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java菜鸟学习实例（三）

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java菜鸟学习实例（三）java 菜鸟学习实例 三 java 实例

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Java实例

java菜鸟学习实例(一)
java菜鸟学习实例(二)
java菜鸟学习实例(三)
java菜鸟学习实例(四)
java菜鸟学习实例(完整版)

七.Java 目录操作

1.Java 实例 – 递归创建目录

import java.io.File; public class Main { 
         public static void main(String[] args) { 
         String directories = "D:\\a\\b\\c\\d\\e\\f\\g\\h\\i"; File file = new File(directories); boolean result = file.mkdirs(); System.out.println("Status = " + result); } }

2.Java 实例 – 删除目录

import java.io.File; public class Main { 
         public static void main(String[] argv) throws Exception { 
         // 删除当前目录下的 test 目录 deleteDir(new File("./test")); } public static boolean deleteDir(File dir) { 
         if (dir.isDirectory()) { 
         String[] children = dir.list(); for (int i = 0; i < children.length; i++) { 
         boolean success = deleteDir (new File(dir, children[i])); if (!success) { 
         return false; } } } if(dir.delete()) { 
         System.out.println("目录已被删除！"); return true; } else { 
         System.out.println("目录删除失败！"); return false; } } }

3.Java 实例 – 判断目录是否为空

import java.io.File; public class Main { 
         public static void main(String[] args) { 
         File file = new File("./testdir"); // 当前目录下的 testdir目录 if(file.isDirectory()){ 
         if(file.list().length>0){ 
         System.out.println("目录不为空!"); }else{ 
         System.out.println("目录为空!"); } }else{ 
         System.out.println("这不是一个目录!"); } } }

4.Java 实例 – 判断文件是否隐藏

import java.io.File; public class Main { 
         public static void main(String[] args) { 
         File file = new File("C:/Demo.txt"); System.out.println(file.isHidden()); } }

5.Java 实例 – 获取目录大小

import java.io.File; import org.apache.commons.io.FileUtils; public class Main { 
         public static void main(String[] args) { 
         long size = FileUtils.sizeOfDirectory(new File("C:/test")); System.out.println("Size: " + size + " bytes"); } }

6.Java 实例 – 在指定目录中查找文件

import java.io.File; public class Main { 
         public static void main(String[] argv) throws Exception { 
         File dir = new File("../java"); String[] children = dir.list(); if (children == null) { 
         System.out.println("该目录不存在"); } else { 
         for (int i = 0; i < children.length; i++) { 
         String filename = children[i]; System.out.println(filename); } } } }

7.Java 实例 – 获取文件的上级目录

import java.io.File; public class Main { 
         public static void main(String[] args) { 
         File file = new File("C:/File/demo.txt"); String strParentDirectory = file.getParent(); System.out.println("文件的上级目录为 : " + strParentDirectory); } }

8.Java 实例 – 获取目录最后修改时间

import java.io.File; import java.util.Date; public class Main { 
         public static void main(String[] args) { 
         File file = new File("C://FileIO//demo.txt"); System.out.println("最后修改时间：" + new Date(file.lastModified())); } }

9.Java 实例 – 打印目录结构

import java.io.File; import java.io.IOException; public class FileUtil { 
         public static void main(String[] a)throws IOException{ 
         showDir(1, new File("d:\\Java")); } static void showDir(int indent, File file) throws IOException { 
         for (int i = 0; i < indent; i++) System.out.print('-'); System.out.println(file.getName()); if (file.isDirectory()) { 
         File[] files = file.listFiles(); for (int i = 0; i < files.length; i++) showDir(indent + 4, files[i]); } } }

10.Java 实例 – 遍历指定目录下的所有目录

import java.io.*; class Main { 
         public static void main(String[] args) { 
         File dir = new File("F:"); File[] files = dir.listFiles(); FileFilter fileFilter = new FileFilter() { 
         public boolean accept(File file) { 
         return file.isDirectory(); } }; files = dir.listFiles(fileFilter); System.out.println(files.length); if (files.length == 0) { 
         System.out.println("目录不存在或它不是一个目录"); } else { 
         for (int i=0; i< files.length; i++) { 
         File filename = files[i]; System.out.println(filename.toString()); } } } }

11.Java 实例 – 遍历指定目录下的所有文件

import java.io.File; class Main { 
         public static void main(String[] args) { 
         File dir = new File("C:"); String[] children = dir.list(); if (children == null) { 
         System.out.println( "目录不存在或它不是一个目录"); } else { 
         for (int i=0; i< children.length; i++) { 
         String filename = children[i]; System.out.println(filename); } } } }

12.Java 实例 – 在指定目录中查找文件

import java.io.*; class Main { 
         public static void main(String[] args) { 
         File dir = new File("C:"); FilenameFilter filter = new FilenameFilter() { 
         public boolean accept (File dir, String name) { 
         return name.startsWith("b"); } }; String[] children = dir.list(filter); if (children == null) { 
         System.out.println("目录不存在或它不是一个目录"); } else { 
         for (int i=0; i < children.length; i++) { 
         String filename = children[i]; System.out.println(filename); } } } }

13.Java 实例 – 遍历系统根目录

import java.io.*; class Main{ 
         public static void main(String[] args){ 
         File[] roots = File.listRoots(); System.out.println("系统所有根目录："); for (int i=0; i < roots.length; i++) { 
         System.out.println(roots[i].toString()); } } }

14.Java 实例 – 查看当前工作目录

class Main { 
         public static void main(String[] args) { 
         String curDir = System.getProperty("user.dir"); System.out.println("你当前的工作目录为 :" + curDir); } }

15.Java 实例 – 遍历目录

import java.io.File; public class Main { 
         public static void main(String[] argv) throws Exception { 
         System.out.println("遍历目录"); File dir = new File("/www/java"); //要遍历的目录 visitAllDirsAndFiles(dir); } public static void visitAllDirsAndFiles(File dir) { 
         System.out.println(dir); if (dir.isDirectory()) { 
         String[] children = dir.list(); for (int i = 0; i < children.length; i++) { 
         visitAllDirsAndFiles(new File(dir, children[i])); } } } }

八.Java 异常处理

1.Java 实例 – 异常处理方法

class ExceptionDemo { 
         public static void main(String[] args) { 
         try { 
         throw new Exception("My Exception"); } catch (Exception e) { 
         System.err.println("Caught Exception"); System.err.println("getMessage():" + e.getMessage()); System.err.println("getLocalizedMessage():" + e.getLocalizedMessage()); System.err.println("toString():" + e); System.err.println("printStackTrace():"); e.printStackTrace(); } } }

2.Java 实例 – 多个异常处理（多个catch）

class Demo { 
         int div(int a,int b) throws ArithmeticException,ArrayIndexOutOfBoundsException//在功能上通过throws的关键字声明该功能可能出现问题  { 
         int []arr = new int [a]; System.out.println(arr[4]);//制造的第一处异常  return a/b;//制造的第二处异常  } } class ExceptionDemo { 
         public static void main(String[]args) //throws Exception  { 
         Demo d = new Demo(); try { 
         int x = d.div(4,0);//程序运行截图中的三组示例 分别对应此处的三行代码  //int x = d.div(5,0);  //int x = d.div(4,1);  System.out.println("x="+x); } catch (ArithmeticException e) { 
         System.out.println(e.toString()); } catch (ArrayIndexOutOfBoundsException e) { 
         System.out.println(e.toString()); } catch (Exception e)//父类 写在此处是为了捕捉其他没预料到的异常 只能写在子类异常的代码后面  //不过一般情况下是不写的  { 
         System.out.println(e.toString()); } System.out.println("Over"); } }

3.Java 实例 – Finally的用法

public class ExceptionDemo2 { 
         public static void main(String[] argv) { 
         new ExceptionDemo2().doTheWork(); } public void doTheWork() { 
         Object o = null; for (int i=0; i<5; i++) { 
         try { 
         o = makeObj(i); } catch (IllegalArgumentException e) { 
         System.err.println ("Error: ("+ e.getMessage()+")."); return; } finally { 
         System.err.println("都已执行完毕"); if (o==null) System.exit(0); } System.out.println(o); } } public Object makeObj(int type) throws IllegalArgumentException { 
         if (type == 1) throw new IllegalArgumentException ("不是指定的类型： " + type); return new Object(); } }

4.Java 实例 – 使用 catch 处理异常

public class Main { 
         public static void main (String args[]) { 
         int array[]={ 
        20,20,40}; int num1=15,num2=10; int result=10; try{ 
         result = num1/num2; System.out.println("结果为 " +result); for(int i =5;i >=0; i--) { 
         System.out.println ("数组的元素值为 " +array[i]); } } catch (Exception e) { 
         System.out.println("触发异常 : "+e); } } }

5.Java 实例 – 多线程异常处理

class MyThread extends Thread{ 
         public void run(){ 
         System.out.println("Throwing in " +"MyThread"); throw new RuntimeException(); } } class Main { 
         public static void main(String[] args){ 
         MyThread t = new MyThread(); t.start(); try{ 
         Thread.sleep(1000); } catch (Exception x){ 
         System.out.println("Caught it" + x); } System.out.println("Exiting main"); } }

6.Java 实例 – 获取异常的堆栈信息

public class Main{ 
         public static void main (String args[]){ 
         int array[]={ 
        20,20,40}; int num1=15,num2=10; int result=10; try{ 
         result = num1/num2; System.out.println("The result is" +result); for(int i =5; i>=0; i--) { 
         System.out.println("The value of array is" +array[i]); } } catch (Exception e) { 
         e.printStackTrace(); } } }

7.Java 实例 – 重载方法异常处理

public class Main { 
         double method(int i) throws Exception{ 
         return i/0; } boolean method(boolean b) { 
         return !b; } static double method(int x, double y) throws Exception { 
         return x + y ; } static double method(double x, double y) { 
         return x + y - 3; } public static void main(String[] args) { 
         Main mn = new Main(); try{ 
         System.out.println(method(10, 20.0)); System.out.println(method(10.0, 20)); System.out.println(method(10.0, 20.0)); System.out.println(mn.method(10)); } catch (Exception ex){ 
         System.out.println("exception occoure: "+ ex); } } }

8.Java 实例 – 链试异常

public class Main { 
         public static void main (String args[])throws Exception { 
         int n=20,result=0; try{ 
         result=n/0; System.out.println("结果为"+result); } catch(ArithmeticException ex){ 
         System.out.println("发算术异常: "+ex); try { 
         throw new NumberFormatException(); } catch(NumberFormatException ex1) { 
         System.out.println("手动抛出链试异常 : "+ex1); } } } }

9.Java 实例 – 自定义异常

class WrongInputException extends Exception { 
         // 自定义的类 WrongInputException(String s) { 
         super(s); } } class Input { 
         void method() throws WrongInputException { 
         throw new WrongInputException("Wrong input"); // 抛出自定义的类 } } class TestInput { 
         public static void main(String[] args){ 
         try { 
         new Input().method(); } catch(WrongInputException wie) { 
         System.out.println(wie.getMessage()); } } }

九.Java 数据结构

1.Java 实例 – 数字求和运算

public class Main { 
         public static void main(String[] args) { 
         int limit=100; int sum=0; int i=1; do { 
         sum=sum+i; i++; } while(i<=limit); System.out.println("sum="+sum); } }

2.Java 实例 – 利用堆栈将中缀表达式转换成后缀

import java.io.IOException; public class InToPost { 
         private Stack theStack; private String input; private String output = ""; public InToPost(String in) { 
         input = in; int stackSize = input.length(); theStack = new Stack(stackSize); } public String doTrans() { 
         for (int j = 0; j < input.length(); j++) { 
         char ch = input.charAt(j); switch (ch) { 
         case '+': case '-': gotOper(ch, 1); break; case '*': case '/': gotOper(ch, 2); break; case '(': theStack.push(ch); break; case ')': gotParen(ch); break; default: output = output + ch; break; } } while (!theStack.isEmpty()) { 
         output = output + theStack.pop(); } System.out.println(output); return output; } public void gotOper(char opThis, int prec1) { 
         while (!theStack.isEmpty()) { 
         char opTop = theStack.pop(); if (opTop == '(') { 
         theStack.push(opTop); break; } else { 
         int prec2; if (opTop == '+' || opTop == '-') prec2 = 1; else prec2 = 2; if (prec2 < prec1) { 
         theStack.push(opTop); break; } else output = output + opTop; } } theStack.push(opThis); } public void gotParen(char ch){ 
         while (!theStack.isEmpty()) { 
         char chx = theStack.pop(); if (chx == '(') break; else output = output + chx; } } public static void main(String[] args) throws IOException { 
         String input = "1+2*4/5-7+3/6"; String output; InToPost theTrans = new InToPost(input); output = theTrans.doTrans(); System.out.println("Postfix is " + output + '\n'); } class Stack { 
         private int maxSize; private char[] stackArray; private int top; public Stack(int max) { 
         maxSize = max; stackArray = new char[maxSize]; top = -1; } public void push(char j) { 
         stackArray[++top] = j; } public char pop() { 
         return stackArray[top--]; } public char peek() { 
         return stackArray[top]; } public boolean isEmpty() { 
         return (top == -1); } } }

3.Java 实例 – 在链表（LinkedList）的开头和结尾

import java.util.LinkedList; public class Main { 
         public static void main(String[] args) { 
         LinkedList<String> lList = new LinkedList<String>(); lList.add("1"); lList.add("2"); lList.add("3"); lList.add("4"); lList.add("5"); System.out.println(lList); lList.addFirst("0"); System.out.println(lList); lList.addLast("6"); System.out.println(lList); } }

4.Java 实例 – 获取链表（LinkedList）的第一个

import java.util.LinkedList; public class Main { 
         public static void main(String[] args) { 
         LinkedList<String> lList = new LinkedList<String>(); lList.add("100"); lList.add("200"); lList.add("300"); lList.add("400"); lList.add("500"); System.out.println("链表的第一个元素是：" + lList.getFirst()); System.out.println("链表的最后一个元素是：" + lList.getLast()); } }

5.Java 实例 – 删除链表中的元素

import java.util.*; public class Main { 
         public static void main(String[] args) { 
         LinkedList<String> lList = new LinkedList<String>(); lList.add("1"); lList.add("8"); lList.add("6"); lList.add("4"); lList.add("5"); System.out.println(lList); lList.subList(2, 4).clear(); System.out.println(lList); } }

6.Java 实例 – 获取链表的元素

import java.util.*; public class Main { 
         private LinkedList list = new LinkedList(); public void push(Object v) { 
         list.addFirst(v); } public Object top() { 
         return list.getFirst(); } public Object pop() { 
         return list.removeFirst(); } public static void main(String[] args) { 
         Main stack = new Main(); for (int i = 30; i < 40; i++) stack.push(new Integer(i)); System.out.println(stack.top()); System.out.println(stack.pop()); System.out.println(stack.pop()); System.out.println(stack.pop()); } }

7.Java 实例 – 获取向量元素的索引值

import java.util.Collections; import java.util.Vector; public class Main { 
         public static void main(String[] args) { 
         Vector v = new Vector(); v.add("X"); v.add("M"); v.add("D"); v.add("A"); v.add("O"); Collections.sort(v); System.out.println(v); int index = Collections.binarySearch(v, "D"); System.out.println("元素索引值为 : " + index); } }

8.Java 实例 – 栈的实现

]`public class MyStack { 
         private int maxSize; private long[] stackArray; private int top; public MyStack(int s) { 
         maxSize = s; stackArray = new long[maxSize]; top = -1; } public void push(long j) { 
         stackArray[++top] = j; } public long pop() { 
         return stackArray[top--]; } public long peek() { 
         return stackArray[top]; } public boolean isEmpty() { 
         return (top == -1); } public boolean isFull() { 
         return (top == maxSize - 1); } public static void main(String[] args) { 
         MyStack theStack = new MyStack(10); theStack.push(10); theStack.push(20); theStack.push(30); theStack.push(40); theStack.push(50); while (!theStack.isEmpty()) { 
         long value = theStack.pop(); System.out.print(value); System.out.print(" "); } System.out.println(""); } }`

9.Java 实例 – 链表元素查找

import java.util.LinkedList; public class Main { 
         public static void main(String[] args) { 
         LinkedList lList = new LinkedList(); lList.add("1"); lList.add("2"); lList.add("3"); lList.add("4"); lList.add("5"); lList.add("2"); System.out.println("元素 2 第一次出现的位置：" + lList.indexOf("2")); System.out.println("元素 2 最后一次出现的位置："+ lList.lastIndexOf("2")); } }

10.Java 实例 – 压栈出栈的方法实现字符串反转

import java.io.IOException; public class StringReverserThroughStack { 
         private String input; private String output; public StringReverserThroughStack(String in) { 
         input = in; } public String doRev() { 
         int stackSize = input.length(); Stack theStack = new Stack(stackSize); for (int i = 0; i < input.length(); i++) { 
         char ch = input.charAt(i); theStack.push(ch); } output = ""; while (!theStack.isEmpty()) { 
         char ch = theStack.pop(); output = output + ch; } return output; } public static void main(String[] args) throws IOException { 
         String input = "www.w3cschool.cc"; String output; StringReverserThroughStack theReverser = new StringReverserThroughStack(input); output = theReverser.doRev(); System.out.println("反转前： " + input); System.out.println("反转后： " + output); } class Stack { 
         private int maxSize; private char[] stackArray; private int top; public Stack(int max) { 
         maxSize = max; stackArray = new char[maxSize]; top = -1; } public void push(char j) { 
         stackArray[++top] = j; } public char pop() { 
         return stackArray[top--]; } public char peek() { 
         return stackArray[top]; } public boolean isEmpty() { 
         return (top == -1); } } }

11.Java 实例 – 队列（Queue）用法

import java.util.LinkedList; import java.util.Queue; public class Main { 
         public static void main(String[] args) { 
         //add()和remove()方法在失败的时候会抛出异常(不推荐) Queue<String> queue = new LinkedList<String>(); //添加元素 queue.offer("a"); queue.offer("b"); queue.offer("c"); queue.offer("d"); queue.offer("e"); for(String q : queue){ 
         System.out.println(q); } System.out.println("==="); System.out.println("poll="+queue.poll()); //返回第一个元素，并在队列中删除 for(String q : queue){ 
         System.out.println(q); } System.out.println("==="); System.out.println("element="+queue.element()); //返回第一个元素  for(String q : queue){ 
         System.out.println(q); } System.out.println("==="); System.out.println("peek="+queue.peek()); //返回第一个元素  for(String q : queue){ 
         System.out.println(q); } } }

12.Java 实例 – 获取向量的最大元素

import java.util.Collections; import java.util.Vector; public class Main { 
         public static void main(String[] args) { 
         Vector v = new Vector(); v.add(new Double("3.4324")); v.add(new Double("3.3532")); v.add(new Double("3.342")); v.add(new Double("3.349")); v.add(new Double("2.3")); Object obj = Collections.max(v); System.out.println("最大元素是："+obj); } }

13.Java 实例 – 链表修改

import java.util.LinkedList; public class Main { 
         public static void main(String[] a) { 
         LinkedList officers = new LinkedList(); officers.add("B"); officers.add("B"); officers.add("T"); officers.add("H"); officers.add("P"); System.out.println(officers); officers.set(2, "M"); System.out.println(officers); } }

14.Java 实例 – 旋转向量

import java.util.Collections; import java.util.Vector; public class Main { 
         public static void main(String[] args) { 
         Vector<String> v = new Vector(); v.add("1"); v.add("2"); v.add("3"); v.add("4"); v.add("5"); System.out.println(v); Collections.swap(v, 0, 4); System.out.println("旋转后"); System.out.println(v); } }






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