Java文件 (Java files)

The file is a class of java.io package.

该文件是java.io包的类。

If we create a file then we need to remember one thing before creating a file. First, we need to check whether a file exists of the same name or not. If a file of the same name exists then we can’t create a file of same name else we can create a file of same.

如果创建文件，那么在创建文件之前我们需要记住一件事。 首先，我们需要检查文件是否存在相同名称。 如果存在同名文件，那么我们将无法创建同名文件，否则我们将创建同名文件。

We will study three things:

我们将研究三件事：

• Creating a file

  建立档案

• Reading a file

  读取文件

• Writing a file

  写文件

1) Creating a file

1)创建一个文件

To create a file by using createNewFile() method and the return type of this method is Boolean so it returns true or false. It returns true during successful creation of the file and It returns false during the creation of file failure.

要使用createNewFile()方法创建文件，并且此方法的返回类型为Boolean，因此它将返回true或false。 成功创建文件时返回true，创建文件失败时返回false。

Example:

例：

// import the File class because we will use File class methods
import java.io.File;
//import the Exception class because it may raise
//an exception when working with files
import java.lang.Exception;
public class CreateFile {public static void main(String[] args) {try {// Specify the path of file and we use double slashes
// to escape '\' character sequence for windows otherwise
// it will be considerable as url.
File file = new File("C:\\Users\\computer clinic\\OneDrive\\Articles\\myjava.txt");
// createNewFile() returns true if file is successfully
// created and then we will get the name of the file
// using getName() method and return false if the file
// is already exists then we will get the message
if (file.createNewFile()) {System.out.println("File created: " + file.getName());
} else {System.out.println("File already exists of same name!! Please try to create from other name ");
}
} catch (Exception e) {System.out.println("An error occurred.");
e.printStackTrace();
}
}
}

Output

输出量

D:\Programs>javac CreateFile.java
D:\Programs>java
File created: myjava.txt

2) Writing a file

2)写文件

To write a file by using write() method of FileWriter class.

使用FileWriter类的write()方法写入文件。

Example:

例：

// import the FileWriter class because
// we will use FileWriter class methods write()
import java.io.FileWriter;
//import the Exception class because it may raise
// an exception when working with files
import java.lang.Exception;
public class WriteFile {public static void main(String[] args) {try {// Create an object of FileWriter class
FileWriter fw = new FileWriter("C:\\Users\\computer clinic\\OneDrive\\Articles\\myjava.txt ");
// To write a file by using write() method
fw.write("We are going to write a file by using write()");
// After writing a file then we need to close safely
fw.close();
//After successfully written of file then display a message for the user
System.out.println("File has been written successfully");
} catch (Exception e) {System.out.println("An error occurred");
e.printStackTrace();
}
}
}

Output

输出量

D:\Programs>javac WriteFile.java
D:\Programs>java WriteFile
File has been written successfully

3) Reading a file

3)读取文件

To read a file by using nextLine() method of Scanner class.

通过使用Scanner类的nextLine()方法读取文件。

Example:

例：

// import the File class because we will
// use File class methods
import java.io.File;
//import the Exception class because it may
// raise an exception when working with files
import java.lang.Exception;
// import the Scanner class to read file from user
import java.util.Scanner;
public class ReadFile {public static void main(String[] args) {try {File fr = new File("C:\\Users\\computer clinic\\OneDrive\\Articles\\myjava.txt ");
Scanner sc = new Scanner(fr);
while (sc.hasNextLine()) {String file_read = sc.nextLine();
System.out.println(file_read);
}
sc.close();
} catch (Exception e) {System.out.println("An error occurred.");
e.printStackTrace();
}
}
}

Output

输出量

D:\Programs>javac ReadFile.java
D:\Programs>java ReadFile
We are going to write a file by using write()

翻译自: https://www.includehelp.com/java/what-are-java-files.aspx