Java fundamentals (should be understood by the Java Engineer Primer)

1) building a Java development environment

2) Understanding Java features (features)

3) Understanding The functionality of Java virtual machine software

4) Describe garbage collection concepts

5) Enumeration implements the Java code security Method

6) encoding compile run jaav application

1.JDK(JAVA SDK):JVM ( runtime ) API(class collection programming documentation), and some development tools

includes Java virtual machine (JVM): Compiling and executing java Programs (cross-platform)

JDK class Library (API): Contains various java classes and Practical classes:java.long,java.io, classes in java.util,javax.swing,java.sql , etc. are located in the JDK the class library.

Development tools:javac compiler tool;

Java runtime tools;

Javadoc Tools for generating Javadoc Documents

Jar Packaging Tool

2.jvm:java virture Machine, simulates the Java operating environment virtual out of the CPU (supports java Cross-platform)

3.JAVA non-cross platform and bytecode bytecode cross-platform bytecode bytecode belongs to the intermediate code

A) and Java -related environment variables There are those few, what do they do?

Java_home: Simplifies content input during other variable settings.                          You can define the installation path of the JDK as a variable and replace it with this variable in the future wherever you use the JDK installation path.

Path: Specifies the path range to find the corresponding executable when executing the external command.

CLASSPATH: represents the root path of the Java class, andthe Java command looks for the desired Java class from the CLASSPATH ; When the Java compiler compiles java classes, it also looks for the required Java from the CLASSPATH The default value for Classpath is the current path.

B) Java 's excellent features

Cross-platform: bytecode across platforms, byte codes are the same on any platform, but different platforms have different platforms Jvm

Easy programming: No pointers (garbage collector), object-oriented (in line with human thinking)

Code security: Byte-code checker for network transmission

C) Code Checker specification

1) does the code meet Java specification requirements

2) Code does not compromise the security of the system

3) no stack overflow on overflow or underflow

4) Checking of parameter types

5) type conversion Check types can be converted to each other

overflow and underflow of the stack :

Overflow: is when an extra-long data enters the buffer, the excess is written to the upper buffer, the upper buffer may be the data, the pointer to the previous instruction, or the output of other programs, the content is overwritten or destroyed. A small amount of data or an overflow of a set of instructions can cause a program or operating system to crash.
Underflow: When an extra-long data enters the buffer, the excess is written to the lower buffer, the lower buffer holds a pointer to the next instruction, or is the output of another program.

4.Garbage Collection Management memory ( automatically frees up space processing memory ) system-level threading

New--> New Object--> Create memory space, request memory space

5.JIT:just in time compiler converts Java bytecode into a program run directly by Java

6.Package A package can contain multiple java classes to manage a set of Java classes that correspond to directories in the file system

1) Resolve name conflict issues

2) Easy class Management

full-Limit naming of classes: Package name + class name

Cp: Mount Path

Import Imports date Gets the current time

7.public source file can only have one Public common class name and file name consistent

8.Javac Java source files compiled into a class file can compile multiple files at a time

9.Java program starts from main method

10.Java There can be more than one Java class in a source file . However, there can be only one Multiple source file that is public and may create multiple public

Class

11.API: Application Programming Interface Class Library

default value of 12.java.lang package

javac-d(Create directory automatically)classes Src/hello.java

JAVA-CP ( Mount Path ) classes Com.briup.chap01.hello

Java fundamentals (should be understood by the Java Engineer Primer)