【读书笔记】Java线程

Java线程

第一章 线程简介

• Java术语
• 线程概述
• 为什么要使用线程
• 总结

1.1 Java Terms

• Java
  First, is the term Java itself. As you know, Java started out as a programming language, and many people today still think of Java as being simply a programming language. But Java is much more than just a programming language: it's also an API specification and a virtual machine specification. So when we say Java, we mean the entire Java platform: the programming language, its APIs, and a virtual machine specification that, taken together, define an entire programming and runtime environment.

• Virtual machine, interpreters, and browsers
  The Java virtual machine is the code that actually runs a Java program. Its purpose is to interpret the intermediate bytecodes that Java programs are compiled into; the virtual machine is sometimes called the Java interpreter. However, modern virtual machines usually compile the majority of the code they run into native instructions as the program is executing; the result is that the virtual machine does little actual interpretation of code. Browsers such as Mozilla, Netscape Navigator, Opera, and Internet Explorer all have the capability to run certain Java programs (applets). Historically, these browsers had an embedded virtual machine; today, the standard Java virtual machine runs as a plug-in to these browsers.

• Programs, applications, applets, and other code

• Concurrency and threads
  J2SE 5.0 includes a package known as the "concurrency utilities," or JSR-166. Concurrency is a broad term. It includes the ability to perform multiple tasks at the same time; we generally refer to that ability as parallelism. As we'll see throughout this book, threaded programming is about more than parallelism: it's also about simpler program design and coping with certain implementation features of the Java platform. The features of Java (including those of JSR-166) help us with these tasks as well. Concurrency also includes the ability to access data at the same time in two or more threads. These are issues of data synchronization, which is the term we use when discussing those aspects of concurrency.

1.2 About the Examples

1.3 Why Threads

One reason that threading is important in Java is that, until JDK 1.4, Java had no concept of asynchronous behavior for I/O. This meant that many of the programming techniques you've become accustomed to using in typical programs were not applicable in Java; instead, until recently, Java programmers had to use threading techniques to handle asynchronous behavior. Another reason is the graphical nature of Java; since the beginning, Java was intended to be used in browsers, and it is used widely in environments with graphical user interfaces. Programmers need to understand threads merely to be able to use the asynchronous nature of the GUI library