MyEclipse Java Basics Using notes

First, the Java development platform

Javase standard Java application Application Gobang, calculator, QQ

Java EE Enterprise Linux Enterprise application

Javame Mini-Device Android replaces

Second, Java terminology

JDK Java Development Kit

JRE Java Runtime Environment

JVM Java Virtual machine

GC Java Memory object garbage collection mechanism automatic lazy lazy recovery

API application programming interface corresponding to Javadoc documentation

Java.lang.string class String Class

Java.lang.System class System Class

IDE Integrated Development Environment MyEclipse8.5 (the higher the version, the more memory)

Third, Java programming steps

1. Download and install the JDK

2. Configure the system environment variables

Installation path for Java_home JDK

Search path of the path command javac java command

Search path for the CLASSPATH class

Can be used repeatedly on the command line after configuration (only configuration in sequence.

3. Editing

4. Compile Javac hello.java->hello.class start compiler

5. Run Java Hello to start the virtual machine

Iv. Java Annotations Comment

Code and Documentation (note) are equally important

1) Single-line comment//

2) Multi-line Comment/* * *

3) Document Comment/** */

V. variables

Variable name corresponds to the value of the variable, with the data type

Declaring a variable for the first time must explicitly specify the data type

String name = "Zhang San Fung";

Name = "Zhang San";

int high = 180;

High= 190;

Project, describe the project size: 30 people/month

30 people * 1 months

1 People *30 Month

5 people *6 Month

On average no one writes 10 classes a day, one months and 20 days;

Altogether: 5*10*20*6=6000 class *.class

Use of MyEclipse

Java Package Keyword Packages

1, meaning:

Package is like the usual directory, a layer of packages corresponding to a layer of directory structure, the benefits of subcontracting: the ability to classify. Class management.

Create a new text document under D:\

2. Grammar

Valid position in the first line of the source code:

Package name;

Specification of package name: All lowercase, used between multiple packages. Separated

Once you have a package name for your class, you need to use the full name (fully qualified name) package name. Class Name

Package day01;

The package hierarchy in the project is deep:

Package company domain name. The name of the project. Module name. sub-module name;

Example 1, Souhu Java first day of code: Package Com.sohu.javase.day01;//com.sohu is the domain name

Code for the next day: Package com.sohu.javase.day02;

Package com.sohu.javase.day01;

Class hello{//classes name Com.sohu.javase.day01.Hello

}

Example 2, IBM Company, employee Management system EMS, employee class EMP

Package com.ibm.ems.entity;//Entity Pack

Class emp{//classes name is COM.IBM.EMS.ENTITY.EMP

}

Example 3, Www.bypp.com.cms

Package com.bypp.cms.entity;

Class duck{

}

Example 4,

The declaration of a package can only be in the first row of the source code valid location
Package day01;
public class hello{
public static void Main (string[] args) {
System.out.println ("Hello");
}
}

Compile: D:\ javac-d. Hello.java

-D has two meanings:

1) make the compiled. The path to the class file. Current directory

2) If we specify a package, the level of the package will be automatically generated with the corresponding directory results

Running: Java Com.day01.Hello

Implementing Myinfo.java with MyEclipse

Tips for using the IDE:

1) Select Workspace

2) New Java Engineering (Java Project Java projects)

In the table of contents are:

SRC directory sourse source code file directory *.java

Bin directory binary byte-code file directory *.class

3) Create a new class under SRC

Click: File->new, class;

Package Name: DAY01;

Class Name: Hello

4) Edit Font

5) Finish editing

6) Compile save immediately compile Ctrl + s

If the compilation passes, there is no red underline;

If the compilation error occurs, the red underline appears;

Syntax error, insert ";" To complete blockstatements

7) Run

Right-click Java Application, Run as, source code

Note: ALT +/Quick prompt and generate fixed code

Main Master method

SYSO system output

Second, identifier identifier

Identifiers are used to represent the various names of code: package Name, class name, method name, variable name, constant name, and so on.

1, the identifier rules 5 must abide by, or compile error;

(1) must consist of letters, numbers, underscores, &, the first letter cannot be a number;

Letter: A-Z to 52;

Number: 0-9 10;

(2) cannot be a Java keyword; 50 + 3 self-par value

Keyword Features: all lowercase class, int, double, static, public ...

Literal value: True, False, NULL

(3) Case sensitivity (case sensitive)

String vs. string, int and int

(4) No limit on length

ArrayIndexOutOfBoundsException

(5) Support Chinese, but not recommended

int age = 23;

Problem:

2. Specification of identifiers 5 business habits

(1) class name, interface name each word the first letter name ;

(2) variable name, method name each word first letter lowercase , followed by the first letter of each word capitalized ;

(3) package name all lowercase , between package names. Separated

(4) The constants are all capitalized , the words are separated by _;

(5) See the meaning of the name

Name N1

Age A1

Arrayindexoutofboundexception Array decimal Bounds exception

Third, the Java keyword key words

Different features are represented in the language, all lowercase.

Exercise: Prompt from the console and enter name and age, and output

Package Name: Day02, class Name: Testtestscanner provides the Main method

Need to use a class: Java.util.scaner class, Scanner class

Java.util Package Kit Utilits (tool)

Created an object for the scanner class SC

Scanner SC = new scanner (system.in);

String name = Sc.next (); Enter string data to invoke the next () method of the Scanner object

Features: is a blocking method, waiting for the user's input, know that the user entered the data, the results returned before continuing to execute

Specific steps:

1, create the object of scanning class;

2, print "Please enter the name";

3, input anme;

4. Print "Please enter Age";

5, enter age;

6. Print out name and age;

Attention:

Using scanner, import statements are required

The import statement is used to declare the package under which the class is used.

The following do not have to write the import statement:

1) The class under the same package does not need import direct use;

2) The class under the Java.lang package does not need to be directly used by import;

3) Lang Packet Language language pack is too common, m default direct use

For example: Java.lang.String class, String class

Java.lang.System class, System class

Java.lang.Math class, Arithmetic class

Note: Import java.util.*; indicates that all classes under the Java.util package can be used, but not child packages (just one layer)

* is a wildcard, the proposed project requires a specific class name, high efficiency

The JDK provides a rich range of APIs (classes and interfaces) that are rich in functionality and are managed through different packages:

Java.lang.String class, String class

Java.lang.System class, System class

Java.lang.Math class, Arithmetic class

Java.util.Scanner class Scan Class

Corresponds to a document: Javadoc document/API document, is an HTML page format document.

Iv. data Types for Java

1, computer expression number: binary, every two into one, can represent 2^4=16 species,

2. Java representation number: positive, negative, and 0

The complement of the binary number is new, using the highest bit as the sign bit (leftmost)--0 is positive, 1 is negative

Positive complement: Is the original code, negative complement: the corresponding positive number of the original code, according to the position counter +1;

4-bit twos complement: capable of representing 2^4=16 species, indicating number ranges: -8-7,-2^3-2^3-1

8-bit twos complement: can represent 2^8=256 species, indicating number range: -128-127,-2^7-2^7-1;

01111111--127 1+2+4+8+16+32+64=127

......

00000000--0

11111111--( -1) 00000000+1=00000001-> 1->-1

......

10000000 ——-128

1) Known 8-bit binary complement 11111111, translated into decimal number, because the highest bit is 1, negative number, (bitwise negation + 1)

Example: 11111111 translated into decimal number, 00000000 + 1-> 00000001-> 1->-1;

2) Known decimal number-1 is converted to the complement of 8-bit binary number: (1 of the original code bitwise INVERSE + 1)

bitwise inversion with 1 binary digits + 1:00000001-> 11111110 + 1-> 11111111 (-1 complement)

4. Characteristics of Java data types

Java is a strongly typed language that declares a variable for the first time, must explicitly specify the data type, declares the variable for the first time, and must explicitly specify the data type.

Java syntax is more rigorous, secure, and prescriptive.

String name = "Tli"; String literals

Name = "Lili";

name = 123; Integer numeric value, type incompatible, compilation cannot pass

JavaScript is a weakly typed language:

var n1 = "Tli";

N1 = 123;

5. Classification of Java data Types (important)

(1) basic type , also known as simple type, native type (prime) 8 kinds

byte short int long char float double Boolean

Byte short integer integer Long integer character single-precision floating-point double-precision floating-point Boolean

Capable of representing data: byte short int long char float double;

Capable of representing integers: byte short int long char;

Ability to represent decimals: float double;

Capable of representing Boolean: Boolean (True, false);

Ability to represent characters: char;

Commonly used: int long double char Boolean;

Underlying storage: in bytes byte as unit, press bits to store.

(2) A reference data type, also known as a complex type, an object type of countless kinds, class can be continuously defined

Underlying storage: Reference (object memory address)--memory object (key-room--Thing)

It is divided into 5 types according to the form of expression:

Classes class Interface interface array string[]/int[] Enum callout

(3)void no return value type

Note: You cannot use a variable to define it, only the return value type of the method, which means that no results are returned.

public static void Main (string[] args) {...}

public void PlayGame () {...}

Exercises: Write Java program: Testempscanner.java

Prompt from the console and enter basic information about the employee and output all information at once in the console.

Name of employee, employee age, employee salary salary

Tip: You need to use the scanner class Java.util.Scanner

Thinking: The thought of process-oriented programming

Steps:

1. Creating the Scanner Object SC

2. Prompt and enter name

Main outline: Java programming steps

1, the command line development method

(1) Editing Java source program Hello.java

Plain text editor, such as Notepad, EditPlus, etc.

Package day01;

public class hello{}

(2) Compile javac-d. Hello.java

-->\day01\hello.class

(3) Run Java day01. Hello

2. Using IDE MyEclipse to improve development efficiency

(1) Edit

New class

(2) compiling

(3) Right-click the source code run As->java application

Second, Java annotations

Iii. identifiers: For JDK or programmer to name features in code

1 bytes = 82 binary 1byte = 8bit

Iv. keyword key words

Keywords all lowercase, indicating different functions

V. Java data types

In real life, the number of decimal digits; the number of binary digits in the computer; 16 binary, octal number is for the programmer more convenient to represent the binary number; Java uses the complement form of the binary number (the positive complement is the original code, negative number of the original code is the original code of its positive numbers to reverse + 1)

-5 of 8 is binary complement: 0000 0101-> 1111 1010 +1 = 1111 1011

MyEclipse Java Basics Using notes