scholl concepts

1.java 3 Large features encapsulation, inheritance, polymorphism. Encapsulation: Tag your instance variable as private (private), and provide public getter and setter to control access action, in fact, data hiding. Polymorphism: Three elements of polymorphism, inheritance, override, parent class reference to child class object. The reason to achieve polymorphism is to do before the words die, an object has multiple faces, blurred a little imagination space, concrete time to materiali

"value=". For example, the above method Getfruit () suppresswarnings annotation is abbreviated.Simple description of common parameter values for suppresswarnings annotations:1.deprecation: Warning when using a class or method that is not in favor of use;2.unchecked: Warning When an unchecked conversion was performed, such as when using a collection without generics (generics) to specify the type of collection to save;3.fallthrough: A warning when a Switch block directly leads to the next situat

① array pointers and arrays of pointers1. The array pointer is used to point to an array whose name is the address of the first element of the array (the array name is a pointer to the first element of the element type and points to the beginning, such as int array[5], and the array is a pointer to array[0] and the type is int*)int testarray[5] = {12345}; int (*ptestarray) [5] = Testarray; int *ptest = Testarray;2. The pointer array is a normal array in which each element of the array is a point

forcing parsing. However, variables that are implicitly parsed must have a value (non-nil) on each access, or a run-time error will occurLet possiblestring:string? ="a possible string"Let forcedstring= possiblestring!//must be added! For forced parsingLet assumingstring:string! ="An implicitly unwrapped optional string."Let implicitstring= Assumingstring//no need! For forced parsing//Note: If a variable may be nil, it should always be set to optional, rather than an implicitly resolved optional

statement that invokes the static block of the class and initializes the static member variable.when you use LoadClass to load a class, the class is not initialized by default.The class loader conforms to the principle of the parent delegation, and the custom ClassLoader, why can I load class?Custom ClassLoader, you can override loadclass non-compliance with the parent delegation principle. In addition, some class files are not visible to the class loader of the system, or the system's ClassLoa

availability of up to 99.999%, thus making the server less than 6 minutes of downtime per year.3, high scalability, without affecting the existing services, we can upgrade the system, expansion or various maintenance operations and so on. Because the cluster is composed of multiple servers, it supports a large number of CPUs, its ability to carry out a clear advantage.4, high resource utilization, in large enterprises, due to the elimination of the old host more, so they can be connected with t

All the data in Linux is stored in files, stored in the directory, and the directory is tree-like.(i) File type1. Common FilesIncludes text files, source code files, executables, and so on. There is no distinction between text and binary files in Linux.2. CatalogueSimilar to the directory folder in Windows.3. Device filesCharacter device file: A file that begins with "C" and transmits data directly.Block device file: A file that begins with "B" and reads and writes data blocks with memory buffer

called. The Static member functions do not has a this pointer. U Using ' declaration? 　 A using declaration makes it possible to use a name from a namespace without the scope operator. V Virtual non-virtual function Run-timeCompile time The behavior of a non-virtual function is known at compile time and the behavior of a virtual function is not known Unti L The run time. 　 virtual function Derived classRedefined

1.bool Variables and operationsPrint 1 + 1 = = 2Print 1 + 1! = 2Print 1 + 1 = = 2 and 1 + 1 = = 3Print 1 + 1 = = 2 or 1 + 1 = = 3Print not 1 + 1 = = 2print 1 in [1, 2, 3]Output:TrueFalseFalseTrueFalseTrue2.ifLight = "Red"if light = = "Red":print "stop!"elif Light = = "Green":print "go!"elif Light = = "Yellow":print "Slow down!"3.whileA =While aa = a +1Print a4. for inContact = {"Li Lei": "1303030", "Hanmeimei": "1450303"}for i in Contact: print I, Contact[i]Output:"Li Lei": "1303030""Hanmeime

parameter does not change the corresponding value in the arguments, and the length of the arguments object is determined by the number of arguments passed in, not by the number of named arguments defined by the function, if only one parameter is passed, then arguments[1] The value set will not be reflected in the named parameter. In strict mode, assignment to arguments becomes invalid, and second, overriding arguments can result in syntax errors By checking the type and number of in

Equals () method, it is the same object for the class file, String, date, and wrapper class (Wrapper Class) to compare types and contents regardless of the reference;Cause: The Equals () method is overridden in these classes to compare whether the content is the same.So although it's not the same object here, the Equals () method still returns TrueBecause both string and string2 are complex data types, their memory is allocated in the heap,The data stored in the heap can be duplicated, so the s

ClassificationFirst, according to whether the data related to internal and external storage exchange1-Internal sorting: For small files with not many records2-External sort: Large file with too many records to put all the records into memory at one timeSecond, according to the strategy to divide the internal sorting method1-Insert Sort: Direct insert sort with Hill sort2-Select sort: direct selection sorting and heap sorting3-Exchange sort: bubble sort and quick sort4-merge sort5-Assigning sortA

maximum of 2k-1 nodes (k≥1).Property 3 In any-tree binary tree, if the number of terminal nodes is N0, the degree of 2 of the node is N2, then no=n2+1.Property 4 The depth of a complete binary tree with N nodes isProperty 5 If the nodes of a complete binary tree with n nodes are numbered in sequence, any node I (1 2i> N, the node I have no left child, otherwise its left child is node 2i;3 if 2i+1>n, then node I no right child, otherwise the right child is node 2i+1;Java Data Structure Series--T

characteristics of the learning, so that the classification is not allowed, for example, a special feature as a category of judging criteria, so that does not have a particular attribute of the data into this category. This is called fitting, English is called overfitting literal translation is over-matching, that is, matching is too thin, a bit too. To solve this problem, it is necessary to simplify the decision tree, to remove some of the characteristics too refined, the reaction in the tree

Sorting is an important operation of data structure.Sections 5.1 through 5.6 of this chapter describe the various methods of ordering within, and 5.7 sections describe the methods of sorting out.In addition, heap ordering is a typical sort of selection, and the algorithm for heap sequencing is described in chapter 8th.5.1 Basic ConceptsBefore discussing the concept of sorting, first introduce the concept of sort code.A sort code is one or more fields in a node whose values are used as the basis

difficult to understand, so will be updated in the follow-up experiment text, really hope to help everyone, thank you!Classification of logs:Kernel and system logs, user logs, program logsLog Save location:Default in:/var/log directoryKernel and public message log:/var/log/messagesScheduled Task log:/var/log/cronLog message Importance:0 Emerg (Emergency): causes the host system to become unusable1 alert (warning): A problem that must be taken immediate action to resolve2 Crit (severe): more ser

-related configuration files:/etc/groupB, group-related commands: Groupadd-g (create Group), Groupdel (delete group), gpasswd (add user to Group)GPASSWD command:Format: GPASSWD (option) group account name-A: Adding a user to a group-D: Delete a user member from within a group-M: Defines a list of group members, separated by commas (additional groups)Add:A, id commandPurpose: Query user identification (ID user name)B, Groups commandPurpose: Query the group to which the user belongsGroups user Nam

Expiration TimeNegative Answer TTLCache DNS Server: Cache only, no authoritative answerForwarders: Not cached, forward onlyA resource record RR (Resorce record) is placed inside the zone dataFormat of RR:TTL can be omitted when the complete definition isName TTL in RRT VALUEWww.baidu.com. In A 1.1.1.11.1.1.1 in PTR www.baidu.com.Resource record type: (RRT)SOA (Start of authority) indicates when the master and slave servers in the zone are synchronized, enabling the authorization serverZone_name

commandls -a| grep VimFile permissionschmodFind--regexp regular expression, support regular expression in Ubuntu Note: Locale does not directly look up files in the system (nonsense, otherwise it cannot be so fast), but instead reads a database (maintained by the system). Therefore, for a file that has just changed, it may not be found. UpdateDB is basically performed once a day. The remedy is to run the updatedb manually once, run find with sudo permissions to Find the contents of the specif

10Nb_get_retry 3Delay_before_retry 3Connect_port 8888}}Real_server 192.168.1.107 8888 {#指定real_server2的ip地址Weight 3 #配置节点权重Tcp_check {Connect_timeout 10Nb_get_retry 3Delay_before_retry 3Connect_port 8888}}}Save Exit,Open keepalived ServiceService keepalived StartView status Ipvsadm-l-NConfigure LVS from the server (another LVS)Apt-get Install keepalivedThe configuration from the server is roughly the same as the primary server, to change the state from master to backup in keepalived.confChange