File I/O

/MyDocuments/BookeProject/Book.java

public class ThrowSample {
   public static void main(String[] args) throws java.io.FileNotFoundException {
      File inputFile = new File("doubles.txt"); 
      Scanner inDouble = new Scanner(inputFile);
      double largest = inDouble.nextDouble();
      while (inDouble.hasNextDouble()) {
         double input = inDouble.nextDouble();
         if (input > largest) 
            largest = input;
      }
      System.out.println("Largest value: " + largest);
   }
}

public class CatchSample {
   public static void main(String[] args) {
      try {
         File inputFile = new File("doubles.txt"); 
         Scanner inDouble = new Scanner(inputFile);
         double largest = inDouble.nextDouble();
         while (inDouble.hasNextDouble()) {
            double input = inDouble.nextDouble();
            if (input > largest) 
               largest = input;
         }
         System.out.println("Largest value: " + largest);
      } catch (Exception e) {
          e.printStackTrace();
          System.exit(1);
      }
   }
}

Student
Coletta
1
3.9
Person
Zac
28
0
Student
Emily
22
4.0
Student
Homer
3.3

public class Person {
    private String name;
    private int age;
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    @Override
    public String toString() { return name+" " + age; }

    @Override
    public boolean equals(Object p) { 
        return this.name.equals(((Person)p).name) &&
               this.age == ((Person)p).age; 
    }
}

public class Student extends Person {
    public double gpa;
    public Student(String name, int age, double gpa) {
        super(name, age);
        this.gpa = gpa;
    }
}

import java.io.File;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.Scanner;
import java.io.BufferedWriter;
import java.io.PrintWriter;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.StandardOpenOption;

public class PeopleDBGet
{
    /**
     * Fills an ArrayList<Person> with information in a file
     * Each person/student in the file has 4 lines
     * Line 1: Either Person or Student
     * Line 2: name
     * Line 3: age
     * Line 4: gpa (0 for Person
     * @param fileName name of file
     * @return ArrayList<Person> with information from file
     */
    public static ArrayList<Person> personDBRead(String fileName) throws FileNotFoundException {
        ArrayList<Person> pal = new ArrayList<Person>();
        File inputFile = new File(fileName);
        Scanner in = new Scanner(inputFile);
        boolean goon = true;
        while (goon) {
            String line = "";
            if (in.hasNext()) {
                String type = in.nextLine();
                String name = in.nextLine();
                int age = Integer.parseInt(in.nextLine());
                double gpa = Double.parseDouble(in.nextLine());
                if (type.equals("Student"))
                    pal.add(new Student(name, age, gpa));
                else
                    pal.add(new Person(name, age));
            }
            else
                goon = false;
        }
        return pal;
    }
    
    public static void main(String[] args) throws FileNotFoundException {
        String fileName = "people.txt";
        if (args.length != 0)
            fileName = args[0];
                    
        ArrayList<Person> pal = personDBRead(fileName);
        for (Person p : pal) {
            System.out.print(p + " ");
            if (p instanceof Student)
                System.out.println(((Student)p).gpa);
            else
                System.out.println();
        }
        // Add a new person or student to our DB
        Scanner in = new Scanner(System.in);
        System.out.print("Enter Student or Person: ");
        String type = in.nextLine();
        System.out.print("Enter name: ");
        String name = in.nextLine();
        System.out.print("Enter age: ");
        String age = in.nextLine();
        System.out.print("Enter gpa (0 for Person): ");
        String gpa = in.nextLine();
        Path file = Paths.get(fileName);
        Charset charset = Charset.forName("US-ASCII");
        PrintWriter out = null;
        BufferedWriter writer = null;
        try {
            writer = Files.newBufferedWriter(file, charset,
                                             StandardOpenOption.WRITE, 
                                             StandardOpenOption.APPEND,
                                             StandardOpenOption.CREATE);
            out = new PrintWriter(writer, true);  // true indicates to append
            out.println(type);
            out.println(name);
            out.println(age);
            out.println(gpa);
            out.close();
        } catch (IOException x) {
            System.err.format("IOException: %s%n", x);
        }
    }      
}

/MyDocuments/BookProject/Book.java

File inputFile = new File("people.txt");
Scanner in = new Scanner(inputFile);