使用输入和输出流读取和写入文件：

//Coded By Anurag Goel
//Reading And Writing Files
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;


public class WriteAFile {
    public static void main(String args[]) {
        try {
            byte array [] = {'1','a','2','b','5'};
            OutputStream os = new FileOutputStream("test.txt");
            for(int x=0; x < array.length ; x++) {
                os.write( array[x] ); // Writes the bytes
            }
            os.close();

            InputStream is = new FileInputStream("test.txt");
            int size = is.available();

            for(int i=0; i< size; i++) {
                System.out.print((char)is.read() + " ");
            }
            is.close();
        } catch(IOException e) {
            System.out.print("Exception");
        }
    }
}

用Java创建和写入文件的一种非常简单的方法：

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;

public class CreateFiles {

    public static void main(String[] args) {
        try{
            // Create new file
            String content = "This is the content to write into create file";
            String path="D:\\a\\hi.txt";
            File file = new File(path);

            // If file doesn't exists, then create it
            if (!file.exists()) {
                file.createNewFile();
            }

            FileWriter fw = new FileWriter(file.getAbsoluteFile());
            BufferedWriter bw = new BufferedWriter(fw);

            // Write in file
            bw.write(content);

            // Close connection
            bw.close();
        }
        catch(Exception e){
            System.out.println(e);
        }
    }
}

如果您已经有了要写入文件的内容（而不是动态生成的），那么Java7中作为本机I/O的一部分添加的java.nio.file.Files提供了实现目标的最简单、最有效的方法。

基本上，创建和写入文件只需一行，而且只需一个简单的方法调用！

以下示例创建并写入6个不同的文件，以展示如何使用它：

Charset utf8 = StandardCharsets.UTF_8;
List<String> lines = Arrays.asList("1st line", "2nd line");
byte[] data = {1, 2, 3, 4, 5};

try {
    Files.write(Paths.get("file1.bin"), data);
    Files.write(Paths.get("file2.bin"), data,
            StandardOpenOption.CREATE, StandardOpenOption.APPEND);
    Files.write(Paths.get("file3.txt"), "content".getBytes());
    Files.write(Paths.get("file4.txt"), "content".getBytes(utf8));
    Files.write(Paths.get("file5.txt"), lines, utf8);
    Files.write(Paths.get("file6.txt"), lines, utf8,
            StandardOpenOption.CREATE, StandardOpenOption.APPEND);
} catch (IOException e) {
    e.printStackTrace();
}

    public static void writefromFile(ArrayList<String> lines, String destPath) {
        FileWriter fw;
        try {
            fw = new FileWriter(destPath);
            for (String str : lines) {
                fw.write(str);
            }
            fw.close();
         } catch (IOException ex) {
            JOptionPane.showMessageDialog("ERROR: exception was: " + ex.toString());
        }
        File f = new File(destPath);
        f.setExecutable(true);
    }

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;

public class FileWriterExample {
    public static void main(String [] args) {
        FileWriter fw= null;
        File file =null;
        try {
            file=new File("WriteFile.txt");
            if(!file.exists()) {
                file.createNewFile();
            }
            fw = new FileWriter(file);
            fw.write("This is an string written to a file");
            fw.flush();
            fw.close();
            System.out.println("File written Succesfully");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

如果出于某种原因想要将创建和编写行为分开，那么Java中的touch等价物是

try {
   //create a file named "testfile.txt" in the current working directory
   File myFile = new File("testfile.txt");
   if ( myFile.createNewFile() ) {
      System.out.println("Success!");
   } else {
      System.out.println("Failure!");
   }
} catch ( IOException ioe ) { ioe.printStackTrace(); }

createNewFile（）执行存在性检查，并自动创建文件。例如，如果您希望在写入文件之前确保自己是文件的创建者，这可能很有用。