File file = new File("abc.txt");if(!file.exists()){System.out.println(file.exists());file.createNewFile();}System.out.println(file.getAbsolutePath());

    File file = File.createTempFile("defaultTmp","tmpp",new File("./"));System.out.println(file.getAbsolutePath());--------------------------------------------------

/Users/liuxin/work/workspace2/learnJava/./defaultTmp5487876755372558069tmpp

File file = File.createTempFile("defaultTmp",".tmpp");System.out.println(file.getAbsolutePath());------------------------------------------------------------------------
/var/folders/f9/x95426d95ng7wgy7f7yccj3w0000gn/T/defaultTmp1175907986750188229tmpp

File file = File.createTempFile("defaultTmp",".tmpp");file.deleteOnExit();System.out.println(file.getAbsolutePath());

File testFile = new File("testFile");if(!testFile.exists()){testFile.mkdirs();}testFile.deleteOnExit();File file = File.createTempFile("defaultTmp","tmpp");System.out.println(file.getAbsolutePath());File file2 = File.createTempFile("defaultTmp2",".tmpp",testFile);System.out.println(file2.getAbsolutePath());File file3 = File.createTempFile("defaultTmp3",null,testFile);System.out.println(file3.getAbsolutePath());=======================================
/var/folders/f9/x95426d95ng7wgy7f7yccj3w0000gn/T/defaultTmp5296324826431648502tmpp
/Users/liuxin/work/workspace2/learnJava/testFile/defaultTmp21551336802243345058.tmpp
/Users/liuxin/work/workspace2/learnJava/testFile/defaultTmp33930717872920538957.tmp

File currentFile = new File(".");System.out.println(currentFile.getAbsolutePath());for(File file : currentFile.listFiles()){System.out.println(file.getName());}

File file = new File(".");
System.out.println(file.getAbsolutePath());
System.out.println(new File(file.getAbsolutePath()).getParent());-----------------------
/Users/liuxin/work/workspace2/learnJava/.
/Users/liuxin/work/workspace2/learnJavagetParent()只有在定义文件时有路径时才起作用.

public static void testFile() throws IOException{// 创建字节输入流FileInputStream fis = new FileInputStream("a.txt");// 创建一个长度为1024的“竹筒”byte[] bbuf = new byte[1024];// 用于保存实际读取的字节数int hasRead = 0;// 使用循环来重复“取水”过程while ((hasRead = fis.read(bbuf)) > 0 ){// 取出“竹筒”中水滴（字节），将字节数组转换成字符串输入！System.out.print(new String(bbuf , 0 , hasRead ));}// 关闭文件输入流，放在finally块里更安全
                    fis.close();}

File file = new File(".");String[] nameList = file.list((dir, name) -> name.endsWith(".java")|| new File(name).isDirectory());for(String name : nameList){System.out.println(name);}================================
.settings
a
bin
lib
result
sqlModify
src
testFile

public static void testFile2() throws IOException{// 创建字节输入流FileInputStream fis = new FileInputStream("a.txt");//读取一个字节,返回的是int,所以要用char强转System.out.println((char)fis.read());// 创建一个长度为1024的“竹筒”byte[] bbuf = new byte[1024];//读取5个字节,放在bbuf的index为10的位置fis.read(bbuf,10,10);
//                    从bbuf中index为10的位置读取5个字节构成字符串System.out.println(new String(bbuf , 10, 5));//转换成String后,byte[]不变System.out.println(new String(bbuf , 10, 5));// 用于保存实际读取的字节数int hasRead = 0;// 使用循环来重复“取水”过程while ((hasRead = fis.read(bbuf)) > 0 ){//重新赋值后,byte[]会改变System.out.println(new String(bbuf , 10, 5));// 取出“竹筒”中水滴（字节），将字节数组转换成字符串输入！System.out.println("==============================================");String test = new String(bbuf , 0 , hasRead );System.out.println(test);System.out.println("=================="+new String(bbuf , 0 , hasRead ).length()+"============================");}// 关闭文件输入流，放在finally块里更安全
                    fis.close();}

打印结果如下<
?xml
?xml
ncodi
==============================================
on="1.0" encoding="UTF-8"?>
<projectDescription><name>learnJava</name><comment></comment><projects></projects><buildSpec><buildCommand><name>org.eclipse.jdt.core.javabuilder</name><arguments></arguments></buildCommand></buildSpec><natures><nature>org.eclipse.jdt.core.javanature</nature></natures>
</projectDescription>我很好啊,看看需不要utf-8
==================373============================

public static void testFile3() {try(// 创建字符输入流FileReader fr = new FileReader("a.txt")){// 创建一个长度为32的“竹筒”char[] cbuf = new char[32];System.out.println(fr.read(cbuf,0,32));System.out.println(new String(cbuf));// 用于保存实际读取的字符数int hasRead = 0;// 使用循环来重复“取水”过程while ((hasRead = fr.read(cbuf)) > 0 ){// 取出“竹筒”中水滴（字符），将字符数组转换成字符串输入！
//                    System.out.print(new String(cbuf , 0 , hasRead));System.out.print(new String(cbuf));}}catch (IOException ex){ex.printStackTrace();}}

public static void testFileWriter() {　　　　//这里a.txt可以不存在，如果不存在回自动生成，但是没搞明白怎么设置编码格式try(FileWriter fw = new FileWriter("a.txt")){fw.write("锦瑟 - 李商隐\r\n");fw.write("锦瑟无端五十弦，一弦一柱思华年。\r\n");fw.write("庄生晓梦迷蝴蝶，望帝春心托杜鹃。\r\n");fw.write("沧海月明珠有泪，蓝田日暖玉生烟。\r\n");fw.write("此情可待成追忆，只是当时已惘然。\r\n");}catch (IOException ioe){ioe.printStackTrace();}}

public static void PrintStream() {try(FileOutputStream fos = new FileOutputStream("a.txt");PrintStream ps = new PrintStream(fos)){// 使用PrintStream执行输出ps.println("普通字符串");// 直接使用PrintStream输出对象ps.println(new LearnIO());}catch (IOException ioe){ioe.printStackTrace();}}

普通字符串
learnIO.LearnIO@677327b6

public static void stringNodeTest() {String src = "从明天起，做一个幸福的人\n"+ "喂马，劈柴，周游世界\n"+ "从明天起，关心粮食和蔬菜\n"+ "我有一所房子，面朝大海，春暖花开\n"+ "从明天起，和每一个亲人通信\n"+ "告诉他们我的幸福\n";char[] buffer = new char[32];int hasRead = 0;try(StringReader sr = new StringReader(src)){// 采用循环读取的访问读取字符串while((hasRead = sr.read(buffer)) > 0){System.out.print(new String(buffer ,0 , hasRead));}}catch (IOException ioe){ioe.printStackTrace();}try(// 创建StringWriter时，实际上以一个StringBuffer作为输出节点// 下面指定的20就是StringBuffer的初始长度StringWriter sw = new StringWriter()){// 调用StringWriter的方法执行输出sw.write("有一个美丽的新世界，\n");sw.write("她在远方等我,\n");sw.write("哪里有天真的孩子，\n");sw.write("还有姑娘的酒窝\n");System.out.println("----下面是sw的字符串节点里的内容----");// 使用toString()方法返回StringWriter的字符串节点的内容System.out.println(sw.toString());}catch (IOException ex){ex.printStackTrace();}}

public static void KeyinTest() {try(// 将Sytem.in对象转换成Reader对象InputStreamReader reader = new InputStreamReader(System.in);// 将普通Reader包装成BufferedReaderBufferedReader br = new BufferedReader(reader)){String line = null;// 采用循环方式来一行一行的读取while ((line = br.readLine()) != null){// 如果读取的字符串为"exit"，程序退出if (line.equals("exit")){System.exit(1);}// 打印读取的内容System.out.println("输入内容为:" + line);}}catch (IOException ioe){ioe.printStackTrace();}}

public static void pushbackTest() {try(// 创建一个PushbackReader对象，指定推回缓冲区的长度为64PushbackReader pr = new PushbackReader(new FileReader("a.txt") , 64)){char[] buf = new char[32];// 用以保存上次读取的字符串内容String lastContent = "";int hasRead = 0;// 循环读取文件内容while ((hasRead = pr.read(buf)) > 0){// 将读取的内容转换成字符串String content = new String(buf , 0 , hasRead);int targetIndex = 0;// 将上次读取的字符串和本次读取的字符串拼起来，// 查看是否包含目标字符串, 如果包含目标字符串if ((targetIndex = (lastContent + content).indexOf("测试")) > 0){// 将本次内容和上次内容一起推回缓冲区pr.unread((lastContent + content).toCharArray());// 重新定义一个长度为targetIndex的char数组if(targetIndex > 32){buf = new char[targetIndex];}// 再次读取指定长度的内容（就是目标字符串之前的内容）pr.read(buf , 0 , targetIndex);// 打印读取的内容System.out.print(new String(buf , 0 ,targetIndex));System.exit(0);}else{// 打印上次读取的内容System.out.print(lastContent);// 将本次内容设为上次读取的内容lastContent = content;}}}catch (IOException ioe){ioe.printStackTrace();}}

public static void readFromProcess() throws IOException {// 运行javac命令，返回运行该命令的子进程Process p = Runtime.getRuntime().exec("java -version");try(// 以p进程的错误流创建BufferedReader对象// 这个错误流对本程序是输入流，对p进程则是输出流BufferedReader br = new BufferedReader(newInputStreamReader(p.getErrorStream()))){String buff = null;// 采取循环方式来读取p进程的错误输出while((buff = br.readLine()) != null){System.out.println(buff);}}}

java version "1.8.0_51"
Java(TM) SE Runtime Environment (build 1.8.0_51-b16)
Java HotSpot(TM) 64-Bit Server VM (build 25.51-b03, mixed mode)

public class WriteToProcess
{public static void main(String[] args)throws IOException{// 运行java ReadStandard命令，返回运行该命令的子进程Process p = Runtime.getRuntime().exec("java ReadStandard");try(// 以p进程的输出流创建PrintStream对象// 这个输出流对本程序是输出流，对p进程则是输入流PrintStream ps = new PrintStream(p.getOutputStream())){// 向ReadStandard程序写入内容，这些内容将被ReadStandard读取ps.println("普通字符串");ps.println(new WriteToProcess());}}
}
// 定义一个ReadStandard类，该类可以接受标准输入，
// 并将标准输入写入out.txt文件。
class ReadStandard
{public static void main(String[] args){try(// 使用System.in创建Scanner对象，用于获取标准输入Scanner sc = new Scanner(System.in);PrintStream ps = new PrintStream(new FileOutputStream("out.txt"))){// 增加下面一行将只把回车作为分隔符sc.useDelimiter("\n");// 判断是否还有下一个输入项while(sc.hasNext()){// 输出输入项ps.println("键盘输入的内容是：" + sc.next());}}catch(IOException ioe){ioe.printStackTrace();}}
}

public static void randomAccessFileTest(){try(RandomAccessFile raf =  new RandomAccessFile("newFile.txt" , "r")){// 获取RandomAccessFile对象文件指针的位置，初始位置是0System.out.println("RandomAccessFile的文件指针的初始位置："+ raf.getFilePointer());// 移动raf的文件记录指针的位置raf.seek(30);byte[] bbuf = new byte[1024];// 用于保存实际读取的字节数int hasRead = 0;// 使用循环来重复“取水”过程while ((hasRead = raf.read(bbuf)) > 0 ){// 取出“竹筒”中水滴（字节），将字节数组转换成字符串输入！System.out.print(new String(bbuf , 0 , hasRead ));}}catch (IOException ex){ex.printStackTrace();}}

public static void insert(String fileName , long pos, String insertContent) throws IOException{File tmp = File.createTempFile("tmp" , null);tmp.deleteOnExit();try(RandomAccessFile raf = new RandomAccessFile(fileName , "rw");// 使用临时文件来保存插入点后的数据FileOutputStream tmpOut = new FileOutputStream(tmp);FileInputStream tmpIn = new FileInputStream(tmp)){raf.seek(pos);// ------下面代码将插入点后的内容读入临时文件中保存------byte[] bbuf = new byte[64];// 用于保存实际读取的字节数int hasRead = 0;// 使用循环方式读取插入点后的数据while ((hasRead = raf.read(bbuf)) > 0 ){// 将读取的数据写入临时文件tmpOut.write(bbuf , 0 , hasRead);}// ----------下面代码插入内容----------// 把文件记录指针重新定位到pos位置
                raf.seek(pos);// 追加需要插入的内容
                raf.write(insertContent.getBytes());// 追加临时文件中的内容while ((hasRead = tmpIn.read(bbuf)) > 0 ){raf.write(bbuf , 0 , hasRead);}}}

public static void main(String[] args){try(//以读、写方式打开一个RandomAccessFile对象RandomAccessFile raf = new RandomAccessFile("out.txt" , "rw")){//将记录指针移动到out.txt文件的最后
            raf.seek(raf.length());raf.write("追加的内容！\r\n".getBytes());}catch (IOException ex){ex.printStackTrace();}}

public static void writeObject() {try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("obj.txt"));) {LearnIO learnIO = new LearnIO("12334444444");oos.writeObject(learnIO);} catch (IOException ex) {// TODO: handle exception
            ex.printStackTrace();}}

//但是,如果如下

LearnIO learnIO = new LearnIO("12334444444");

oos.writeObject(learnIO);

learnIO.test="abcdetc";

//不会写入abcdetc,因为不会序列化号码相同的东西 oos.writeObject(learnIO);

public static void readObject(){try(ObjectInputStream ois = new ObjectInputStream(new FileInputStream("obj.txt"));){LearnIO learnIO = (LearnIO)ois.readObject();System.out.println(learnIO.test);}catch (Exception e) {// TODO: handle exception
            e.printStackTrace();}}