Javascript Vector Class

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In Java, there is a wide range of classes used to store certain types of data. Each class has its own characteristics, and the class used to store a data type determines how it can be viewed and manipulated.

The one of the largest Java classes is the Vector class. Vector is an implementation of the List interface and is used to create resizable tables.

This tutorial will show, by referring to examples, how to use the Vector class in Java to create resizable arrays. Additionally, this tutorial will discuss how Vector compares to the ArrayList class, which is very similar to Vector.

Java Interface List

The interface list is used to create datasets in Java. For example, a list might store a list of shoes sold in a shoe store or a list of the names of each employee who works for a bank.

However, because the list is an interface, you cannot create a list object . So if you want to create a list, you have to use one of the classes which extend the list interface. They are: ArrayList, LinkedList, Vector and Stack. This tutorial will focus on how to use the Vector class to create a list object in Java.

Java vector

Vector uses the List interface to create resizable arrays. To create a vector in Java, you can use the following syntax:

Vector vector_name = new Vector <> ();

Or the break in this syntax in its basic elements:

  • vector indicates our program that we want to declare a vector .
  • DataType is the data type our vector will store.
  • vector_name is the name of our vector
  • new vector <> () ;. creates a new vector and assigns it to vector_name variable.

For example, suppose we want to declare a vector that stores all the colors of the lamps sold by our store. We could use this code to declare the vector:

Vector ? Lamp_colors = new Vector> ();

Now we have a vector called lamp_colors which can store all the colors of the lamps sold by our store.

Java Vector Methods

The Java Vector class provides a set of methods used to extract and manipulate data stored in a vector. Let ’s review some of the most important methods offered by the Vector class.

Adding elements to a vector

There are three ways to add elements to vectors. What you use will depend on how you want to add an element to a vector

Add an element to vector

The add () method is used to add an element to a vector. The syntax add () method is:

add (index, elementName);

add () takes two parameters:.

If you want to add an element to the end of a vector, the index parameter is not needed.

Suppose you run a department store chain and create a color list in which a specific desk lamp is sold for our new line of furniture. The manufacturer has just informed us that the orange and blue one will accompany the following order, so we want to add orange and blue to our color list.

We can do this using this code:.

Our code returns:

Vector: [Orange, Blue]

Like you can see, our code added orange and Blue to our lamp_colors vector.

Suppose the manufacturer has us contacted us to say they will also deliver our gray lamps. We want to add gray lamps to the top of our list because we expect them to be more popular than other colors. We could do this using the example above and adding this code:

Our code returns:

Vector: [Gray, Orange, Blue]

In this example, we used the add () to add Gray lamp_colors vector. We specified the index 0 parameter in our code which says add () to add the Gray at the index position 0. In other words, we have added Gray at the start of our vector. Next, we tell our program to print the entire vector

merge vectors

addAll () method is used to add all elements of one vector to another vector.

Suppose we have two lists: the color gamut of the color and the lamp. We want to combine these two listings because our lamp manufacturer has told us that they will be able to produce lamps in any color from our color range. We could use the following code to merge these two vector lists:

Our code returns:

our code first added the colors to the vector of our color range color_range. So we used addAll () to add all the colors of color_range lamp_colors vector. In the last lines of our code, we print to the console both the contents of color_range and lamp_colors

elements of a vector

get () method is used to retrieve a particular element of a vector. get () takes one parameter: the index value of the element you want to retrieve

Suppose our lamp color list is stored alphabetically and we want to retrieve the first item in the list we could do that using. this code:

Our return code:

First element in the list: Black

in our code, we use the get () to retrieve the first element of the lamp_colors vector. We specify the index 0 parameter, which indicates our code to retrieve the first element of the vector, or in other words the element at the position of index 0. Then, we print the first element of the list to the console, preceded by the message first element in the list:.

Remove elements from a vector

There are three methods that can be used to remove elements from a vector: remove () , removeAll () and clear ().

Remove a single element

remove () is used to remove a single element from a vector. remove () a takes one parameter:. the index position of the element you want to remove from a vector

Let dos go to store. Our manufacturer has informed us that they are no longer able to produce our orange lamps, so we need to remove them from our list of colors in which our lamps are sold. We could do it using this code:

Our code returns:

New color list: [Black, Blue, Gray, Pink]

We used the delete () to delete the element at index position 3 in our list. In this case, the value of this element is Orange. Next, we print the modified color list on the console, preceded by the message New color list:.

Remove all elements

removeAll () and clear () methods are used to remove all the elements of a list. Generally, using clear () is preferred because it is more efficient, but you can also use the removeAll () method.

Suppose the manufacturer has decided that they will no longer be able to produce our lamps because they are downsizing their activities. Therefore, we will no longer be selling lamps until we find a new manufacturer. we could use the following list to remove all colors from the lamps we sell:

Our code returns:

New color list: []

us used the clear () to remove all elements from the lamp_colors array. So, in the last line of our code, we printed the sentence New color list. ", Followed by the empty vector

Java Vector and ArrayList

ArrayList and Vector implement the Java List interface. These classes also provide the same methods. However, there are differences between the two classes. The main difference to note is that the Vector class is synchronized, which means that only one thread can access the code at a time. ArrayList, on the other hand, is not synchronized and therefore multiple threads can operate on the list at the same time.

Additional Vector Methods

In addition, there are other methods that can be used to manipulate the data stored in a vector. Here is a reference table with these methods:

< td> Modify an element of a vector
Method name description of
contains () Find a vector for a specific value
iterator () iterate over a vector
set ()
size () Returns the length of a vector
toArray () convert vector from array
toString () convert vector to string

Conclusion

The Vector class is used in Java to store data using the list interface . For example, a vector can be used to store a list of products sold in a store or a list of supplements available at a local drug store.

This tutorial has discussed the basics of the Java vector class, how to create a vector and the main difference between vector and ArrayList. Additionally, this tutorial has illustrated the main methods that can be used to retrieve and manipulate the content of a vector, referring to the examples.

You now have the skills to start using Vector Classes in Java as one! pro

Javascript Vector Class __del__: Questions

How can I make a time delay in Python?

5 answers

I would like to know how to put a time delay in a Python script.

2973

Answer #1

import time
time.sleep(5)   # Delays for 5 seconds. You can also use a float value.

Here is another example where something is run approximately once a minute:

import time
while True:
    print("This prints once a minute.")
    time.sleep(60) # Delay for 1 minute (60 seconds).

2973

Answer #2

You can use the sleep() function in the time module. It can take a float argument for sub-second resolution.

from time import sleep
sleep(0.1) # Time in seconds

How to delete a file or folder in Python?

5 answers

How do I delete a file or folder in Python?

2639

Answer #1


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

Javascript Vector Class __delete__: Questions

2639

Answer #2


Path objects from the Python 3.4+ pathlib module also expose these instance methods:

2639

Answer #3

Python syntax to delete a file

import os
os.remove("/tmp/<file_name>.txt")

Or

import os
os.unlink("/tmp/<file_name>.txt")

Or

pathlib Library for Python version >= 3.4

file_to_rem = pathlib.Path("/tmp/<file_name>.txt")
file_to_rem.unlink()

Path.unlink(missing_ok=False)

Unlink method used to remove the file or the symbolik link.

If missing_ok is false (the default), FileNotFoundError is raised if the path does not exist.
If missing_ok is true, FileNotFoundError exceptions will be ignored (same behavior as the POSIX rm -f command).
Changed in version 3.8: The missing_ok parameter was added.

Best practice

  1. First, check whether the file or folder exists or not then only delete that file. This can be achieved in two ways :
    a. os.path.isfile("/path/to/file")
    b. Use exception handling.

EXAMPLE for os.path.isfile

#!/usr/bin/python
import os
myfile="/tmp/foo.txt"

## If file exists, delete it ##
if os.path.isfile(myfile):
    os.remove(myfile)
else:    ## Show an error ##
    print("Error: %s file not found" % myfile)

Exception Handling

#!/usr/bin/python
import os

## Get input ##
myfile= raw_input("Enter file name to delete: ")

## Try to delete the file ##
try:
    os.remove(myfile)
except OSError as e:  ## if failed, report it back to the user ##
    print ("Error: %s - %s." % (e.filename, e.strerror))

RESPECTIVE OUTPUT

Enter file name to delete : demo.txt
Error: demo.txt - No such file or directory.

Enter file name to delete : rrr.txt
Error: rrr.txt - Operation not permitted.

Enter file name to delete : foo.txt

Python syntax to delete a folder

shutil.rmtree()

Example for shutil.rmtree()

#!/usr/bin/python
import os
import sys
import shutil

# Get directory name
mydir= raw_input("Enter directory name: ")

## Try to remove tree; if failed show an error using try...except on screen
try:
    shutil.rmtree(mydir)
except OSError as e:
    print ("Error: %s - %s." % (e.filename, e.strerror))

Is there a simple way to delete a list element by value?

5 answers

I want to remove a value from a list if it exists in the list (which it may not).

a = [1, 2, 3, 4]
b = a.index(6)

del a[b]
print(a)

The above case (in which it does not exist) shows the following error:

Traceback (most recent call last):
  File "D:zjm_codea.py", line 6, in <module>
    b = a.index(6)
ValueError: list.index(x): x not in list

So I have to do this:

a = [1, 2, 3, 4]

try:
    b = a.index(6)
    del a[b]
except:
    pass

print(a)

But is there not a simpler way to do this?

1055

Answer #1

To remove an element"s first occurrence in a list, simply use list.remove:

>>> a = ["a", "b", "c", "d"]
>>> a.remove("b")
>>> print(a)
["a", "c", "d"]

Mind that it does not remove all occurrences of your element. Use a list comprehension for that.

>>> a = [10, 20, 30, 40, 20, 30, 40, 20, 70, 20]
>>> a = [x for x in a if x != 20]
>>> print(a)
[10, 30, 40, 30, 40, 70]

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