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Quiz based on Digital Principles and Computer Organization

1) Base of hexadecimal number system? Answer : 16 2) Universal gate in digital logic? Answer : NAND 3) Memory type that is non-volatile? Answer : ROM 4) Basic building block of digital circuits? Answer : Gate 5) Device used for data storage in sequential circuits? Answer : Flip-flop 6) Architecture with shared memory for instructions and data? Answer : von Neumann 7) The smallest unit of data in computing? Answer : Bit 8) Unit that performs arithmetic operations in a CPU? Answer : ALU 9) Memory faster than main memory but smaller in size? Answer : Cache 10) System cycle that includes fetch, decode, and execute? Answer : Instruction 11) Type of circuit where output depends on present input only? Answer : Combinational 12) The binary equivalent of decimal 10? Answer : 1010 13) Memory used for high-speed temporary storage in a CPU? Answer : Register 14) Method of representing negative numbers in binary? Answer : Two's complement 15) Gate that inverts its input signal? Answer : NOT 16)...

Java important question - 12

What is the use of final keyword in java ?
          final keyword is used in different contexts. First of all, final is a non-access modifier applicable only to a variable, method or a class. Following are different contexts where final is used,
a) Final variable - To create constant variable.
When a variable is declared with final keyword, it's value can't be modified, essentially a constant. This also means that you must initialize a final variable. If the final variable is reference this means that the variable cannot be rebound to reference another object, but the internal state of the object pointed by that reference variable can be changed. i.e. you can add or remove elements from final array or final collection. It is good practice to represent final variables in all uppercase, using underscore to separate words.
Java interface variables are by default final and static.
b) Final methods - Prevent method overridding.
We can use the final keyword with methods to make sure child classes can't override it.
c) Final Classes - Prevent inheritance.
Final keyword is used in class to make sure no other class can extend it , for example String class is final and we can't extend it.

What purpose does the keyword final, finally and finalize fulfill ?
Final :
          Final is used to apply restrictions on class, method and variable. Final class can't be inherited, final method can't be overridden and final variable value cannot be changed.
Finally :
          Finally is used to place important code,it will be executed whether exception is handled or not.
Finalize :
          Finalize is used to perform cleanup processing just before object is garbage collected.

What are the uses of a final class ?
          There are two uses of a final class,
1. To prevent inheritance :
          A class declared with final keyword cannot be extended. For example, all wrapper classes like Integer, Float etc. are final classes. We can not extend them.
final class A
{
// Methods and fields
}
// The following class is illegal
class B extends A
{
// Compile-error! Can't subclass A
}

2. To create an immutable class :
          The other use of final with classes is to create an immutable class like the predefined String class. You can not make a class immutable without making it final.

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