Shulou(Shulou.com)06/02 Report--

This article mainly explains "how to realize TCP peer-to-peer and UDP broadcasting". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to achieve TCP peer-to-peer and UDP broadcasting".

System:

A large number of static methods are provided in the System class to obtain system-related information or system-level operations. In the API documents of the System class, the common methods are:

-public static long currentTimeMillis (): returns the current time in milliseconds.

-public static void arraycopy (Object src, int srcPos, Object dest, int destPos, int length): copies the data specified in the array to another array.

-public class Demo11SystemArrayCopy {

Public static void main (String [] args) {

Int [] src = new int [] {1pm 2pm 3pm 4pm 5}

Int [] dest = new int [] {6 record7, 8, 9, 10}

System.arraycopy (src, 0, dest, 0,3)

/ * after the code runs: the elements in the two arrays have changed

Src array elements [1, 2, 3, 4, 5]

Dest array elements [1, 2, 3, 9, 10]

, /

}

}

Date

Java.util year, month, day, hour and second

Java.sql year, month, day

Automatic conversion from database to java

Java conversion database cast

String

* * immutable string * *

String S1 = "123asf5af"

Variable string

StringBuffer s Buffer = new StringBuffer ()

Mutable and immutable, what you see is that the string is immutable.

= = compare with equals string with equals = = address equals content

* * the equals method of Object is overridden by default using equals**: String, and the comparison rule is reformulated so that the address of S1 and S3 attribute is compared.

Demo2 replacement

Trim removes the spaces on both sides of the string.

Dictionary sort

* * StringBuilder** (thread security is not considered after JDK1.5)

Past single character: converted to byte array

Web site

URL: protocol + domain name (IP address) + port + path of resource on server + query condition

The function of the URL: to realize the communication between client and server

Protocol: is to specify a traditional specification

Domain name / IP: marking the only host on the network can be simplified to write: baidu

Port number: Mark a server on the same host [0Pol 65536]-can be saved. Default is 80.

Can be omitted: resource path, query condition

Array

The length of the collection turned around by the array is immutable.

Regular expression

1. Regular expression: defines the composition rules of a string.

1. Single character: []

For example, [a] [ab] [a-zA-Z0-9] [5,6]

\ * A single character with a special symbol that represents a special meaning:

\ d: single numeric character [0-9]

\ w: single word character [a-zA-Z0-9 _]

two。 Quantifier symbol:

?: indicates 0 or 1 occurrence

*: indicates 0 or more occurrences

+: appear one or more times

{mdirection n}: stands for m

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