title: Java-Introduction
date: 2023-11-01
author:
- AllenYGY
status: DONE
tags:
- NOTE
- Java
- Lec0
- Program
created: 2023-11-01T00:59
updated: 2024-05-31T01:02
publish: TrueJava-Introduction
Computer languages and Java
- Machine languages: 机器语言
- 10011110111100001111111 [Binary style]
- Low-level languages: 汇编语言
- Assembly language:
- add ax, bx [Intel x86 style]
- High-level: human-friendly languages: 高级语言
- Structured programming languages [Fortran, C, Pascal];
- C++ , a combination of structured programming & object-oriented;
- Java, pure object-oriented language;
- C#, similar to Java.
History of Java
- Developed by Sun Microsystems.
- Sun was bought by Oracle in 2010.
- 1996: Java version 1.0;
- … Java 1.1, 1.2, 1.3, 1.4;
- 2004: Java version 1.5, name changed to Java 5;
- … Java 6, 7, 8.
One new release every 6 months now: - September 2017: Java 9;
- March 2018: Java 10;
- September 2018: Java 11 (long term support);
- March 2019: Java 12
- ...
Java Architecture
Feature of Java
- Simple
- Object-oriented 面向对象
- Platform neutral 跨平台
- Robust, secure, scalable. 稳健 安全 可扩展
E.g.: programmers don’t need to care about memory allocation and release.
Compiler
- Compiler: a program that translates a high-level language program into an equivalent low-level language program.
- This translation process is called compiling.
Java Compilation Model
- Java compiler translates Java programs into byte-code, a language for the Java Virtual Machine.
- Once compiled to byte-code, a Java program can be used on any computer that has a JVM, making it very portable.
Java Virtual Machine (JVM)
- Reads “byte code” and executes it.
Garbage collection
- Manages memory automatically;
- Included in the JVM.
Java Development environment
Java Eviroment
- JRE
- Java Runtime Environment = JVM + Java libraries.
- For users to run byte-code programs on their computer.
- JDK 开发者使用
- Java Development Kit = JRE + Java compiler + other development tools.
- For developers to write Java software, create byte-code, and test it.
Java Edition
- Java Micro Edition (JavaME)
- Very small Java edition for smart cards, pages, phones, and set-top boxes.
- Subset of the standard Java libraries aimed at limited size and processing power.
- Java Standard Edition (JavaSE)
- The basic platform, which this course will cover.
- Java Enterprise Edition (JavaEE)
- For business applications, web services, mission-critical systems.
- JSP, Servlets, JDBC, EJB3.0, Struts - Spring - Hibernate.