JAVA Interview FAQ.

prasannavigneshr · #1 (**permalink**) 09-10-2007, 11:00 PM

Hi Techies,

Let's start posting JAVA interview questions and answers in this thread.

Thanks

prasannavigneshr · #2 (**permalink**) 09-10-2007, 11:00 PM

What are different types of inner classes?

Nested top-level classes, Member classes, Local classes, Anonymous classes
Nested top-level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other top-level class.
Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, […]

prasannavigneshr · #3 (**permalink**) 09-10-2007, 11:01 PM

What are Checked and UnChecked Exception?

A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream’s read() method
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also […]

prasannavigneshr · #4 (**permalink**) 09-10-2007, 11:02 PM

Can I import same package/class twice? Will the JVM load the package twice at runtime?

One can import the same package or same class multiple times. Neither compiler nor JVM complains abt it. And the JVM will internally load the class only once no matter how many times you import the same class.

prasannavigneshr · #5 (**permalink**) 09-10-2007, 11:04 PM

Can I have multiple main methods in the same class?

No the program fails to compile. The compiler says that the main method is already defined in the class.

prasannavigneshr · #6 (**permalink**) 09-10-2007, 11:07 PM

Can an application have multiple classes having main method?

Yes it is possible. While starting the application we mention the class name to be run. The JVM will look for the Main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.

prasannavigneshr · #7 (**permalink**) 09-10-2007, 11:15 PM

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

CLASSPATH and PATH are the two variables.

prasannavigneshr · #8 (**permalink**) 09-10-2007, 11:15 PM

How can one prove that the array is not null but empty?

Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.

prasannavigneshr · #9 (**permalink**) 09-10-2007, 11:16 PM

What is the first argument of the String array in main method?

The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.

prasannavigneshr · #10 (**permalink**) 09-10-2007, 11:17 PM

What if I do not provide the String array as the argument to the method?

Program compiles but throws a runtime error “NoSuchMethodError”.

prasannavigneshr · #11 (**permalink**) 09-10-2007, 11:18 PM

What if I write static public void instead of public static void?

Program compiles and runs properly.

prasannavigneshr · #12 (**permalink**) 09-10-2007, 11:19 PM

What if the static modifier is removed from the signature of the main method?

The program compiles properly but at runtime it will give “Main method not public.” message.

prasannavigneshr · #13 (**permalink**) 09-10-2007, 11:19 PM

What is a compilation unit?

A compilation unit is a Java source code file.

prasannavigneshr · #14 (**permalink**) 09-10-2007, 11:20 PM

What is the purpose of garbage collection?

The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and reused.

prasannavigneshr · #15 (**permalink**) 09-10-2007, 11:20 PM

How are this and super used?

this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.

prasannavigneshr · #16 (**permalink**) 09-10-2007, 11:21 PM

What interface must an object implement before it can be written to a stream as an object?

An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.

prasannavigneshr · #17 (**permalink**) 09-10-2007, 11:22 PM

Which package is always imported by default?

The java.lang package is always imported by default.

prasannavigneshr · #18 (**permalink**) 09-10-2007, 11:22 PM

What is your platform’s default character encoding?

If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1

prasannavigneshr · #19 (**permalink**) 09-10-2007, 11:23 PM

What happens when you add a double value to a String?

The result is a String object.162.

prasannavigneshr · #20 (**permalink**) 09-10-2007, 11:24 PM

What is the difference between the File and RandomAccessFile classes?

The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.

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