what is java thread

What is a java thread

Thread in Java refers to a member of the java.lang.Thread class The execution of an instance or thread. Use the java.lang.Thread or java.lang.Runnable interface to write code to define, instantiate, and start new threads.

1, Process

A process refers to an application running in memory. Each process has its own independent block. Memory space, multiple threads can be started in one process. For example, in Windows systems, a running exe is a process.

2. Thread

A thread refers to an execution process in a process. A process can run multiple threads. For example, the java.exe process can run many threads. Threads always enter a process, and multiple threads in a process share the process's memory.

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3. Java’s threading model

Since Java is a pure object-oriented language, , Java's threading model is also object-oriented. Java encapsulates all the necessary functions of threads through the Thread class. To create a thread, there must be a thread execution function. This thread execution function corresponds to the run method of the Thread class. The Thread class also has a start method, which is responsible for establishing a thread, which is equivalent to calling the Windows thread creation function CreateThread. When the start method is called, if the thread is successfully established, the run method of the Thread class is automatically called. Therefore, any Java class that inherits Thread can create a thread through the start method of the Thread class. If you want to run your own thread execution function, you must override the run method of the Thread class.

In addition to the Thread class in the Java thread model, there is also an interface Runnable that identifies whether a Java class can be used as a thread class. This interface has only one abstract method run, which is the thread execution function of the Java thread model. . Therefore, the only criterion for a thread class is whether the class implements the run method of the Runnable interface. In other words, a class with a thread execution function is a thread class.

As can be seen from the above, there are two ways to create a thread in Java, one is inheriting the Thread class, and the other is implementing the Runnable interface, and Threads are created through Thread and classes that implement Runnable. In fact, these two methods are essentially the same method, that is, they both create threads through the Thread class and run the run method. But their big difference is that threads are created by inheriting the Thread class. Although it is easier to implement, since Java does not support multiple inheritance, if this thread class inherits Thread, it cannot inherit other classes. Therefore, The Java threading model provides methods to establish threads by implementing the Runnable interface, so that thread classes can inherit business-related classes instead of the Thread class when necessary.

● All programs written in Java run in the Java Virtual Machine (JVM). Within the JVM, the multitasking of the program is implemented through threads. Every time a java application is started with the java command, a JVM process will be started. In the same JVM process, there is only one process, which is itself. In this JVM environment, all program code runs in threads.

● Generally common Java applications are single-threaded. For example, when you use the java command to run the simplest HelloWorld Java application, a JVM process is started. The JVM finds the entry point of the program, main(), and then runs the main() method, thus creating a thread. This The thread is called the main thread. When the main method ends, the main thread is completed. The JVM process also exits immediately.

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