Java-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.