Network, IO flow, reflection, multithreading, exception

---

---

One 、 Establish client and host connections （ The Internet ）

• host

package text;

import java.io.IOException;  // Import   This package is used to catch input and output exceptions  
import java.io.InputStream; // yes java Standard library provides the most basic input stream , It's an abstract class , Is a superclass of all input streams 
import java.net.ServerSocket;  // Server socket   Server program and IP Address binding 
import java.net.Socket;  //  Client initialized a socket Connect , To connect to the server , Two programs on the network exchange data through a two-way communication connection , One end of this two-way link is called a Socket. Any one of them Socket It's all by IP The address and port number are uniquely determined .



public class Java03 {
    
	public static void main(String []args) throws IOException {
    
		//TODO  The server-side code is as follows ：
		//ip： Equivalent to host number 
		//port： Extension number 
		
		// Create a server-side socket 、 Specify port number 
		ServerSocket ss=new ServerSocket(1009);
		// Receiving request 、 And returns the socket 
		Socket s=ss.accept();
		
		InputStream is=s.getInputStream();
		byte [] b=new byte[1024];
		int i=is.read(b);
		String str=new String(b,0,i);
		System.out.println(str);
		
		while(true){
       // while The loop wraps the code   can   Receive messages from multiple clients 
			
		}
	}
}

• The client

package text;

import java.io.IOException;  // Import   This package is used to catch input and output exceptions 
import java.io.OutputStream;  // Use OutputStream Stream output file 
import java.net.Socket;      // Client initialized a socket Connect , To connect to the server , Two programs on the network exchange data through a two-way communication connection , One end of this two-way link is called a Socket. Any one of them Socket It's all by IP The address and port number are uniquely determined .

import java.net.UnknownHostException;

public class Java04 {
    
	public static void main(String[] args) throws UnknownHostException, IOException {
    
		//TODO  The client code is as follows ：
		//  Create socket object , Must specify ip and port
		Socket s=new Socket("192.168.10.37",1009);
		OutputStream o=s.getOutputStream();
		String str="hallo";
		o.write(str.getBytes());
	}
}

---

Two 、I/O system

• I / O ： Input/Output      read / Write      Input / Output
  Byte stream ： Read and write in bytes ：byte[ ]
  Byte input stream ：java.io.InputStream
  Byte output stream ：java.io.OutputStream

  Character stream ： Read and write in character mode ：char[ ]
  The input stream of the child character ：java.io.Reader
  The output stream of characters ：java.io.Writer

• Read and write local files

package page;
import java.io.FileReader;// File input character stream 
import java.io.IOException;
import java.io.BufferedReader; // Buffer flow 
import java.io.FileNotFoundException;  // Throw an exception 

public class Java05 {
    
	public static void main(String[] args) throws IOException {
    
		// TODO Auto-generated method stub
				// Read native files 
				/ The first step is to create a file input stream 
					FileReader f=new FileReader("d:/1.txt");
					// The second step   Create a buffered stream object 
					BufferedReader b=new BufferedReader(f);
					String s="";
					while((s=b.readLine())!=null) {
    
						System.out.println(s);
					}
					// The third step   close IO flow 
					b.close();
					f.close();
	}
}

• Native write file

package page;
import java.io.FileWriter;  // Write 
import java.io.IOException;
import java.io.BufferedWriter;	// Write buffer 
public class Java06 {
    
	public static void main(String[] args) throws IOException {
    
		FileWriter f=new FileWriter("D:/2.txt",true); //true  Adding after does not overwrite , conversely 
		BufferedWriter b=new BufferedWriter(f);
		b.write("Hallo123"+"\r"); // \r  or \n  Line break 
		b.close();
		f.close();
	}
}

---

3、 ... and 、 Reflection

(1) java Reflection API

• java.lang.Class                   class
• java.lang.reflect.Field         Member variables
• java.lang.reflect.Method     Member method
• java.lang.reflect.Constructor Construction method

package text;
import java.lang.Class;
import java.lang.reflect.Field; // member object 
import java.lang.reflect.Method;// Member method 
import java.lang.reflect.Constructor; // Construction method 



public class Java01 {
    
	public static void main(String[] args) throws ClassNotFoundException, InstantiationException, IllegalAccessException {
    
		// Create objects with reflections  iop Inversion of control  @  The underlying implementation functions   Create objects with reflections  instance  obtain  
		Class J=Class.forName("text.Java02");
		Java02 j2=(Java02) J.newInstance();
		j2.setAge(2);
		System.out.println(j2);
	}
}

---

Four 、 Multithreading

• Mode one ： By inheritance Thread Class to implement multithreading

• Mode two ： By implementing Runnable Interface to implement multithreading

• Mode one Rhread Realization

package page;

public class T1 extends Thread {
    

	// This is the core business method of the thread 
	public void run() {
    
		
		while(true) {
    
			System.out.println(Thread.currentThread().getName());
		}
		
	}
		
	
}

• Start the inheritance Thread
  

---

• Mode two Runnable Interface to implement

package page;

public class T2 implements Runnable {
    

	
	public void run() {
    
		// This is the core business method of the thread 
		
			
			while(true) {
    
				System.out.println(Thread.currentThread().getName());
			}
			
		}
			

	

}

• Start implementation Runnable Interface
  

---

5、 ... and 、 abnormal

package page;

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Random;

public class Java07 {
    
	public static void main(String []args) throws FileNotFoundException {
    
		//（1）  Arithmetic abnormality ： java.lang.ArithmeticException 
		int a=3/0;
		
		//（2）  Null pointer exception ： java.lang.NullpointerException
		String s=null;
		System.out.println(s.equals("123"));
		
		//（3） Array subscript out of bounds ： java.lang.ArrayIndexOutOfBoundsException
		int [] arr= {
    1,2,3};
		System.out.println(arr[3]);
		
		//（4） Type conversion exception ： java.lang.ClassCastException
		Object o = new Random();
		String r=(String) o;
		
		//（5） File cannot find exception ： java.io.FileNotFoundException
		FileReader f=new FileReader("d:/123.txt");
		
		
	}
}

---

summary