[In-house study session] Java basics-execution without using IDE- (2017/07/06)

0. Introduction

Target person etc.

Target person

• People who usually use Java
• People who have never used lambda expressions available from Java 8

Prerequisite knowledge

• Basic Java usage

What i want to tell

• How to run Java with commands
• Lambda expression

Reference books

"Introduction to Java -From the basics of modern style to object-oriented and practical libraries "Technical Review Co., Ltd.

table of contents

1. Java overview
2. Execute Java with commands without using IDE

1. Java overview

Java features

A programming language announced by Sun Microsystem in 1995.

• Assuming object orientation
• Platform independent. --There is no need to modify the program for each OS. --Java Virtual Machine (Java VM) Absorbs OS Dependencies
• Many users --Many excellent libraries and middleware

Diagram of Java Virtual Machine (JVM)

• SlideShare: Java Night Seminar for Java Begineers Quoted

Java 3 editions

• Java SE(Standard Edition) --Java VM, standard API, etc.
• Java EE(Enterprise Edition) --Functions required for server application development (Web services, etc.)
• Java ME(Micro Edition) --Embedded systems such as home appliances and mobile phones

Java environment

• JRE(Java Runtime Environment) --Java application execution environment. --Can execute jar files and class files.

• JDK(Java Development Kit) --Java application development environment. --Includes tools such as compiler and debugger.

• Refer to "Introduction to Java" P16-17

Java conceptual diagram

• Java Platform Standard Edition 8 Documents Quoted

2. Execute Java with commands without using IDE

Purpose of trying with commands without using IDE

• Understand what the IDE is doing --Know what you can and cannot do with the IDE --Appropriate settings can be made in the IDE

• You will be able to resolve errors that occur in the IDE

• Personal opinion

Advance preparation

• Added the JDK bin folder to the environment variable PATH.
• Enable the use of java and javac commands.

Compile and execute with [Try] command

• Compiling with the javac command produces sample \ Hello.class.

javac sample\Hello.java

sample/Hello.java

package sample;
/** Print Hello World */
public class Hello {
	public static void main(String[] args) {
		System.out.println("Hello");
	}
}

• Execute with java command

java sample.Hello 
REM ⇒ "Hello"

Java class file

A Java class file is a file (with a .class extension) that contains Java bytecode that can be executed on the Java Virtual Machine (JVM).

• [Wikipedia: Java class file](https://ja.wikipedia.org/wiki/Java%E3%82%AF%E3%83%A9%E3%82%B9%E3%83%95%E3%82 % A1% E3% 82% A4% E3% 83% AB) Quote

[Try] Disassemble with javap command

javap -verbose sample\Hello

• Read Java class files with javap and hex editor java
• Oracle Reference javap Command

3. Java basic terms

Classpath

It needs to be set to refer to an external library (jar file, etc.).

The classpath is the path that the Java Runtime Environment (JRE) searches for classes and other resource files.

The class search path (class path) can be set with the -classpath option (the recommended method) when calling the JDK tools, or by setting the CLASSPATH environment variable. The -classpath option is recommended because it can be set individually for each application so that it does not affect other applications or change this value.

• Oracle reference classpath setting Quote

jar file

Abbreviation for ** J ** ava ** AR ** chive.

The> jar command is a general purpose archiving and compression tool based on the ZIP and ZLIB compression formats. However, the main purpose of the jar command is to package several Java applets and applications into a single archive.

Oracle Reference jar

[Try] Change the extension of the jar file to "zip" and confirm that it can be unzipped. [Try] Extract the jar file with the jar command.

REM -x:Deployment, -v:Detailed information output, -f:File name specification
jar -xvf sample.jar

[Supplement] Manifest file

In the jar file, there is a manifest file called META-INF / MANIFEST.MF.

Manifest-Version: 1.0
Archiver-Version: Plexus Archiver
Created-By: 1.5.0_22 (Sun Microsystems Inc.)
Built-By: hen
Build-Jdk: 1.5.0_22
Implementation-Title: Commons Lang
Implementation-Vendor: The Apache Software Foundation
Implementation-Vendor-Id: org.apache
Implementation-Version: 3.0

～ Omitted below ～

• Manifest file of commons-lang3-3.0.jar

The manifest file describes the version and the tools used to create the jar file.

• KAB-studio Manifest File

Java command options

Part of the Java Options category.

• Standard option --Supported by all Java Virtual Machine (JVM) implementations

• Non-standard option --A generic option specific to Java HotSpot virtual machines. Not guaranteed to be supported by all JVM implementations --Starts with -X

• Extended runtime options --Developer options for use in tuning specific areas of Java HotSpot virtual machine operations --Starts with -XX --The Boolean -XX option is valid with a plus sign and invalid with a minus sign. (-XX: + OptionName, -XX: -OptionName)

• Refer to Oracle Reference java

Java options I've used

• -Dproperty = value: Set the value of the system property ---Duser.language = ja, -Duser.country = JP, etc. --In Java source, you can get the value with System.getProperty ("user.language "); --Specified by JVM argument in Tomcat Configure Manager

• -Xmxsize: Specifies the maximum size (in bytes) of the memory allocation pool ---Xmx1024m: Specify 1024MB

• -XX: + UseGCLogFileRotation: Enable GC log rotation

• Reference site Java HotSpot VM Options

appendix

Java EE

• javax. * Package (some Java SE classes start with javax)
• Also included in the Tomcat library (such as servlet-api.jar)

Java version

How to check the Java command version.

 java -version
 ⇒ java version "1.8.0_131"

Updates will be available on a regular basis at Oracle. When an update occurs, the version string will also include the updated version number. In other words, in JDK 8 update 5 (JDK 8u5), the version string will be "1.8.0_5".

• Java Platform, Standard Edition 8 name and version Quoted

Java environment variables

Applications that use Java (such as Tomcat) may set environment variables such as JAVA_HOME and JAVA_OPTS.