File file = new File(file_name);
FileReader filereader = new FileReader(file);

try{
  File file = new File("c:\\tmp\\test.txt");
  FileReader filereader = new FileReader(file);
}catch(FileNotFoundException e){
  System.out.println(e);
}

テキストを読む

read
public int read() throws IOException

try{
  File file = new File("c:\\tmp\\test.txt");
  FileReader filereader = new FileReader(file);

  int ch = filereader.read();
  System.out.println((char)ch);
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

ファイルの最後まで読み込む

try{
  File file = new File("c:\\tmp\\test.txt");
  FileReader filereader = new FileReader(file);

  int ch = filereader.read();
  while(ch != -1){
    System.out.print((char)ch);

    ch = filereader.read();
  }
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

try{
  File file = new File("c:\\tmp\\test.txt");
  FileReader filereader = new FileReader(file);

  int ch;
  while((ch = filereader.read()) != -1){
    System.out.print((char)ch);
  }
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

ファイルを閉じる

close
public void close() throws IOException

try{
  File file = new File("c:\\tmp\\test.txt");
  FileReader filereader = new FileReader(file);

  int ch;
  while((ch = filereader.read()) != -1){
    System.out.print((char)ch);
  }

  filereader.close();
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

サンプルプログラム

import java.io.File;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;

class streamTest1{
  public static void main(String args[]){
    try{
      File file = new File("./tmp/test.txt");
      FileReader filereader = new FileReader(file);

      int ch;
      while((ch = filereader.read()) != -1){
        System.out.print((char)ch);
      }

      filereader.close();
    }catch(FileNotFoundException e){
      System.out.println(e);
    }catch(IOException e){
      System.out.println(e);
    }
  }
}

[xxxxxxxx@dddddddddd Stream]$ javac streamTest1.java
[xxxxxxxx@dddddddddd Stream]$ java streamTest1
abcdef
日本語
[xxxxxxxx@dddddddddd Stream]$ 

private boolean checkBeforeReadfile(File file){
  if (file.exists()){
    if (file.isFile() && file.canRead()){
      return true;
    }
  }

  return false;
}

サンプルプログラム

import java.io.File;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;

class streamTest2{
  public static void main(String args[]){
    try{
      File file = new File("./tmp/test.txt");
//      File file = new File( args[0] );

      if (checkBeforeReadfile(file)){
        FileReader filereader = new FileReader(file);

        int ch;
        while((ch = filereader.read()) != -1){
          System.out.print((char)ch);
        }

        filereader.close();
      }else{
        System.out.println("ファイルが見つからないか開けません");
      }
    }catch(FileNotFoundException e){
      System.out.println(e);
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeReadfile(File file){
    if (file.exists()){
      if (file.isFile() && file.canRead()){
        return true;
      }
    }

    return false;
  }
}

[xxxxxxxx@dddddddddd Stream]$ java streamTest1
abcdef
日本語
[xxxxxxxx@dddddddddd Stream]$ 

File file = new File(file_name);
FileReader filereader = new FileReader(file);
BufferedReader br = new BufferedReader(filereader);

File file = new File(file_name);
BufferedReader br = new BufferedReader(new FileReader(file));

テキストを1行単位で読む

readLine
public String readLine() throws IOException

try{
  File file = new File("c:\\tmp\\test.txt");
  BufferedReader br = new BufferedReader(new FileReader(file));

  String str = br.readLine();
  while(str != null){
    System.out.println(str);

    str = br.readLine();
  }

  br.close();
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

try{
  File file = new File("c:\\tmp\\test.txt");
  BufferedReader br = new BufferedReader(new FileReader(file));

  String str;
  while((str = br.readLine()) != null){
    System.out.println(str);
  }

  br.close();
}catch(FileNotFoundException e){
  System.out.println(e);
}catch(IOException e){
  System.out.println(e);
}

ファイルを閉じる

close
public void close() throws IOException

サンプルプログラム

import java.io.File;
import java.io.FileReader;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.IOException;

class streamTest3{
  public static void main(String args[]){
    try{
      File file = new File("./tmp/test.txt");
//      File file = new File( args[0] );

      if (checkBeforeReadfile(file)){
        BufferedReader br = new BufferedReader(new FileReader(file));

        String str;
        while((str = br.readLine()) != null){
          System.out.println(str);
        }

        br.close();
      }else{
        System.out.println("ファイルが見つからないか開けません");
      }
    }catch(FileNotFoundException e){
      System.out.println(e);
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeReadfile(File file){
    if (file.exists()){
      if (file.isFile() && file.canRead()){
        return true;
      }
    }

    return false;
  }
}

[xxxxxxxx@dddddddddd Stream]$ java streamTest1
abcdef
日本語
[xxxxxxxx@dddddddddd Stream]$ 

File file = new File(file_name);
FileWriter filewriter = new FileWriter(file);

try{
  File file = new File("c:\\tmp\\test.txt");
  FileWriter filewriter = new FileWriter(file);
}catch(IOException e){
  System.out.println(e);
}

ファイルへの書き込み

write
public void write(String str) throws IOException

try{
  File file = new File("c:\\tmp\\test.txt");
  FileWriter filewriter = new FileWriter(file);

  filewriter.write("こんにちは");
}catch(IOException e){
  System.out.println(e);
}

ファイルを閉じる

close
public void close() throws IOException

try{
  File file = new File("c:\\tmp\\test.txt");
  FileWriter filewriter = new FileWriter(file);

  filewriter.write("こんにちは");

  filewriter.close();
}catch(IOException e){
  System.out.println(e);
}

サンプルプログラム

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

class streamTest4{
  public static void main(String args[]){
    try{
      File file = new File("./tmp/test01.txt");
//      File file = new File( args[0] );

      if (checkBeforeWritefile(file)){
        FileWriter filewriter = new FileWriter(file);

        filewriter.write("こんにちは\r\n");
        filewriter.write("お元気ですか\r\n");

        filewriter.close();
      }else{
        System.out.println("ファイルに書き込めません");
      }
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeWritefile(File file){
    if (file.exists()){
      if (file.isFile() && file.canWrite()){
        return true;
      }
    }

    return false;
  }
}

[xxxxxxxx@dddddddddd Stream]$ java streamTest4
ファイルに書き込めません
[xxxxxxxx@dddddddddd Stream]$ 

[wwwadmin@kamifuji18 Stream]$ touch tmp/test01.txt
[wwwadmin@kamifuji18 Stream]$ ll tmp
合計 4
-rw-r--r-- 1 wwwadmin wwwadmin 17  1月 31 12:05 test.txt
-rw-r--r-- 1 wwwadmin wwwadmin  0  1月 31 13:21 test01.txt
[xxxxxxxx@dddddddddd Stream]$ 

[xxxxxxxx@dddddddddd Stream]$ java streamTest4
[xxxxxxxx@dddddddddd Stream]$ 

[xxxxxxxx@dddddddddd Stream]$ cat tmp/test01.txt
こんにちは
お元気ですか
[xxxxxxxx@dddddddddd Stream]$ 

File file = new File(file_name);
FileWriter filewriter = new FileWriter(file, true);

サンプルプログラム

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

class streamTest5{
  public static void main(String args[]){
    try{
      File file = new File("./tmp/test01.txt");
//      File file = new File( args[0] );

      if (checkBeforeWritefile(file)){
        FileWriter filewriter = new FileWriter(file, true);

        filewriter.write("はい。元気です\r\n");
        filewriter.write("ではまた\r\n");

        filewriter.close();
      }else{
        System.out.println("ファイルに書き込めません");
      }
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeWritefile(File file){
    if (file.exists()){
      if (file.isFile() && file.canWrite()){
        return true;
      }
    }

    return false;
  }
}

[xxxxxxxx@dddddddddd Stream]$ cat tmp/test01.txt
こんにちは
お元気ですか
[xxxxxxxx@dddddddddd Stream]$ 

[xxxxxxxx@dddddddddd Stream]$ javac streamTest5.java
[xxxxxxxx@dddddddddd Stream]$ java streamTest5
[xxxxxxxx@dddddddddd Stream]$ cat tmp/test01.txt
こんにちは
お元気ですか
はい。元気です
ではまた
[xxxxxxxx@dddddddddd Stream]$

File file = new File(file_name);
FileWriter filewriter = new FileWriter(file);
BufferedWriter bw = new BufferedWriter(filewriter);

File file = new File(file_name);
BufferedWriter bw = new BufferedWriter(new FileWriter(file));

自動で判別された改行文字の出力

newLine
public void newLine() throws IOException

File file = new File(file_name);
BufferedWriter bw = new BufferedWriter(new FileWriter(file));
bw.write("こんにちは");
bw.newLine();

ファイルを閉じる

close
public void close() throws IOException

サンプルプログラム

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

class streamTest6{
  public static void main(String args[]){
    try{
      File file = new File( "./tmp/test02.txt );
//      File file = new File( args[0] );

      if (checkBeforeWritefile(file)){
        BufferedWriter bw = new BufferedWriter(new FileWriter(file));

        bw.write("こんにちは");
        bw.newLine();
        bw.write("お元気ですか？");
        bw.newLine();

        bw.close();
      }else{
        System.out.println("ファイルに書き込めません");
      }
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeWritefile(File file){
    if (file.exists()){
      if (file.isFile() && file.canWrite()){
        return true;
      }
    }

    return false;
  }
}

[wwwadmin@kamifuji18 Stream]$ touch ./tmp/test02.txt
[wwwadmin@kamifuji18 Stream]$ java streamTest6
[wwwadmin@kamifuji18 Stream]$ cat ./tmp/test02.txt
こんにちは
お元気ですか？
[wwwadmin@kamifuji18 Stream]$

File file = new File(file_name);
FileWriter filewriter = new FileWriter(file);
BufferedWriter bw = new BufferedWriter(filewriter);
PrintWriter pw = new PrintWriter(bw);

File file = new File(file_name);
PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(file)));

File file = new File(file_name);
PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(file)));

pw.println("文字列");
pw.println(10);

println
public void println(String x)

ファイルを閉じる

close
public void close()

サンプルプログラム

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

class streamTest7{
  public static void main(String args[]){
    try{
      File file = new File( "./tmp/test03.txt" );
//      File file = new File( args[0] );

      if (checkBeforeWritefile(file)){
        PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter(file)));

        pw.println("今日の最高気温は");
        pw.println(10);
        pw.println("度です");

        pw.close();
      }else{
        System.out.println("ファイルに書き込めません");
      }
    }catch(IOException e){
      System.out.println(e);
    }
  }

  private static boolean checkBeforeWritefile(File file){
    if (file.exists()){
      if (file.isFile() && file.canWrite()){
        return true;
      }
    }

    return false;
  }
}

[xxxxxxxx@dddddddddd Stream]$ touch ./tmp/test03.txt
[xxxxxxxx@dddddddddd Stream]$ java streamTest7
[xxxxxxxx@dddddddddd Stream]$ cat ./tmp/test03.txt
今日の最高気温は
10
度です
[xxxxxxxx@dddddddddd Stream]$