Match the definition

"The ability to create methods with the same name that are in different classes" is known as ________.

Jlenok [28]

Answer:

Polymorphism

Explanation:

Polymorphism is the ability of an object to take multiple forms. It is an important concept of Object Oriented Programming. Polymorphism is used in Object Oriented Programming when a reference of a parent class is used to refer to a child class object. It allows to perform a single action in different ways. For example a person can possess different characteristics at the same time. A person can be a father, husband, employee or student. The same person can have different behaviors in different circumstances.

Example:

Suppose there is class Animal with a procedure sound(). This method can have different implementation for different animals. For this purpose lets take two derived classes Cow and Cat that extend the Animal class (parent/base class). Now the method sound() can be used in different ways for Cow and Cat.

public class Animal{

public void sound(){

System.out.println("Animal is making a sound"); } }

public class Cat extends Animal{

public void sound(){

System.out.println("Meow"); } }

The output is Meow. The same method sound() is used for cat subclass.

public class Cow extends Animal {

public void sound(){

cout<<"Mooo"; }}

The output is Mooo. The method sound() is used for a Cow subclass which returns the sound of Cow in output.

So the same function i.e. sound() behaves differently in different situations which shows Polymorphism.

Polymorphism has 2 types.

One is compile time polymorphism which is called overloading. In method overloading a class can have more than one functions with same name but different parameters. Methods can be overloaded by change in number or type arguments. For example overloading a function method() can take the following forms in which the name remains the same and parameters are different.

void method(int a)

void method(float a)

void method(float a, float b)

Second type is run time polymorphism which is called overriding. Method overriding is when a method declared in derived class is already present in base class. In this way derived/child class can give its own implementation to base/parent class method. Method present in base class is called overridden and that in subclass is called overriding method. The example of Animal Cow and Cat given above is an example of overriding.

6 0

3 years ago

Describe Relational Query Languages and Operations.

Lelechka [254]

Answer:

Relational query language is the language that is used in the queries of the relational databases that has rows and columns in table. The user or client presents a request for gaining the information from the database. The relationships in the database are defined in numerous ways which creates the query.

This language can be procedural form or non-procedural form.The operations performed by this language are communication with the relational database, analyzing the relationships between the entities of database,splitting the request from client and then execution of that request is done by database management system(DBMS), etc.

7 0

3 years ago

One of the earlier applications of crypto-graphic hash functions was the storage of passwords to authenticate usersin computer s

vagabundo [1.1K]

Answer: provided in the explanation part.

Explanation:

This is actually quite long but nevertheless i will make it as basic as possible.

Question (a)

Attack A:

One way property of hash means that we can't find the input string if given the hash value. The calculation of hash from input string is possible but it is not possible to calculate the input string when given the hash. If the hash function is properly created to have one-way property then there is no way of finding the exact input string. So this attack won't work as the one-way property of hash function can't be broken if the hash function is properly created.

Attack B:

Suppose h() is the hash function. And h(x) = m where x is the string and m is the hash. Then trying to find another string y such that h(y) = m is called finding out the second pre-image of the hash.

Although we can't know the exact initial string for sure, we can by using brute force method find out a second preimage.

This attack will take a very long time. It has the time complexity of 2n. It requires the attacker to have an idea about the kind of passwords that might be used and then brute force all of them to find the string that has the same hash. Each try will have a chance of 1/2n to succeed.

Rainbow attack using rainbow table is often used for such brute-force attack. This comprises a rainbow table which contains passwords and their pre-hashed values.

Therefore, it is not possible to determine the second preimages of h so easily.

Attack C:

Collisions refer to finding out m and m' without knowing any of them. Finding out collisions is easier than finding preimages. This is because after finding out 2n pairs of input/output. The probability of two of them having the same output or hash becomes very high. The disadvantage is that we can't decide which user's hash to break. However, if I do not care about a particular user but want to get as many passwords as possible, then this method is the most feasible.

It has the time complexity of 2n/2.

Hence, this is the attack which has the most success rate in this scenario.

Question (b)

The brute force way of finding out the password usually involves using a rainbow attack. It comprises a rainbow table with millions of passwords and their hashes already computed. By matching that table against the database, the password can be recovered.

Therefore it is often preferred to salt the password. It means we add some random text to the password before calculating the hash.

The salts are usually long strings. Although users usually do not select long passwords, so a rainbow table with hashes of smaller passwords is feasible. But once salt is used, the rainbow table must accommodate for the salt also. This makes it difficult computationally. Although password might be found in the rainbow table. The salt can be anything and thus, make brute-force a LOT more difficult computationally.

Therefore salt is preferred to be added to passwords before computing their hash value.

Question (c)

A hash output length of 80 means there can be exactly 280 different hash values. This means there is at least one collision if 280+1 random strings are hashed because 280 values are used to accommodate all the possible strings. It is not hard with today's computation power to do match against more than this many strings. And doing so increases the probability of exposing a probable password of a user.

Hence, 80 is not a very secure value for the hash length.

cheers i hope this helps!!!!

6 0

4 years ago

1. What does it mean to say that a country’s land area is positively correlated with its population?

disa [49]

For 1.
Positive correlation means if you plot a country's population and land size on a graph. There would be a linear regression line that's sloping upwards.

Since it's a scatterplot, there will be some that fall out of the line, but most of them should be on the line.

It's (A)

For 2.
An outlier is a datapoint that's far, FAR away from the others, so it's (B)

For 3. (A), it's a single line-of-best fit that runs through the middle of the cluster of data points.

5 0

3 years ago

Read 2 more answers

2.4 Code Practice: Question 1

USPshnik [31]

Answer:

num = float(input("Enter a number : "))

ab = abs(num)

sqrt = float(ab ** 0.5)

print(sqrt)

Explanation:

6 0

3 years ago