Here is a table from OCP Java SE 8 Programmer II Exam Guide (Exam 1Z0-809) that summarizes the basic classes in file io.

java.io Class	Extends From	Key Constructor(s)	Key Methods
`File`	`Object`	`File, String` `String` `String, String`	`createNewFile()` `delete()` `exists()` `isDirectory()` `isFile()` `list()` `mkdir()` `renameTo()`
`FileWriter`	`Writer`	`File` `String`	`close()` `flush()` `write()`
`BufferedWriter`	`Writer`	`Writer`	`close()` `flush()` `newLine()` `write()`
`PrintWriter`	`Writer`	`File` `String` `OuputStream` `Writer`	`close()` `flush()` `format()` `printf()` `print()` `println()` `write()`
`FileOutputStream`	`OutputStream`	`File` `String`	`close()` `write()`
`FileReader`	`Reader`	`File` `String`	`read()`
`BufferedReader`	`Reader`	`Reader`	`read()` `readLine()`
`FileInputStream`	`InputStream`	`File` `String`	`read()` `close()`

Examples

import java.io.*;

class Writer1 {
    public static void main(String... args) {
        try {
            boolean newFile = false;
            File file = new File("fileWrite1.txt");
            System.out.println(file.exists());
            newFile = file.createNewFile();
            System.out.println(newFile);
            System.out.println(file.exists());
        } catch(IOException e) {}

    }
}

class Writer2 {
    public static void main(String... args) {
        char[] in = new char[50];
        int size = 0;
        try {
            File file = new File("fileWrite2.txt");
            FileWriter fw = new FileWriter(file);
            fw.write("howdy
folks
");
            fw.flush();
            fw.close();
            FileReader fr = new FileReader(file);
            size = fr.read(in);
            System.out.print(size + " ");
            for(char c: in) {
                System.out.print(c);
            }
            fr.close();
        } catch(IOException e) { }
    }
}

class Writer3 {
    public static void main(String... args) {
        byte[] in = new byte[50];
        int size = 0;
        File file = new File("fileWrite3.txt");
        try(FileOutputStream outStream = new FileOutputStream(file);
            FileInputStream inStream = new FileInputStream(file)) {
            String s = "howdy
folks
";
            outStream.write(s.getBytes());
            outStream.flush();

            size = inStream.read(in);
            System.out.print(size + " ");
            for(byte b: in) {
                System.out.print((char) b);
            }
        } catch(IOException e) {}
    }
}

class Writer4 {
    public static void main(String... args) {
        File file = new File("fileWrite4.txt");
        try(PrintWriter pw = new PrintWriter(file);
            BufferedReader br = new BufferedReader(new FileReader(file))) {
            pw.println("howdy");
            pw.println("folks");
            pw.flush();
            
            String line = null;
            while(true) {
                line = br.readLine();
                if (line == null) break;
                System.out.println(line);
            }

        } catch(IOException e) {}    
    }
}

Zhenyang Hua

Useful File java.io Mini API

Examples

Read on GitHub