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|What is the difference between an Interface and an Abstract class?|
An abstract class can have instance methods that implement a default behavior. An abstract class is a class which may have the usual flavors of class members (private, protected, etc.), but has some abstract methods.
An Interface can only declare constants and instance methods, but cannot implement default behavior and all methods are implicitly abstract. An interface has all public members and no implementation.
|What is the purpose of garbage collection in Java, and when is it used?|
The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used.
|Explain different way of using thread?|
|The thread could be implemented by using runnable interface or by inheriting from the Thread class. The former is more advantageous, 'cause when you are going for multiple inheritance..the only interface can help.|
|What are pass by reference and pass by value?|
|Pass By Reference means the passing the address itself rather than passing the value. Passby Value means passing a copy of the value to be passed.|
|What is HashMap and Map?|
|Map is Interface and Hashmap is class that implements that.|
|Difference between HashMap and HashTable?|
The HashMap class is roughly equivalent to Hashtable.
HashMap is unsynchronized and Hashtable is synchronized and HashMap allows null values as key and value whereas Hashtable does't allow.
HashMap does not guarantee that the order of the map will remain constant over time.
|Difference between Vector and ArrayList?|
|Vector is synchronized whereas arraylist is not.|
|Difference between Swing and Awt?|
|AWT are heavy-weight componenets. Swings are light-weight components. Hence swing works faster than AWT.|
|What is the difference between a constructor and a method?|
A constructor is a member function of a class that is used to create objects of that class. It has the same name as the class itself, has no return type, and is invoked using the new operator.
A method is an ordinary member function of a class. It has its own name, a return type (which may be void), and is invoked using the dot operator.
|What is an Iterator?|
|Some of the collection classes provide traversal of their contents via a java.util.Iterator interface. This interface allows you to walk through a collection of objects, operating on each object in turn. Remember when using Iterators that they contain a snapshot of the collection at the time the Iterator was obtained; generally it is not advisable to modify the collection itself while traversing an Iterator. State the significance of public, private, protected, default modifiers both singly and in combination and state the effect of package relationships on declared items qualified by these modifiers? public : Public class is visible in other packages, field is visible everywhere (class must be public too) private : Private variables or methods may be used only by an instance of the same class that declares the variable or method, A private feature may only be accessed by the class that owns the feature. protected : Is available to all classes in the same package and also available to all subclasses of the class that owns the protected feature.This access is provided even to subclasses that reside in a different package from the class that owns the protected feature. default :What you get by default ie, without any access modifier (ie, public private or protected).It means that it is visible to all within a particular package.|
|What is an abstract class?|
|Abstract class must be extended/subclassesed (to be useful). It serves as a template. A class that is abstract may not be instantiated (ie, you may not call its constructor), abstract class may contain static data. Any class with an abstract method is automatically abstract itself, and must be declared as such. A class may be declared abstract even if it has no abstract methods. This prevents it from being instantiated.|
|What is static in java?|
|Static means one per class, not one for each object no matter how many instance of a class might exist. This means that you can use them without creating an instance of a class. Static methods are implicitly final, because overriding is done based on the type of the object, and static methods are attached to a class, not an object. A static method in a super class can be shadowed by another static method in a subclass, as long as the original method was not declared final. However, you can't override a static method with a nonstatic method. In other words, you can't change a static method into an instance method in a subclass.|
|What is final?|
|A final class can't be extended ie., final class may not be subclassed. A final method can't be overridden when its class is inherited. You can't change value of a final variable (is a constant).|
|What if the main method is declared as private?|
|The program compiles properly but at runtime it will give 'Main method not public' message.|
|What if the static modifier is removed from the signature of the main method?|
|Program compiles. But at runtime throws an error 'NoSuchMethodError'.|
|What if I write static public void instead of public static void?|
|Program compiles and runs properly.|
|What if I do not provide the String array as the argument to the method?|
|Program compiles but throws a runtime error 'NoSuchMethodError'.|
|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. If I do not provide any arguments on the command line, then the String array of Main method will be empty or null? It is empty. But not null.|
|How can one prove that the array is not null but empty using one line of code?|
|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.|
|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.|
|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.|
|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.|
|Do I need to import java.lang package any time? Why ?|
|No. It is by default loaded internally by the JVM.|
|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.|
|What are Checked and UnChecked Exception?|
A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.
What is the value of cot 4π/3 ?
Article-24 of the Indian Constitution ‘Prohibition of employment of children in factories, etc’ deals with?
Article-134A of the Indian Constitution ‘Certificate for appeal to the Supreme Court’ deals with?
Who invented Aspirin?
A larger force on a rotating body results in larger?
What is the unit of the physical quantity, magnetic flux density?
The system of equations 2x + 4y = 6 and 4x + 8y = 8 is ?
|Time and Distance|
A thief is spotted by a policeman from a distacne of 100 m. When the policeman starts the chase, the thief also starts running. If the speed of the theif is 8 km / hour and that of the policeman is 10 km/hour, then how far will the theif have to run before he is overtaken?
Aman and Alok attempted to solve a quadratic equation. Aman made a mistake in writing down the constant term and ended up in roots (4, 3). Alok made a mistake in writing down the coefficient of x to get roots (3, 2). The correct roots of the equation are?
The effective annual rate of interest corresponding to a nominal rate of 22% per annum payable half-yearly is?
|Volume and Surface Area|
If the volume of a cylinder is 2156 cubic cm and height is 14 cm, find its radius?
What is the equation of the line which passes through the points (2, 3) and (- 4, 1)?
In △ABC, the angle bisector of ∠A cuts BC at E. Find length of AC, if lengths of AB, BE and EC are 9 cm, 3.6 cm and 2.4 cm?
In a triangle, the length of the opposite side of the angle which measures 45° is 8√2 cm, what is the length of the side opposite to the angle which measures 90°?
|General Knowledge of India|
The boundary line between India and Pakistan is called?
Which city is located on the banks of the river Mahanadi?
When was the battle of Haldighati fought?
In 1498, which Portuguese explorer discovered a new sea route from Europe to India?
|General Knowledge of India|
Chapchar Kut is a festival of which State?
In chemistry, soap is a salt of a ?
Which of the following is a Direct tax?
Sauria lacertidae is the scientific name of?
Which of the following is a primary function of haemoglobin?
A factory buys 8 machines.3 Machine A, 2 Machine B and rest Machine C. Prices of the machines are 100000, 80000 and 45000 respectively.Calculate the average cost of these machines?
Ticket for an adult is 500 and a child is 200. 1 child goes free with two adults. If a group has 20 adults and 8 children what will be the discount the group get?