16.3. Reading: FileReader and BufferedReader

In Java, you can read the contents of a file in multiple ways:

Using a FileReader object (since Java 1.1)
Using a BufferedReader object (since Java 1.1)
Using a Scanner object (since Java 1.5)
Using the Files class (since Java 1.7)

Let us see how to use these alternative methods to read names from a file, as in the following example.

Rick
Morty
Birdperson
Beth
Summer
Jerry
Mr. Meeseeks
Gearhead

Reading character by character with a `FileReader`

public class ReadFromFileUsingFileReader {
  // Reads a file, character by character, using a FileReader.
  public static void main(String[] args) {
    File file = new File("src/main/resources/names.txt");
    List<String> names = new ArrayList<>();

    try (FileReader reader = new FileReader(file)) {
      String name = "";

      while (reader.ready()) {
        char character = (char) reader.read();

        if (character == '\n') {
          names.add(name);
          name = "";
        } else {
          name += character;
        }
      }
    } catch (IOException e) {
      e.printStackTrace();
    }

    System.out.println(names);
  }
}

[Rick, Morty, Birdperson, Beth, Summer, Jerry, Mr. Meeseeks]

Note that this code used the try-with-resources block. If we had not, we would need to close the FileReader after opening it, as in the following example.

package reading.file_reader;

import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class ReadFromFileUsingFileReaderWithoutTryWithResources {

  public static void main(String[] args) {
    File file = new File("src/main/resources/names.txt");
    List<String> names = new ArrayList<>();

    FileReader reader = null;
    try {
      reader = new FileReader(file);
      String name = "";

      while (reader.ready()) {
        char character = (char) reader.read();

        if (character == '\n') {
          names.add(name);
          name = "";
        } else {
          name += character;
        }
      }
    } catch (IOException e) {
      e.printStackTrace();
    } finally {
      if (reader != null) {
        try {
          reader.close();
        } catch (IOException e) {
          e.printStackTrace();
        }
      }
    }

    System.out.println(names);
  }
}

Using a BufferedReader: Reading line by line

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class ReadFromFileUsingBufferedReader {
  // Reads a file, line by line, using a BufferedReader. Loops using readLine()
  public static void main(String[] args) {
    File file = new File("src/main/resources/names.txt");
    List<String> names = new ArrayList<>();

    try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
      String line = reader.readLine();

      while (line != null) {
        names.add(line);
        line = reader.readLine();
      }

    } catch (IOException e) {
      e.printStackTrace();
    }

    System.out.println("Names: " + names);
  }
}

Names: [Rick, Morty, Birdperson, Beth, Summer, Jerry, Mr. Meeseeks, Gearhead]

Using a BufferedReader: Alternative looping condition

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class ReadFromFileUsingBufferedReaderReady {
  // Reads a file, line by line, using a BufferedReader. Loops using ready().
  public static void main(String[] args) {
    File file = new File("src/main/resources/names.txt");
    List<String> names = new ArrayList<>();

    try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
      while (reader.ready()) {
        String name = reader.readLine();
        names.add(name);
      }

    } catch (IOException e) {
      e.printStackTrace();
    }

    System.out.println("Names: " + names);
  }
}

Names: [Rick, Morty, Birdperson, Beth, Summer, Jerry, Mr. Meeseeks, Gearhead]

Using a BufferedReader and a Stream

import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.util.List;

public class ReadFromFileUsingBufferedReaderStream {
  // Reads a file, line by line, using a BufferedReader and the lines() method.
  public static void main(String[] args) {
    File file = new File("src/main/resources/names.txt");
    List<String> names = null;

    try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
      names = reader.lines()
                    .toList();
    } catch (IOException e) {
      e.printStackTrace();
    }

    System.out.println("Names: " + names);
  }
}

Names: [Rick, Morty, Birdperson, Beth, Summer, Jerry, Mr. Meeseeks, Gearhead]

Exercise 1

The athletes.data file contains data about athletes, as shown below.

RUNNER|name=Mary;age=43;id=47868;injured=false;shoes=Asics
RUNNER|age=18;name=John;id=47869;injured=true;shoes=Adidas
SWIMMER|id=47870;name=Mike;injured=false;modality=freestyle
RUNNER|name=Amy;age=23;id=47871;shoes=Nike;injured=false
SWIMMER|id=47872;name=Bill;modality=butterfly;injured=false
SWIMMER|id=47872;modality=backstroke;name=Ryan;injured=true

Write a program that uses a BufferedReader to read such a file and create objects out of its data. Create one Athlete per line of the type identified in the beginning of the line.

Use the classes available below.

Athlete.java
Runner.java
Swimmer.java
Main.java

public abstract class Athlete {
  String id;
  String name;
  int age;
  boolean injured;

  public Athlete() {
    id = null;
    name = null;
    age = 0;
    injured = false;
  }

  public Athlete(String id, String name, int age, boolean injured) {
    this.id = id;
    this.name = name;
    this.age = age;
    this.injured = injured;
  }


  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public String getId() {
    return id;
  }

  public void setId(String id) {
    this.id = id;
  }

  public int getAge() {
    return age;
  }

  public void setAge(int age) {
    this.age = age;
  }

  public boolean isInjured() {
    return injured;
  }

  public void setInjured(boolean injured) {
    this.injured = injured;
  }
}

public class Runner extends Athlete {
  String shoes;

  public Runner() {
    super();
    shoes = null;
  }

  public Runner(String id, String name, int age, boolean injured, String shoes) {
    super(id, name, age, injured);
    this.shoes = shoes;
  }

  public String getShoes() {
    return shoes;
  }

  public void setShoes(String shoes) {
    this.shoes = shoes;
  }

  @Override
  public String toString() {
    return "Runner {" +
            id +
            ", " + name +
            ", " + age +
            ", " + injured +
            ", " + shoes +
            "}";
  }

}

public class Swimmer extends Athlete {
  String modality;

  public Swimmer() {
    super();
    modality = null;
  }

  public Swimmer(String id, String name, int age, boolean injured, String modality) {
    super(id, name, age, injured);
    this.modality = modality;
  }

  public String getModality() {
    return modality;
  }

  public void setModality(String modality) {
    this.modality = modality;
  }
  
  @Override
  public String toString() {
    return "Swimmer {" +
            id +
            ", " + name +
            ", " + age +
            ", " + injured +
            ", " + modality +
            "}";
  }
}