How To Create A File Object In Javascript

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There are several scenarios in which you will want to work with files in Java. For example, you might create a file to store the output of a program, or perhaps decide to read data from a file which is then processed by a program.

C ’ is ; This is where the java.io library comes in. The java.io library provides a number of methods used for working with files in Java.

This tutorial will explain how to use the Java File, FileReader, and FileWriter classes and their main methods. This tutorial will also refer to an example of each of these methods used, to show how to use them in your code.

Java files

Files are items on a computer that store specific information. For example, a file might store a list of student names in a math class or a list of ingredients used to bake a coffee cake. Directories, on the other hand, are folders that store collections of files and other directories.

The java.io library includes a number of packages that can be used to work with files and directories in Java. For this tutorial, we’ll focus on the Java File, FileReader, and FileWriter packages.

Since the methods offered by these packages are part of an external package, we must first import them before we can use them in our code.

Here is the code we can use to import the File, FileReader and FileWriter classes into our program:

import java.io.File;

import java .io.FileReader ;

import java.io.FileWriter ;

Now that we know how to import the Java class file we will be working with in this tutorial, we are ready to continue.

Create a Java file

The Java File class is used to create an empty file in Java.

Before you can create a file, however, you must create a File object. The file object is a representation of a specific file or folder in our code. However, the file object does not create a file itself. We need to create a file object first, so that we can use it to create a file.

Here is the syntax we can use to create an object file in Java:

File fileName = newFile (String filePath);

In this unholy ex , we created a filesystem object called fileName. This file object refers to the file or folder stored in the file path specified in the filePath variable.

To create a file in Java, you can use the createNewFile () method. createNewFile () creates a new file in the specified path. The method returns true if a new file is created and false if a file already exists in the specified location.

Suppose we create a data analysis program that analyzes historical stock performance for the S&P 500 in 2019. Before analyzing our data, we want to create a new file that will store the information created by our program. We could use this code to create the file that will store the results of our analysis:

When we run our code, a file is created in the path /home/data_analysis/2019sandp500/result.txt. Then the following response is returned to the console:

The result file has been created.

However, if the file we are trying to create already exists, this message would be returned to the console:

The file results already exist.

Let’s analyze our code. First, let’s import the java.io.File method which includes the file methods we’ll be using in our code. Next, we create a class called CreateFile which stores the code for our program.

In the first line of our main program, we create a file object called resultsFile, which represents the file in the / home / data_analysis file path /2019sandp500/result.txt. Next, we use the createNewFile () method to create a new file in the specified file path. The boolean result of the createNewFile () method is stored in the fileCreated variable.

On the next line, we create an if statement. If fileCreated is equal to true, the message The result file has been created. it will be printed on the console; otherwise, the message The result file already exists. will be printed on the console. In this case the results file does not exist, so our code created the new file and printed The result file was created. in the console.

Read a Java file

The read () in the Java FileRea class der is used to read the contents of a Java file.

Suppose we have a file called /home/data_analysis/2019sandp500/raw_message.txt that we want to access in our code. This file contains the following text:

JAVA S&P 500 ANALYSIS PROGRAM

We could read this file using code next:

Our code returns:

JAVA S&P 500 ANALYSIS PROGRAM

In our program, used the FileReader class to create a file object representing the contents of the file stored in /home/data_analysis/2019sandp500/raw_message.txt. Next, we used the read () method to read the contents of the file into an array. Finally, we printed the contents of the array to the console and used close () to close our file.

Write to a Java file

The write () method of the FileWriter package is used to write to a file in Java.

Suppose we want to write today’s date at the top of the results file that stores the results of our data analysis program. This file is stored in the /home/data_analysis/2019sandp500/results.txt file path. We could do it using this code:

Our code writes Thursday March 12th in the file /home/data_analysis/2019sandp500/results.txt and prints what follow to console:

The date was written to the file.

Here is the content of the results.txt file that we wrote in our program:

Thursday March 12th

In our example above, we used the FileWriter method to write a sentence to a file in Java. First, we have declared a variable called writeToFile () which creates a representation of the file stored in the file path /home/data_analysis/2019sandp500/results.txt. The write () is used to write a string to a file, so we use the close () method to close the file.

Delete a file in Java

The Java File package provides a method used to delete a file or a directory - delete ().

delete () returns true if the specified file is deleted and false if the file does not exist. hode delete () can only delete dir Directory without content.

Suppose we want to delete the results.txt file at the start of our program so that we can write new data to the file later in our program. We could do it using this code:

Our code deletes the contents of the results.txt file and prints the following to the console:

In this example, we’ve created a File object called results that represents the contents of the results.txt file. Next, we used the delete () method to delete the contents of the file.

If the results.txt file was deleted successfully - as in the example above - The message results.txt was deleted. is printed on the console. Otherwise, results.txt was not deleted. is printed on the console.

Conclusion

The Java File package is used to create and delete files, the FileReader package is used to read the contents of a file, and the FileWriter package is used to write to a file.

This tutorial shows, by referring to examples, how to use the Java File, FileReader and FileWriter packages to work with files in your code. You are now ready to start working with files in Java like a professional programmer !

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How To Create A File Object In Javascript __del__: Questions

__del__

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 Create A File Object In Javascript __del__: Questions

__del__

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:

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))

__delete__

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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