Is there any need to import java.lang package?

A: No, there is no need to import this package. It is by default loaded internally by the JVM.

Q: What is Nested top-level class?

A: If a class is declared within a class and specify the static modifier, the compiler treats the class just like any other top-level class. Nested top-level class is an Inner class.

Q: What is Externalizable interface?

A: Externalizable is an interface which contains two methods readExternal and writeExternal. These methods give you a control over the serialization mechanism.

Q: If System.exit (0); is written at the end of the try block, will the finally block still execute?

A: No in this case the finally block will not execute because when you say System.exit (0); the control immediately goes out of the program, and thus finally never executes.