Java Thread Programming-thread Introduction

Overview

When you browse a webpage, you can read and scroll the text in the webpage while waiting to load the image. Is this a bad way? In the word processing software, when you open another document to be edited, how can you print a document in the background? You may have enjoyed the benefits of replying to an email and downloading large file attachments. By allowing a multi-threadProgramMultiple tasks at the same time can make these convenient functions possible. This book helps you learn these necessary skills and combine this useful feature with your Java program.

What is a thread)

When a modern operating system wants to start running a program, it first creates a process ). A process is a program currently being executed. Each process has at least one running thread ). Sometimes, a thread is considered a lightweight process ). A thread is a programCodeThe execution path (a path of code execution). Each thread has its own local variables, program counters (pointing to commands being executed), and lifecycles. Many modern operating systems allow multiple threads to run simultaneously in one processor. After the JVM (Java Virtual Machine) is started, a new process is created. Many threads can be created in this process.

Generally, the execution of Java code starts from the main () method, and then processes the code along the program path until all the statements in the Main () method are completed. This is an example of a single thread. This "Main" thread is created by JVM, and then the thread starts to execute the main () method, execute all statements in main (), and finally after main () is completed, this thread will die ).

The second thread that is always running in JVM is the garbage collection thread (garbage collection thread ). This thread clears all discarded objects and recycles their memory. Therefore, even a simple Java program that outputs "Hello World" to system. Out is running in a multi-threaded environment. There are two threads, one is the main thread and the other is the garbage collection thread.

When a Java program contains a graphical user interface (GUI), JVM automatically starts multiple threads. One thread is responsible for passing GUI events to corresponding methods in the program, and the other thread is responsible for drawing GUI windows.

For example, a main thread based on a GUI program is responsible for a complex and long-time computing. When the computing is in progress, the user clicks the "Stop computing" button. At this time, the GUI event thread calls the event processing code written for this button to terminate the computing thread. Imagine that if there is only one thread, the two (computing and termination calculation) cannot be performed simultaneously, and it will be difficult to interrupt the calculation.