There are a number of scenarios where you\u2019ll want to work with files in Java. For instance, you may want to create a file to store the output of a program, or perhaps you decide that you want to read data from a file which is then processed by a program.
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That\u2019s where the java.io library comes in. The java.io library offers a number of methods that are used to work with files in Java.
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This tutorial will discuss how to use the Java File, FileReader, and FileWriter classes and their core methods. This tutorial will also refer to an example of each of these methods in use, to demonstrate how you can use them in your code.
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Files are items in a computer that store a particular piece of information. For instance, a file could 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.
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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 are going to focus on the Java File, FileReader, and FileWriter packages.
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Because the methods offered by these packages are part of an external package, we first need to import these packages before we can use them in our code.
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Here\u2019s the code we can use to import the File, FileReader, and FileWriter classes into our program:
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Now that we know how to import the Java file classes we will be working with in this tutorial, we\u2019re ready to proceed. The Java File class is used to create an empty file in Java. Before we can create a file, however, we need to create a File object. The file object is a representation of a specific file or folder in our code. That said, the file object does not create a file in itself. We first need to create a file object, then we can use it to create a file. Here\u2019s the syntax we can use to create a file object in Java: In this example, we have created a file system object called To create a file in Java, we can use the Suppose we are creating a data analysis program that analyzes historical stock performance for the S&P 500 in 2019. Before we analyze our data, we want to create a new file that will store the insights our program creates. We could use this code to create the file which will store the results of our analysis: When we run our code, a file at the path However, if the file we are trying to create already exists, this message would be returned to the console: Let\u2019s break down our code. First, we import the On the first line of our main program, we create a file object called On the next line, we create an The Suppose we have a file called We could read this file using the following code: Our code returns: JAVA S&P 500 ANALYSIS PROGRAM In our program, we used the FileReader class to create a file object representing the contents of the file stored at The Suppose we want to write today\u2019s date to the top of the results file that stores the results of our data analysis program. This file is stored at the file path Our code writes Here are the contents of the results.txt file which we wrote in our program: In our above example, we used the The Java File package offers a method that is used to delete a file or directory\u2014 Suppose we want to delete the Our code deletes the contents of the results.txt file and prints the following to the console:<\/p>\n\n\n\n In this example, we created an object of File called results which represents the contents of the results.txt file. Then, we used the If the results.txt file was successfully deleted — like it was in the above example — the message 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 discussed, with reference to examples, how to use the File, FileReader, and FileWriter Java packages to work with files in your code. Now you\u2019re ready to start working with files in Java like a professional programmer!<\/p>\n","protected":false},"excerpt":{"rendered":"There are a number of scenarios where you\u2019ll want to work with files in Java. For instance, you may want to create a file to store the output of a program, or perhaps you decide that you want to read data from a file which is then processed by a program. That\u2019s where the java.io…","protected":false},"author":240,"featured_media":13479,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[17289],"tags":[],"class_list":{"0":"post-13478","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-java"},"acf":{"post_sub_title":"","sprint_id":"","query_class":"Java","school_sft":"","parent_sft":"","school_privacy_policy":"","has_review":"","is_sponser_post":"","is_guest_post":""},"yoast_head":"\nimport java.io.File;<\/code><\/p>\n\n\n\nimport java.io.FileReader;<\/code><\/p>\n\n\n\nimport java.io.FileWriter;
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<\/p>\n\n\n\nCreate a Java File<\/h2>\n\n\n\n
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<\/p>\n\n\n\nFile fileName = newFile(String filePath);
<\/code><\/p>\n\n\n\nfileName<\/code>. This file object relates to the file or folder stored at the file path we specified in the filePath<\/code> variable.
<\/p>\n\n\n\n createNewFile()<\/code> method. createNewFile() <\/code>creates a new file at the file path you specify. The method returns true if a new file is created and false if there is already a file in the location you have specified.
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<\/p>\n\n\n\nimport java.io.File;\nclass CreateFile {\n\tpublic static void main(String[] args) {\n\t\tFile resultsFile = new File(\"\/home\/data_analysis\/2019sandp500\/result.txt\");\n\t\tboolean fileCreated = resultsFile.createNewFile();\n\t\tif (fileCreated) {\n\t\t\tSystem.out.println(\"The results file has been created.\");\n\t\t} else {\n\t\t\tSystem.out.println(\"The results file already exists.\");\n\t\t}\n\t}\n}<\/pre><\/div>\n\n\n\n\/home\/data_analysis\/2019sandp500\/result.txt<\/code> is created. Then, the following response is returned to the console:
<\/p>\n\n\n\nThe results file has been created.
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<\/p>\n\n\n\nThe results file already exists.
<\/code><\/p>\n\n\n\n java.io.File<\/code> method which includes the file methods we will use in our code. Then we create a class called CreateFile<\/code> which stores the code for our program.
<\/p>\n\n\n\nresultsFile<\/code>, which represents the file at the file path \/home\/data_analysis\/2019sandp500\/result.txt<\/code>. Then we use the createNewFile() <\/code>method to create a new file at the file path we specified. The boolean result of the createNewFile()<\/code> method is stored in the variable fileCreated.
<\/p>\n\n\n\nif<\/code> statement. If fileCreated is equal to true, the message The results file has been created<\/code>. will be printed to the console; otherwise, the message The results file already exists<\/code>. will be printed to the console. In this case, the results file does not exist, so our code created the new file and printed The results file has been created.<\/code> to the console.
<\/p>\n\n\n\nRead a Java File<\/h2>\n\n\n\n
read()<\/code> method in the Java FileReader class is used to read the contents of a Java file.
<\/p>\n\n\n\n\/home\/data_analysis\/2019sandp500\/raw_message.txt<\/code> that we want to access in our code. This file contains the following text:
<\/p>\n\n\n\nJAVA S&P 500 ANALYSIS PROGRAM
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<\/p>\n\n\n\nimport java.io.FileReader;\nclass Main {\n\tpublic static void main(String[] args) {\n\t\tchar[] array = new char[100];\n\t\ttry {\n\t\tFileReader fileContents = new FileReader(\"\/home\/data_analysis\/2019sandp500\/raw_message.txt\");\n\t\tfileContents.read(array);\n\t\tSystem.out.println(array);\n\t\tfileContents.close();\n\t\t} catch(Exception error) {\n\t\t\terror.getStackTrace();\n\t\t}\n\t}\n}<\/pre><\/div>\n\n\n\n
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<\/p>\n\n\n\n\/home\/data_analysis\/2019sandp500\/raw_message.txt.<\/code> Then, we used the read() <\/code>method to read the contents of the file into an array. Finally, we printed out the contents of the array to the console and used close()<\/code> to close our file.
<\/p>\n\n\n\nWrite to a Java File<\/h2>\n\n\n\n
write() <\/code>method from the FileWriter<\/code> package is used to write to a file in Java.
<\/p>\n\n\n\n\/home\/data_analysis\/2019sandp500\/results.txt<\/code>. We could do so using this code:
<\/p>\n\n\n\nimport java.io.FileWriter;\nclass Main {\n\tpublic static void main(String args[]) {\n\t\tString date = \"Thursday, March 12th\";\n\t\ttry {\n\t\t\tFileWriter writeToFile = new FileWriter(\"\/home\/data_analysis\/2019sandp500\/results.txt\");\n\t\t\twriteToFile.write(date);\n\t\t\t\n\t\t\twriteToFile.close();\n\t\t\tSystem.out.println(\"The date has been written to the file.\");\n\t\t} catch (Exception error) {\n\t\t\terror.getStackTrace();\n\t\t}\n\t}<\/pre><\/div>\n\n\n\nThursday, March 12th<\/code> to the file \/home\/data_analysis\/2019sandp500\/results.txt<\/code> and prints the following to the console:
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<\/p>\n\n\n\nThursday, March 12th
<\/code><\/p>\n\n\n\nFileWriter<\/code> method to write a sentence to a file in Java. First, we declared a variable called writeToFile() <\/code>which creates a representation of the file stored at the file path \/home\/data_analysis\/2019sandp500\/results.txt<\/code>. The write() <\/code>method is used to write a string to a file, then we use the close() method<\/code> to close the file.
<\/p>\n\n\n\nDelete a File in Java<\/h2>\n\n\n\n
delete().<\/code>
<\/p>\n\n\n\ndelete() <\/code>returns true if the file specified is deleted, and false if the file does not exist. In addition, the delete() <\/code>method can only delete directories with no contents.
<\/p>\n\n\n\nresults.txt<\/code> file at the start of our program so that we can write new data to the file later in our program. We could do so using this code:
<\/p>\n\n\n\nimport java.io.File;\nclass Main {\n\tpublic static void main(String[] args) {\n\t\tFile results = newFile(\"\/home\/data_analysis\/2019sandp500\/results.txt\");\n\t\tboolean deleteFile = results.delete();\n\t\tif (deleteFile) {\n\t\t\tSystem.out.println(\"results.txt has been deleted.\");\n\t\t} else {\n\t\t\tSystem.out.println(\"results.txt has not been deleted.\");\n\t\t}\n\t}\n}<\/pre><\/div>\n\n\n\nresults.txt has been deleted.<\/pre><\/div>\n\n\n\n
delete()<\/code> method to delete the contents of the file.
<\/p>\n\n\n\nresults.txt has been deleted<\/code>. is printed to the console. Otherwise, results.txt has not been deleted<\/code>. is printed to the console.
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