Summary of Java Fundamentals (i)

Le Orange Valley Java Summary-java Introduction

(1) Java architecture: j2se,javaweb,j2ee

(2) java features: platform-independent (virtual machine), garbage collection (makes java more Stable)

(3) JDK and Jre,jdk:java development environment, Jre:java Operating environment

(4) First Java program: Helloworld,java's entry is main (public static void main (string[] ARGS))

(5) Java Program Development steps:. Java compilation (javac) into A. Class run (java). class file

Happy Orange Valley Java Summary-basic data types

Marker: the place where you can take a name is called a marker

Rules for Markers:

1, can only be letters, numbers, underscores, $; cannot start with a number; strictly case-sensitive; cannot use keywords as markers

2, keyword: keywords are all lowercase

3, constants: such as 123, "hello"

*也可以使用final定义常量（请参照Math.PI），如public static final int SLOW_SPEED=1;

4, variable: The essence of a variable is a small area in memory that holds the data in this area

*变量申明：类型变量名字*变量必须先声明，再赋值，再使用*注意区分基本数据类型的变量与引用数据类型的变量*变量的作用域，局部变量与成员变量：变量在哪个大括号里定义，就在哪里有效，出了大括号无效

5, Basic Data type: Java data types fall into two main categories: basic data types, Reference data types

* Basic data types are divided into4Class8boolean,char,byte,short,int ,long,float double*boolean type only Span class= "kwd" >true,false* char is unicode coded *float,double Be accurate (not absolutely Exact)                

6, conversions between basic data types

*123Literal constants areIntType12.3Literal constants areDoubleType8888888888888This literal constant has a problem (because it has exceededIntThe scope of the change to8888888888888L）*BooleanIncompatible with other types*Byte,Short,charint * The small-capacity data type can be automatically converted to a high-capacity data type: byte< Span class= "pun" >,short,char-->int-->long-->float< Span class= "pun" >-->double* Bulk conversion to small capacity data type for casting * A variety of data types to perform operations, first convert to the largest data type and then perform operations, the type of the entire expression is the largest data type * must master the exercises on ppt 
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Summary of Java Basics (i)