Javaの例外処理で知らないと損する7つのテクニック：【改訂版】Eclipseではじめるプログラミング（24）（3/3 ページ）

//略
void exec() throws Exception {
//略
    } finally {
        in.close();
        out.close();
    }
}

package sample24;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
  
public class SampleApp3 {
    public void execute() throws java.io.IOException {
        java.util.List lines = new java.util.LinkedList();
        BufferedReader in = null;
        try {
            in = new BufferedReader(new FileReader("src/sample24/SampleApp.java"));
            String line = null;
            while ((line = in.readLine()) != null) {
                lines.add(line);
            }
        } finally {
            if (in != null) {
                in.close();  // inはここで確実にclose
            }
        }
        BufferedWriter out = null;
        try {
            out = new BufferedWriter(new FileWriter("src/sample24/SampleApp.txt"));
            for (String line : lines) {
                out.write(line);
                out.newLine();
            }
            out.flush();
        } finally {
            if (out != null) {
                out.close();  // outはここで確実にclose
            }
        }
    }
    public static void main(String[] args) {
        SampleApp3 app = new SampleApp3();
        try {
            app.execute();
        } catch (java.io.IOException e) {
            e.printStackTrace(); // 読み込みか書き込みでエラー
        }
    }
}

package sample24;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
  
public class SampleApp4 {
    public void execute() throws java.io.IOException {
        BufferedReader in = null;
        try {
            in = new BufferedReader(new FileReader("src/sample24/SampleApp.java"));
            BufferedWriter out = null;
            try {
                out = new BufferedWriter(new FileWriter("src/sample24/SampleApp.txt"));
                String line;
                while ((line = in.readLine()) != null) {
                    out.write(line);
                    out.newLine();
                    out.flush();
                }
            } catch (java.io.IOException e) {
                // エラーが発生する場所は複数ある
                // new FileWriter()
                // new BufferedWriter() 
                // in.readLine()
                // out.write(), out.newLine(), out.flush()
                e.printStackTrace();
            } finally {
                if (out != null) {
                    out.close(); // outはここで確実にclose
                }
            }
        } catch (java.io.IOException e) {
            // new FileReader, new BufferedReader でエラー か
            // out.close() でエラー
            e.printStackTrace();
        } finally {
            if (in != null) {
                in.close(); // inはここで確実にclose
            }
        }
    }
    public static void main(String[] args) {
        SampleApp4 app = new SampleApp4();
        try {
            app.execute();
        } catch (java.io.IOException e) {
            e.printStackTrace(); // in.close()でエラー
        }
    }
}