Thinking in Java笔记9

深藏阁楼爱情的钟 2022-09-29 13:53 181阅读 0赞

（第10章笔记）

package com; import java.io.\*; import java.util.Arrays; class DirFilter implements FilenameFilter\{ String afn; //需要查找的文件名的关键字 DirFilter(String afn) \{this.afn = afn;\} public boolean accept(File dir, String name)\{ String f = new File(name).getName(); return f.indexOf(afn) != -1; \} \} public class Test9 \{ //可以将上面的类写成一个匿名内部类 public static FilenameFilter filter(final String afn)\{ //afn必须为final return new FilenameFilter()\{ String fn = afn; public boolean accept(File dir, String name)\{ String f = new File(name).getName(); return f.indexOf(fn)!=-1; \} \}; \} private final static String usage = "Usage: MakeDirectories path1 ... /n" + "Creates each path/n" + "Usage: MakeDirectories -d path1 ... /n" + "Deletes each path/n" + "Usage: MakeDirectories -r path1 path2 /n" + "Renames from path1 to path2/n"; private static void usage()\{ System.err.println(usage); System.exit(1); \} private static void fileData(File f)\{ System.out.println("Absolute path: " + f.getAbsolutePath() + "/n Can read: " + f.canRead() + "/n Can Write: " + f.canWrite() + "/n getName: " + f.getName() + "/n getParent: " + f.getParent() + "/n getPath: " + f.getPath() + "/n length: " + f.length() + "/n lastModified: " + f.lastModified()); if(f.isFile()) System.out.println("It's a file"); else if(f.isDirectory()) System.out.println("It's a directory"); \} //快捷文件处理 public class InFile extends DataInputStream\{ public InFile(String filename) throws FileNotFoundException\{ super(new BufferedInputStream(new FileInputStream(filename))); \} public InFile(File file) throws FileNotFoundException\{ this(file.getPath()); \} \} public class PrintFile extends PrintStream\{ public PrintFile(String filename)throws IOException\{ super(new BufferedOutputStream(new FileOutputStream(filename))); \} public PrintFile(File file)throws IOException\{ this(file.getPath()); \} \} public class OutFile extends DataOutputStream\{ public OutFile(String filename) throws IOException\{ super(new BufferedOutputStream(new FileOutputStream(filename))); \} public OutFile(File file)throws IOException\{ this(file.getPath()); \} \} public static void main(String\[\] args) \{ File path = new File("."); String\[\] list; if(args.length == 0) list = path.list(); else\{ //list方法会为目录对象中的每个文件名调用FilenameFilter对象的accept() //方法，核实哪个应包含在内。list()参数类型为FilenameFilter // list = path.list(new DirFilter(args\[0\])); list = path.list(filter(args\[0\])); \} for(int i = 0; i < list.length; i++) System.out.println(list\[i\]); //对list排序 Arrays.sort(list); for(int i = 0; i < list.length; i++) System.out.println(list\[i\]); System.out.println("-------------华丽丽的分割线-------------/n"); String temp = ""; //此处写上命令，如：abc，-d abc， -r abc abcd String\[\] arg = temp.split(" "); //将一个String以空格分开成数组 if(arg.length < 1) usage(); if(arg\[0\].equals("-r"))\{ if(arg.length != 3) usage(); File old = new File(arg\[1\]), rname = new File(arg\[2\]); old.renameTo(rname); fileData(old); fileData(rname); return ; \} int count = 0; boolean del = false; if(arg\[0\].equals("-d"))\{ count ++; del = true; \} for(; count < arg.length; count++)\{ File f = new File(arg\[count\]); if(f.exists())\{ System.out.println(f + " exists"); if(del)\{ System.out.println("deleting ..." + f); f.delete(); \} \} else\{ if(!del)\{ f.mkdirs(); System.out.println("created " + f); \} \} fileData(f); \} String file = "D://Eclipse//workspace//test//src//net//Ext\_test4.java"; //下面展示典型的旧版（Java 1.0）IO流的应用 try\{ //1. Buffered input file 缓冲的输入文件 //为了打开文件一边输入，需要使用FileInputStream，同时将一个String或者File对象作为文件名使用 //为了提高速度，对文件进行缓冲，从而获得用于一个BufferedInputStream的构建器结果句柄 //为了格式化形式读取输入数据，将结果句柄赋给DataInputStream的构建器 DataInputStream in = new DataInputStream(new BufferedInputStream(new FileInputStream(file))); String s, s2 = new String(); while((s = in.readLine()) != null) s2 += s + "/n"; in.close(); //2. Input from memory 从内存输入 StringBufferInputStream in2 = new StringBufferInputStream(s2); //字符缓冲输入流 int c; while((c = in2.read()) != -1) System.out.print((char)c); //3. Formatted memory input 格式化内存输入 try\{ DataInputStream in3 = new DataInputStream(new StringBufferInputStream(s2)); while(true) System.out.print((char)in3.readByte()); \}catch(EOFException e)\{ System.out.println("End of stream encountered"); \} //4. Line numbering & file output 行编号与文件输出 try\{ LineNumberInputStream li = new LineNumberInputStream(new StringBufferInputStream(s2)); DataInputStream in4 = new DataInputStream(li); PrintStream out1 = new PrintStream(new BufferedOutputStream(new FileOutputStream("IODemo.out"))); while((s = in4.readLine()) != null) out1.println("Line " + li.getLineNumber() + s); out1.close(); //如果不调用，当回过头来再次读取时，缓冲区就不会得到刷新，造成不完整 \}catch(EOFException e)\{ System.out.println("End of stream encountered"); \} //5. Storing & recovering data 保存与恢复数据 try\{ DataOutputStream out2 = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("Data.txt"))); out2.writeBytes("Here's the value of pi: /n"); out2.writeDouble(3.14159); out2.close(); DataInputStream in5 = new DataInputStream(new BufferedInputStream(new FileInputStream("Data.txt"))); System.out.println(in5.readLine()); System.out.println(in5.readDouble()); //必须知道数据项在流中的准确位置 \}catch(EOFException e)\{ System.out.println("End of stream encountered"); \} //6. Reading/writing random access files RandomAccessFile rf = new RandomAccessFile("rtest.dat", "rw"); for(int i = 0; i < 10; i++) rf.writeDouble(i\*1.414); rf.close(); rf = new RandomAccessFile("rtest.dat", "rw"); rf.seek(4\*8); rf.writeDouble(47.0001); rf.close(); rf = new RandomAccessFile("rtest.dat", "rw"); for(int i = 0; i < 10; i++) System.out.println("Value " + i + ": " + rf.readDouble()); rf.close(); \}catch(FileNotFoundException e)\{ System.out.println("File Not Found: " + file); \}catch(IOException e)\{ System.out.println("IO Exception"); \} //下面展示新版（Java 1.1）IO流的应用 try\{ //1. Reading input by lines: BufferedReader in = new BufferedReader(new FileReader(file)); String s, s2 = new String(); while((s = in.readLine())!=null) s2 += s + "/n"; in.close(); //2. Input from memory StringReader in2 = new StringReader(s2); int c; while((c = in2.read()) != -1) System.out.println((char)c); //3. Formatted memory input try\{ DataInputStream in3 = new DataInputStream(new StringBufferInputStream(s2)); while(true) System.out.print((char)in3.readByte()); \}catch(EOFException e)\{ System.out.println("End of stream"); \} //4. Line numbering & file output try\{ LineNumberReader li = new LineNumberReader(new StringReader(s2)); BufferedReader in4 = new BufferedReader(li); PrintWriter out1 = new PrintWriter(new BufferedWriter(new FileWriter("IODemo2.out"))); while((s = in4.readLine()) != null) out1.println("line " + li.getLineNumber() + s); out1.close(); \}catch(EOFException e)\{ System.out.println("End of stream"); \} //5. Storing & recovering data try\{ DataOutputStream out2 = new DataOutputStream(new BufferedOutputStream(new FileOutputStream("Data2.txt"))); out2.writeDouble(3.14159); out2.writeBytes("That was pi"); out2.close(); DataInputStream in5 = new DataInputStream(new BufferedInputStream(new FileInputStream("Data2.txt"))); BufferedReader in5br = new BufferedReader( new InputStreamReader(in5)); // Must use DataInputStream for data: System.out.println(in5.readDouble()); // Can now use the "proper" readLine(): System.out.println(in5br.readLine()); \} catch(EOFException e) \{ System.out.println("End of stream"); \} \}catch(FileNotFoundException e) \{ System.out.println("File Not Found:" + file); \}catch(IOException e)\{ System.out.println("IO Exception"); \} //从标准输入中读取数据 //Java 提供了相应的System.in，System.out 以及System.err。贯这一整本书，大家都会接触到如何用 //System.out进行标准输出，它已预封装成一个PrintStream对象。System.err 同样是一个PrintStream， //但System.in是一个原始的InputStream，未进行任何封装处理。这意味着尽管能直接使用System.out //和System.err，但必须事先封装System.in，否则不能从中读取数据 DataInputStream in6 = new DataInputStream(new BufferedInputStream(System.in)); String s6; try \{ while((s6 = in6.readLine())!=null) System.out.println(s6); // An empty line terminates the program \} catch(IOException e) \{ e.printStackTrace(); \} \} \}

运行结果：

略。

package com; import java.io.\*; import java.util.\*; import java.util.zip.GZIPInputStream; import java.util.zip.GZIPOutputStream; class Counter\{ private int i = 1; int read() \{ return i; \} void increment() \{ i++; \} \} public class Test9\_2 \{ //class SortedWordCount private FileInputStream file; private StreamTokenizer st; private Hashtable counts = new Hashtable(); Test9\_2(String filename) throws FileNotFoundException\{ try\{ file = new FileInputStream(filename); st = new StreamTokenizer(file); st.ordinaryChar('.'); //指出该字符没有特别重要的意义 st.ordinaryChar('-'); //如果不加，abc.a和a-dd之类的就会被当做一个单词 \}catch(FileNotFoundException e)\{ System.out.println("Could not open " + filename); throw e; \} \} void cleanup()\{ try\{ file.close(); \}catch(IOException e)\{ System.out.println("file.close() is unsuccessfull"); \} \} void countWord()\{ try\{ while(st.nextToken() != StreamTokenizer.TT\_EOF)\{ String s; switch(st.ttype)\{ case StreamTokenizer.TT\_EOL: //行尾 s = new String("EOL"); break; case StreamTokenizer.TT\_NUMBER: //数字 s = Double.toString(st.nval); break; case StreamTokenizer.TT\_WORD: //字串 s = st.sval; break; default: //字符 s = String.valueOf((char)st.ttype); \} if(counts.containsKey(s)) ((Counter)counts.get(s)).increment(); else counts.put(s, new Counter()); \} \}catch(IOException e)\{ System.out.println("st.nextToken() unsuccessful"); \} \} Enumeration values()\{ return counts.elements(); \} Enumeration keys()\{ return counts.keys(); \} Counter getCounter(String s)\{ return (Counter)counts.get(s); \} Enumeration sortedKeys()\{ Enumeration e = counts.keys(); SortVector sv = new SortVector(new Test7\_2.StringCompare()); while(e.hasMoreElements()) sv.addElement(e.nextElement()); sv.sort(); return sv.elements(); \} public static void main(String\[\] args) \{ String filename = "C://Users//zhb//Desktop//Echo.java"; try\{ Test9\_2 wc = new Test9\_2(filename); wc.countWord(); Enumeration keys = wc.sortedKeys(); while(keys.hasMoreElements())\{ String key = (String)keys.nextElement(); System.out.println(key + ": " + wc.getCounter(key).read()); \} wc.cleanup(); \}catch(Exception e)\{ e.printStackTrace(); \} //重定向System.in, System.out, System.err try \{ BufferedInputStream in = new BufferedInputStream( new FileInputStream("Redirecting.java")); // Produces deprecation message: PrintStream out = new PrintStream( new BufferedOutputStream( new FileOutputStream("test.out"))); System.setIn(in); System.setOut(out); System.setErr(out); BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); String s; while((s = br.readLine()) != null) System.out.println(s); out.close(); // Remember this! \} catch(IOException e) \{ e.printStackTrace(); \} //用GZIP进行单文件的简单压缩 try \{ BufferedReader in = new BufferedReader( new FileReader("test.out")); BufferedOutputStream out = new BufferedOutputStream( new GZIPOutputStream( new FileOutputStream("test.gz"))); System.out.println("Writing file"); int c; while((c = in.read()) != -1) out.write(c); in.close(); out.close(); System.out.println("Reading file"); BufferedReader in2 = new BufferedReader( new InputStreamReader( new GZIPInputStream( new FileInputStream("test.gz")))); String s; while((s = in2.readLine()) != null) System.out.println(s); \} catch(Exception e) \{ e.printStackTrace(); \} \} \}

运行结果：

略。

package com; import java.io.\*; //介绍Serializable class Data implements Serializable\{ private int i; Data(int x) \{ i = x; \} public String toString()\{ return Integer.toString(i); \} \} public class Test9\_3 implements Serializable\{ //class Worm private static int r()\{ return (int)(Math.random()\*10); \} private Data\[\] d = \{ new Data(r()), new Data(r()), new Data(r()) \}; private Test9\_3 next; private char c; // private transient char c; 如果不希望敏感信息（如密码）被自动序列化传输，可以用transient关键字 Test9\_3(int i, char x)\{ System.out.println("Test9\_3(Worm) constructor: " + i); c = x; if(--i > 0) next = new Test9\_3(i, (char)(x + 1)); \} Test9\_3()\{ System.out.println("Default constructor"); \} public String toString()\{ String s = ":" + c + "("; for(int i = 0; i < d.length; i++) s += d\[i\].toString(); s += ")"; if(next != null) s += next.toString(); return s; \} public static void main(String\[\] args) \{ Test9\_3 w = new Test9\_3(6, 'a'); System.out.println("w = " + w); //一下两例演示如何序列化一个对象，并重新装配，第一个是读写文件，第二个是读写一个ByteArray //回复一个序列化的对象后，如果想做更多的事，必须保证JVM能在本地类路径或者因特网的其他地方找到相关的.class文件 //如果把这个文件package到net目录下，并且恢复对象是将路径改成c://，则JVM找不到相应的.class文件，会出现一个 //ClassNotFoundException的违例 try\{ ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("worm.out")); out.writeObject("Worm storage"); out.writeObject(w); out.close(); ObjectInputStream in = new ObjectInputStream(new FileInputStream("worm.out")); String s = (String)in.readObject(); Test9\_3 w2 = (Test9\_3)in.readObject(); System.out.println(s + ", w2 = " + w2); \}catch(Exception e)\{ e.printStackTrace(); \} try\{ ByteArrayOutputStream bout = new ByteArrayOutputStream(); ObjectOutputStream out = new ObjectOutputStream(bout); out.writeObject("Worm Storage"); out.writeObject(w); out.flush(); ObjectInputStream in = new ObjectInputStream(new ByteArrayInputStream(bout.toByteArray())); String s2 = (String)in.readObject(); Test9\_3 w3 = (Test9\_3)in.readObject(); System.out.println(s2 + ", w3 = " + w3); \}catch(Exception e)\{ e.printStackTrace(); \} \} \}

运行结果：

Test9\_3(Worm) constructor: 6  
Test9\_3(Worm) constructor: 5  
Test9\_3(Worm) constructor: 4  
Test9\_3(Worm) constructor: 3  
Test9\_3(Worm) constructor: 2  
Test9\_3(Worm) constructor: 1  
w = :a(484):b(425):c(277):d(269):e(182):f(844)  
Worm storage, w2 = :a(484):b(425):c(277):d(269):e(182):f(844)  
Worm Storage, w3 = :a(484):b(425):c(277):d(269):e(182):f(844)

package com; import java.io.\*; import java.util.\*; //介绍Externalizable class Blip implements Externalizable\{ private int i; private String s; //恢复一个Externalizable会调用构造器，所以构造器必须为public，否则会产生一个违例 //Serializable则不存在这样的问题，因为它是将对象以二进制位为基础恢复 public Blip()\{ System.out.println("Blip Constructor"); \} public Blip(String x, int a)\{ System.out.println("Blip(Stirng x, int a)"); i = a; s = x; \} public String toString()\{ return s + i; \} //序列化和重新装配时会自动调用下面两个方法，方便用户进行控制哪些要序列化哪些不要 public void writeExternal(ObjectOutput out) throws IOException\{ System.out.println("Blip.writeExternal"); out.writeObject(s); out.writeInt(i); \} public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException\{ System.out.println("Blip.readExternal"); s = (String)in.readObject(); i = in.readInt(); \} \} public class Test9\_4 \{ public static void main(String\[\] args) \{ System.out.println("Constructor objects:"); Blip b = new Blip("A String ", 47); System.out.println(b.toString()); try\{ ObjectOutputStream o = new ObjectOutputStream(new FileOutputStream("Blip.out")); System.out.println("Saving object:"); o.writeObject(b); o.close(); ObjectInputStream in = new ObjectInputStream(new FileInputStream("Blip.out")); System.out.println("Recovering b:"); b = (Blip)in.readObject(); System.out.println(b.toString()); \}catch(Exception e)\{ e.printStackTrace(); \} \} \} /\* Externalizable有其替代方法： \* 我们可以实现Serializable接口，并添加名为writeObject()和readObject()的方法，一旦对象被序列化 \* 或者重新装配，就会分别调用这两个方法。也就是说，只要提供了这两个方法，就会优先使用它们，而不用 \* 考虑默认的序列化机制。但这两个方法必须有下列准确的签名： \* private void writeObject(ObjectOutputStream stream) throws IOException; \* private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException; \*/

运行结果：

Constructor objects:  
Blip(Stirng x, int a)  
A String 47  
Saving object:  
Blip.writeExternal  
Recovering b:  
Blip Constructor  
Blip.readExternal  
A String 47