java int pos 1_长文慎点，Java学习笔记（一）

你的名字 2022-11-10 05:23 129阅读 0赞

这只是一篇我自己学习java的流水账笔记，包含了以下内容，全是基础代码示例，希望对正在学习java的小伙伴有帮助

基础类型转换: The convertion of basic data types

字符串统计: String counting functions

冒泡排序，选择排序，二分法查找：bubbleSort , selectionSort & binarySearch

打印文件树：Listing files tree of a path typed from command line

java流的基本操作：Java Input/Output stream

The convertion of basic data types

char to int

When converting a char into an int , you\`ll get the ASCII value of a character.

Convert character to ASCII

int ascii = (int)char;

Convert ASCII to character

ascii is an int below

char char = (char)ascii;

Example code

public class CharToAscii\{

public static void main(String\[\] args)\{

System.out.println(charToAscii('a'));//97

System.out.println(asciiToChar(97));//a

public static int charToAscii(char c)\{

int ascii = c;

return ascii;

public static char asciiToChar(int ascii)\{

char c = (char)ascii;

return c;

String counting functions

First String counting

How to count a string : How many uppercase letters , lowercase letters and other symbols ? Like this:

String str = "AqSwDeFrGtgHJhhhKgfgf!@\#$%^7898754";/\* How many uppercase letters

lowercase letters and other symbols here ? \*/

Here are 3 ways to do it:

Function\_1:There\`s a tip about basic data convertion char to int

public static void fun\_1(String s)\{

int lCount = 0, uCount = 0, oCount = 0;

for (int i = 0;i < s.length();i++)\{

char c = s.charAt(i);

if (c >= 'a' && c <= 'z')\{//char to ascii

lCount++;

\}else if(c >= 'A' && c <= 'Z')\{

uCount++;

\} else\{

oCount++;

\};

System.out.println

("There are " + lCount + "uppercase letters!" );

System.out.println

("There are " + uCount + "lowercase letters!" );

System.out.println

("There are " + oCount + "other symbols!" );

Function\_2:Class String has the indexOf() methods

public static void fun\_2(String s)\{

String lower = "abcdefghijklmnopqrstuvwxyz";

String upper = "ABCDEFGHIJKLMNOPKQSTUVWXYZ";

int lCount = 0, uCount = 0, oCount = 0;

for (int i = 0;i < s.length();i++)\{

char c = s.charAt(i);

if ( lower.indexOf(c) != -1 )\{

lCount++;

\}else if(upper.indexOf(c) != -1)\{

uCount++;

\} else\{

oCount++;

\};

System.out.println

("There are " + lCount + "uppercase letters!" );

System.out.println

("There are " + lCount + "lowercase letters!" );

System.out.println

("There are " + lCount + "other symbols!" );

Function\_3:Using the charAt() , Character.isUpperCase() and Character.isLowerCase() method

public static void fun\_3(String s)\{

int lCount = 0, uCount = 0, oCount = 0;

for (int i = 0;i < s.length();i++)\{

char c = s.charAt(i);

if (Character.isLowerCase(c))\{

lCount++;

\}else if(Character.isUpperCase(c))\{

uCount++;

\} else\{

oCount++;

\};

System.out.println

("There are " + lCount + "uppercase letters!" );

System.out.println

("There are " + lCount + "lowercase letters!" );

System.out.println

("There are " + lCount + "other symbols!" );

Second String counting

How to count a string : How many String pointed here? Like this:

String str = "javartyjojavayyuhujavatyuuhueuhdjavajiiuhdsuhjava";

String s ="java"// How many s in str ?

Here are 2 ways to do it:

Function\_1: 3 methods here : substring() , equals() , indexOf()

public static void fun\_1(String str , String s)\{

int Count = 0, restore = 0,index = 0;

String s\_start = str.substring(0,s.length());

if(s\_start.equals(s))\{Count = 1;\}

while(index != -1 )\{

index = str.indexOf(s , s.length() + restore);

if( index >= 0 )\{ Count++; \}

restore = index;

System.out.println

("\\""+ s + "\\"" + " appears "+ Count +"times");

Function\_2: 2 methods here : substring() , indexOf()

public static void fun\_2(String str , String s)\{

int Count = 0,index = -1;

while( (index = str.indexOf(s)) != -1)\{

str = str.substring(index + s.length());

Count ++;

System.out.println

("\\""+ s + "\\"" + " appears "+ Count +"times");

bubbleSort , selectionSort & binarySearch

The source code here

public class Test\{

public static void main(String\[\] args)\{

Date\[\] d = new Date\[4\];

d\[0\] = new Date(1994,8,20);

d\[1\] = new Date(1992,7,12);

d\[2\] = new Date(2016,8,20);

d\[3\] = new Date(1990,6,23);

Date ds = new Date(2016,8,20);

System.out.println("Original:");

print(d);

System.out.println("class Date serached:"+ds);

System.out.println();

System.out.println("selectionSort below:");

selectionSort(d);

print(d);

System.out.println("index searched below:");

System.out.println

(binarySearch(d,ds));

System.out.println("bubbleSort below:");

bubbleSort(d);

print(d);

System.out.println("index searched below:");

System.out.println

(binarySearch(d,ds));

public static void print(Date\[\] date)\{

for(int i = 0;i < date.length;i++)\{

System.out.println(date\[i\]);

public static void selectionSort(Date\[\] date)\{

Date temp;

for (int i = 0;i < date.length ; i++ )\{

for (int j = i;j < date.length; j++ )\{

if( date\[i\].compare(date\[j\]) > 0 )\{

temp = date\[i\];

date\[i\] = date\[j\];

date\[j\] = temp;

public static void bubbleSort(Date\[\] date)\{

Date temp;

for (int i = date.length - 1;i > 0 ;i-- )\{

for (int j = 0;j < i;j++)\{

if( date\[j\].compare(date\[j+1\]) > 0 )\{

temp = date\[j\];

date\[j\] = date\[j+1\];

date\[j+1\] = temp;

public static int binarySearch(Date\[\] date,Date d)\{

if (date.length == 0)\{return -1;\}

int startPos = 0;

int endPos = date.length - 1;

int middlePos = (startPos + endPos)/2;

while (startPos <= endPos )\{

if (d.compare(date\[middlePos\]) == 0)\{

return middlePos;

if (d.compare(date\[middlePos\]) > 0)\{

startPos = middlePos + 1;

if (d.compare(date\[middlePos\]) < 0)\{

endPos = middlePos - 1;

middlePos = (startPos + endPos)/2;

return -1;

class Date\{

private int day,month,year;

Date(int y,int m,int d)\{

this.year = y;

this.month = m;

this.day = d;

public int compare(Date date)\{//ternary operator

return

year > date.year ? 1

:year < date.year ? -1

:month > date.month ? 1

:month < date.month ? -1

:day > date.day ? 1

:day < date.day ? -1 : 0;

public String toString()\{//class Object method toString()

String s = new String(year+"-"+ month+"-"+ day);

return s;

Listing files tree of a path typed from command line

import java.io.\*;

public class ListFilesTree\{

public static void main(String\[\] args)\{//reading a path from command line

String path = args\[0\].replace(File.separatorChar,'/');

//converting separator

File file = new File(path);

fileTree(file,0);

public static void fileTree(File f,int level)\{//level denotes the depth of path

String preStr = "";

for (int i = 0;i < level;i++)\{

preStr += "---|";

File\[\] flist = f.listFiles();

for (int i = 0;i < flist.length;i++)\{

System.out.println(preStr + flist\[i\]);

if( flist\[i\].isDirectory() )\{

fileTree(flist\[i\],level + 1);/\*calling the

fileTree itself is a recursion

level increase 1 when calling fileTree everytime

\*/

Java Input/Output stream

FileInputStream & FileOutputStream

import java.io.\*;

public class TestFileOutputStream\{

public static void main(String\[\] args)\{

int b = 0;

FileInputStream in = null;

FileOutputStream out = null;

String inPath =

"D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\TestFileOutputStream.java";

String outPath =

"D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\CopyTestFileOutputStream.java";

try\{

in = new FileInputStream(inPath.replace(File.separatorChar,'/'));

out = new FileOutputStream(outPath.replace(File.separatorChar,'/'));

while ( (b = in.read()) != -1)\{

out.write(b);

System.out.print((char)b);

in.close();out.close();

\}catch(FileNotFoundException e)\{

System.out.println("File not found!");

System.exit(-1);

\}catch (IOException e1)\{

System.out.println("io error!");

System.exit(-1);

System.out.println("文件已经复制");

FileReader & FileWriter

import java.io.\*;

public class TestFileReader\{

public static void main(String\[\] args)\{

int c = 0;

FileReader fr = null;

FileWriter fw = null;

String frPath =

"D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\TestFileReader.java";

String fwPath =

"D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\copyTestFileReader.java";

try\{

fr = new FileReader(frPath.replace(File.separatorChar,'/'));

fw = new FileWriter(fwPath.replace(File.separatorChar,'/'));

while ((c = fr.read()) != -1 )\{

fw.write(c);

System.out.print((char)c);

fr.close();

fw.close();

\}catch(FileNotFoundException e)\{

System.out.println("文件找不到！");

System.exit(-1);

\}catch(IOException e1)\{

System.out.println("文件错误！");

System.exit(-1);

System.out.println("文件已复制！");

import java.io.\*;

public class TestFileWriter\{

public static void main(String\[\] args)\{

FileWriter fw = null;

try\{

fw = new FileWriter

("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Unicode.dat");

for (int c = 0;c <= 50000;c++)\{

fw.write(c);

fw.close();

\}catch(FileNotFoundException e)\{

System.out.println("文件找不到！");

System.exit(-1);

\}catch(IOException e1)\{

System.out.println("IO错误！");

System.exit(-1);

Buffered Stream

import java.io.\*;

public class TestBuffered\{

public static void main(String\[\] args)\{

try\{

FileInputStream in = new FileInputStream

("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\TestBuffered.java");

BufferedInputStream bis = new BufferedInputStream(in);

System.out.println((char)bis.read());

int c = 0;

for(int i = 0;i <= 100 && (c = bis.read()) != -1;i++ )\{

System.out.print((char)c+"");

\}catch(IOException e)\{e.printStackTrace();\}

import java.io.\*;

public class TestBufferWriter\{

public static void main(String\[\] args)\{

try\{

BufferedWriter bw = new BufferedWriter

(new FileWriter("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\1.txt"));

BufferedReader br = new BufferedReader

(new FileReader("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\1.txt"));

String s = null;

for(int i = 0;i < 10;i++)\{

s = String.valueOf(Math.random());

bw.write(s);

bw.newLine();

bw.flush();

while( (s = br.readLine()) != null)\{

System.out.println(s);

bw.close();br.close();

\}catch(IOException e)\{e.printStackTrace();\}

Converting Stream

import java.io.\*;

public class Transform\{

public static void main(String\[\] args)\{

try\{

String path =

"D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\transform.txt";

OutputStreamWriter osw = new OutputStreamWriter

(new FileOutputStream(path));

osw.write("output stream writer transforms the file output stream!");

System.out.println(osw.getEncoding());

osw.close();

osw = new OutputStreamWriter

((new FileOutputStream(path,true)),"ISO8859\_1");

osw.write("output stream writer transforms the file output stream!");

System.out.println(osw.getEncoding());

osw.close();

\}catch(IOException e)\{

e.printStackTrace();

import java.io.\*;

public class Transform1\{

public static void main(String\[\] args)\{

InputStreamReader isr = new InputStreamReader(System.in);//阻塞式的方法

BufferedReader br = new BufferedReader(isr);

String s = null;

try \{

s = br.readLine();

while(s != null)\{

if (s.equalsIgnoreCase("exit"))\{System.exit(-1);\}

System.out.println(s.toUpperCase());

s = br.readLine();

br.close();

\}catch(IOException e)\{

e.printStackTrace();

Data Stream

import java.io.\*;

public class DataStream\{

public static void main(String\[\] args)\{

ByteArrayOutputStream baos = new ByteArrayOutputStream();

DataOutputStream dos = new DataOutputStream(baos);

try \{

dos.writeDouble(Math.random());

dos.writeBoolean(true);

ByteArrayInputStream bais = new ByteArrayInputStream

(baos.toByteArray());

System.out.println(bais.available());

DataInputStream dis = new DataInputStream(bais);

System.out.println(dis.readDouble());

System.out.println(dis.readBoolean());

\}catch (IOException e)\{e.printStackTrace();\}

Printing Stream

import java.io.\*;

public class TestPrintStream1\{

public static void main(String\[\] args)\{

String f = args\[0\];

if (f != null)\{

list(f,System.out);

public static void list(String f,PrintStream ps)\{

try\{

BufferedReader br = new BufferedReader

(new FileReader(f));

while( br.readLine()!= null)\{

ps.println(br.readLine());

br.close();

\}catch (IOException e)\{e.printStackTrace();\}

import java.io.\*;

import java.util.\*;

public class TestPrintStream2\{

public static void main(String\[\] args)\{

BufferedReader br = new BufferedReader

(new InputStreamReader(System.in));

try\{

String s = null;

FileWriter fw = new FileWriter

("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\log.txt",true);

PrintWriter log = new PrintWriter(fw);

while( (s = br.readLine()) != null)\{

if(s.equalsIgnoreCase("exit")) break;

System.out.println(s.toUpperCase());

log.println("-------");

log.println(s.toUpperCase());

log.flush();

log.println("===="+new Date()+"=====");

log.flush();

log.close();

\}catch(IOException e)\{e.printStackTrace();\}

Object Stream

import java.io.\*;

public class TestObjectStream\{

public static void main(String\[\] args)\{

T t = new T();

t.i = 8;

try\{

FileOutputStream fos = new FileOutputStream

("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\object.dat");

ObjectOutputStream oos = new ObjectOutputStream(fos);

oos.writeObject(t);

oos.flush();

oos.close();

FileInputStream fis = new FileInputStream

("D:\\\\Important files\\\\JAVA\\\\practice\\\\IO\\\\Test\\\\object.dat");

ObjectInputStream ois = new ObjectInputStream(fis);

T tread = (T)ois.readObject();

System.out.println

(tread.i+" "+tread.j+" "+tread.d+" "+tread.k);

\}catch(IOException e )\{e.printStackTrace();

\}catch(ClassNotFoundException e)\{e.printStackTrace();\}

class T implements Serializable\{

int i = 10;

int j = 9;

double d = 0.12324;

transient int k = 15;

java int pos 1_长文慎点，Java学习笔记（一）

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