一、標(biāo)準(zhǔn)輸入輸出控制臺1. 標(biāo)準(zhǔn)輸出System.outSystem.out.print()/println()/printf()最常用的控制臺輸出。javaSystem.out.println(普通輸出); System.out.printf(格式化輸出%d %d %d%n, 3, 5, 3 5);2. 標(biāo)準(zhǔn)輸入System.inSystem.in是字節(jié)流InputStream通常用Scanner或BufferedReader包裝。方式一Scanner最常用javaimport java.util.Scanner; Scanner sc new Scanner(System.in); System.out.print(請輸入姓名); String name sc.nextLine(); System.out.print(請輸入年齡); int age sc.nextInt(); System.out.println(name 今年 age 歲); sc.close();方式二BufferedReader效率高需處理異常javaimport java.io.BufferedReader; import java.io.InputStreamReader; BufferedReader br new BufferedReader(new InputStreamReader(System.in)); System.out.print(請輸入內(nèi)容); String line br.readLine(); System.out.println(你輸入了 line); br.close();二、文件 I/O 基礎(chǔ)Java I/O 分為字節(jié)流和字符流頂層抽象類字節(jié)流InputStream/OutputStream字符流Reader/Writer1. 字節(jié)流讀寫文件適合圖片、視頻等二進制文件文件輸入流FileInputStreamjavaimport java.io.FileInputStream; import java.io.IOException; try (FileInputStream fis new FileInputStream(test.txt)) { int b; while ((b fis.read()) ! -1) { System.out.print((char) b); } } catch (IOException e) { e.printStackTrace(); }文件輸出流FileOutputStreamjavaimport java.io.FileOutputStream; import java.io.IOException; try (FileOutputStream fos new FileOutputStream(output.txt)) { String data Hello, Java I/O!; fos.write(data.getBytes()); } catch (IOException e) { e.printStackTrace(); }拷貝文件字節(jié)流一次讀取一個字節(jié)數(shù)組javatry (FileInputStream fis new FileInputStream(src.jpg); FileOutputStream fos new FileOutputStream(dst.jpg)) { byte[] buffer new byte[1024]; int len; while ((len fis.read(buffer)) ! -1) { fos.write(buffer, 0, len); } } catch (IOException e) { e.printStackTrace(); }2. 字符流讀寫文件適合文本文件FileReader / FileWriterjavaimport java.io.FileReader; import java.io.FileWriter; import java.io.IOException; // 寫文本文件 try (FileWriter fw new FileWriter(note.txt)) { fw.write(第一行內(nèi)容\n); fw.write(第二行內(nèi)容); } catch (IOException e) { e.printStackTrace(); } // 讀文本文件 try (FileReader fr new FileReader(note.txt)) { int ch; while ((ch fr.read()) ! -1) { System.out.print((char) ch); } } catch (IOException e) { e.printStackTrace(); }3. 緩沖流提高性能BufferedInputStream/BufferedOutputStream字節(jié)緩沖BufferedReader/BufferedWriter字符緩沖支持按行讀寫使用 BufferedReader 按行讀取javaimport java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; try (BufferedReader br new BufferedReader(new FileReader(data.txt))) { String line; while ((line br.readLine()) ! null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); }使用 BufferedWriter 按行寫入javaimport java.io.BufferedWriter; import java.io.FileWriter; import java.io.IOException; try (BufferedWriter bw new BufferedWriter(new FileWriter(out.txt))) { bw.write(第一行); bw.newLine(); bw.write(第二行); } catch (IOException e) { e.printStackTrace(); }三、轉(zhuǎn)換流字節(jié) ? 字符InputStreamReader字節(jié)→字符OutputStreamWriter字符→字節(jié)通常用于指定編碼如 UTF-8, GBK。javaimport java.io.*; // 以 UTF-8 編碼讀取文件 try (BufferedReader br new BufferedReader( new InputStreamReader(new FileInputStream(utf8.txt), UTF-8))) { String line; while ((line br.readLine()) ! null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); } // 以 GBK 編碼寫入文件 try (BufferedWriter bw new BufferedWriter( new OutputStreamWriter(new FileOutputStream(gbk.txt), GBK))) { bw.write(中文內(nèi)容); } catch (IOException e) { e.printStackTrace(); }四、NIONew I/OJava 1.4NIO 提供更高效的非阻塞 I/O核心ChannelBufferSelector。簡單示例使用 FileChannel 拷貝文件javaimport java.io.*; import java.nio.channels.FileChannel; try (FileChannel src new FileInputStream(src.txt).getChannel(); FileChannel dest new FileOutputStream(dest.txt).getChannel()) { dest.transferFrom(src, 0, src.size()); } catch (IOException e) { e.printStackTrace(); }使用 Files 工具類Java 7最簡潔javaimport java.nio.file.*; // 一次性讀取所有行 ListString lines Files.readAllLines(Paths.get(data.txt), StandardCharsets.UTF_8); lines.forEach(System.out::println); // 一次性寫入 ListString content Arrays.asList(行1, 行2, 行3); Files.write(Paths.get(out.txt), content, StandardCharsets.UTF_8); // 復(fù)制文件 Files.copy(Paths.get(a.txt), Paths.get(b.txt), StandardCopyOption.REPLACE_EXISTING);五、常見問題與最佳實踐問題建議中文亂碼使用InputStreamReader/OutputStreamWriter指定編碼如UTF-8忘記關(guān)閉流使用try-with-resourcesJava 7自動關(guān)閉效率低使用緩沖流BufferedReader/BufferedWriter大文件讀取使用BufferedReader按行讀或 NIO 的Files.lines()需要隨機訪問使用RandomAccessFile或 NIO 的FileChannel六、完整綜合示例含異常處理javaimport java.io.*; import java.nio.charset.StandardCharsets; import java.nio.file.*; public class IODemo { public static void main(String[] args) { // 寫入 try (BufferedWriter bw Files.newBufferedWriter(Paths.get(demo.txt), StandardCharsets.UTF_8)) { bw.write(Hello, 你好); bw.newLine(); bw.write(第二行); } catch (IOException e) { e.printStackTrace(); } // 讀取 try (BufferedReader br Files.newBufferedReader(Paths.get(demo.txt), StandardCharsets.UTF_8)) { String line; while ((line br.readLine()) ! null) { System.out.println(line); } } catch (IOException e) { e.printStackTrace(); } } }