Java Basics-Class

1. Related concepts of the class:

• The class name must be the same as the file name when there is a public adornment

• If there is no public keyword decoration, it can be different

• A class is an abstraction of something with the same characteristics and behavior.

• Features can be understood as static

• Behavior can be understood as dynamic

• *package the current file into the corresponding package

• *package behind usually write URLs upside down

• *package must be the first line of the current file

• *import introduce the classes that you need to use in this file

2. Variables define three elements:

* Type modifier variable name = initial value; * Variables created using a class can be called Object * Class Name Object name = new class name ();

3. Properties of the Action object

* Object name. property name to modify it

* Object name. Method name to modify it

4. Method: The behavior of the class is the method

* The method is written as follows: * Modifier return value type method name (parameter list) {}

4.1 Modifiers:

* There are three types of modifiers that can be written: * Public Private protected * not written as default

4.2 Return value type

* No return value type: void * has return value: int  double String Car ... * return value needs to use Return statement within method  * No return value type can also use return to stop the current method

4.3 Depending on the return value and parameters, there are four methods

* 1. No parameter no return * 2. No parameter is returned: A method with a return value can be understood as an expression, and the result is the return value of the method * 3. There is no return: The parameter method needs to be declared according to the method, pass in the corresponding parameter * * * parameters passed in Parameter type * * method declaration is called parameter * method * 4. There is a parameter return: The passed argument has no parameter type

5. Methods can be called in the method

* Method Overloading: * Method name is the same, but parameter list is different: number-order-type Different *---------method overload and return value type Independent---------

6.setter methods and Getter methods

* Setter Method: Setup * Format: public void Set Property name () * Getter method: Accessor * Format: Public property type Get property name () * Setter and getter method is not required to write * as required to determine whether the property needs to be set The device or accessor * set and accessor are not required to appear in pairs * This represents the object of this class * this. Property---Represents the property of the class, not the parameter

Construction Method:

* Initialization when creating an object * when there is no constructor method in the class, the compiler creates an parameterless constructor method * In the format: Access modifier class name (parameter list) {} * constructor method can also overload * constructor method cannot have a declaration of a return value type

7. Set directly within the construction method

* ****** do not use return within the constructor method to return a value ****** * as long as there is any one constructor method in the class * The compiler will not generate an argument-less construction method

8. Inheritance

*  new classes derived from existing classes *  keywords are: extends *  only single inheritance is allowed in Java

9.super ()

* SUPER () represents the constructor method that calls the parent class * super () must be written in the first row of the method * First assign the properties of the parent class integrated * before assigning the properties of the class to the value

10.final decorated class, which means that the class cannot be inherited

• The final modification method, which means that the method cannot be overridden by a quilt class

• Final decorated property, which means that the property can no longer be assigned a value

• ---The final decorated property, the variable is named plain uppercase---

Common classes

1.String class

     * (1). String comparison method:     * The return value type is Boolean and the argument is another string     * object. Equals (Object)

     * (2). How to find a String 1 indexOf (parameter)

     * The return value is int, which is the index of the character in the string

     * Returns the first qualifying character position, no return-1

     * Parameters are characters that need to be searched

     * Find Method 2 indexOf (parameter 1, parameter 2)

     * Parameter 2 is the location to start the search, and the incoming position will be judged

* Returns the position of the first character that meets the requirement from the start position, no return-1

     * (3). String substitution method IndexOf (parameter 1, parameter 2)     * The return value is the new string after substitution     * Parameter 1 is the substituted character (string), parameter 2 is the substituted character (string)     * If the parameter 1 does not exist in the original string, it does not replace     * Replace all parameters in the original string 1
* (4). Determines whether a string starts with the specified string Startwith ()

* Return value type is Boolean

     * Parameters are strings that need to be judged

* (5). Determine if a string has been specified at the end of the string EndsWith () 

* Return value type is Boolean

     * Parameters are strings that need to be judged

    * (6). Remove the space at the beginning and end of the string    * TRIM ()    * method for calculating the length of a string long  ()    * return value int

2.StringBuffer

* Modifiable String Classes

     * (1). How to intercept strings substring ()     * Parameter 1 is the index from which to start     * Parameter 2 is the end of the index     * Tips: Follow the left closed right open principle [)     * (2). Delete method of string delete ()     * Parameter 1 is the index from which to start deleting     * parameter 2 to which index end delete
　   
     
     
     * Tips: Left closed or present
Class Set Framework

1. Arrays: Collections of the same data type

* Elements in the array are ordered * format: Data type array name [] = new data type [array length]; * Use elements in an array:     * Value or assignment by array name [element position]

Common methods of 2.ArrayList

  * ArrayList can be understood as inheriting collection  * Collection All methods ArrayList can be used (1) to create a ArrayList class  * arraylist<string> list= new Arraylist<string> ();  * <> Middle type is called generics      * temporarily understand array stored element type     (2) Add Method List.add ()      * add element List.add at specified position (parameter 1, parameter 2)      * Parameter 1 is position      * Parameter 2 for Add content (3) Get Method List.get ()     (4) Delete method List.remove () (     5) Replace method List.set (parameter 1, parameter 2)      * Parameter 1 represents the location to be replaced     * Parameter 2 for the new element    (6) Gets the position of the specified element in the collection List.indexof (parameter)     * Returns a numeric value of type int

3.MAP is a data structure for storing key-value pairs

* Map Storage data is unordered (1) Create a Map object  * hashmap<string,string> map= new hashmap<> (); (2) Add method Map.put (parameter 1, parameter 2) * need to pass in two parameters * The first parameter is key * The second parameter is value (3) Remove Method Map.Remove () * Removes the entire key value pair (4) based on the key value to  determine if a key or Valu is included E   1> Map.containskey (key value) if (Map.containskey ("Leopard Head")) {System.out.println ("the collection contains the Leopard Head");} Else{system.out.println ("No leopard head in the collection");   2>map.containsvalue (value value) if (Map.containsvalue ("Lu Junyi")) {System.out.println ("contains Lu Junyi in the Collection");} Else{system.out.println ("The collection does not contain Lu Junyi");}


IO Stream and exception

1. Exception: The error that caused the program to break

* Exceptions can be classified as run-time exceptions and non-runtime exceptions * Exceptions need to be handled, otherwise the program will be interrupted

2. Exception handling

* Method: Try...catch * Write the statement in the try block with the possibility of an exception * If an exception is thrown in a try, the catch can be caught in the capture to write multiple, but note: * If an exception has an inheritance relationship, you need to write the parent class behind the subclass. * Note: either No exception occurs and finally blocks are executed to

3.throws keywords

* Used on a method declaration, which means that calling the method may throw an exception * depending on the classification of the exception, decide whether to force the call to use try: catch* if the thrown exception is a run-time exception, the try...catch* is not enforced if the exception thrown is a non-runtime exception, forcing Try...catch

4.throw keywords

* Throws an exception in a method * Determines whether to add throws* in a method declaration if the exception thrown is a non-runtime exception * You need to use the throws declaration in a method declaration

5. How the byte stream is used

* Reference to create input stream and output stream  file src = new file ("/users/dllo/desktop/io/src.txt");  File Dest = new file ("/users/dllo/desktop/io/dest.txt");  FileInputStream  fis = new FileInputStream (SRC);  FileOutputStream fos = new FileOutputStream (dest);

6. How character streams are used

* Create references for input stream and output stream

File Src1 = new file ("/users/dllo/desktop/io/src1.txt");

File Dest1 = new file ("/users/dllo/desktop/io/dest1.txt");

FileReader FR = new FileReader (SRC1);

FileWriter FW = new FileWriter (DEST1);

Java Basics-Class