1.启动线程代码

public class MultiThreadExample {public static void main(String[] args) {// 创建两个线程对象Thread thread1 = new Thread(new Task());Thread thread2 = new Thread(new Task());// 启动线程thread1.start();thread2.start();}
}class Task implements Runnable {@Overridepublic void run() {// 执行具体的任务逻辑for (int i = 0; i < 5; i++) {System.out.println("Thread: " + Thread.currentThread().getId() + " Count: " + i);try {Thread.sleep(1000); // 模拟耗时操作} catch (InterruptedException e) {e.printStackTrace();}}}
}

2.解析new Thread(new Task());

调用Thread
下面方法是一个公开的，其他方法都是私有的，保护了线程类方法内部的安全

   public Thread(Runnable target) {init(null, target, "Thread-" + nextThreadNum(), 0);}

调用init，方法变私有 private

   /*** Initializes a Thread with the current AccessControlContext.* @see #init(ThreadGroup,Runnable,String,long,AccessControlContext,boolean)*/private void init(ThreadGroup g, Runnable target, String name,long stackSize) {init(g, target, name, stackSize, null, true);}

调用init实际实现private，并给成员变量赋值

private void init(ThreadGroup g, Runnable target, String name,long stackSize, AccessControlContext acc,boolean inheritThreadLocals) {if (name == null) {throw new NullPointerException("name cannot be null");}this.name = name;Thread parent = currentThread();SecurityManager security = System.getSecurityManager();if (g == null) {/* Determine if it's an applet or not *//* If there is a security manager, ask the security managerwhat to do. */if (security != null) {g = security.getThreadGroup();}/* If the security doesn't have a strong opinion of the matteruse the parent thread group. */if (g == null) {g = parent.getThreadGroup();}}/* checkAccess regardless of whether or not threadgroup isexplicitly passed in. */g.checkAccess();/** Do we have the required permissions?*/if (security != null) {if (isCCLOverridden(getClass())) {security.checkPermission(SUBCLASS_IMPLEMENTATION_PERMISSION);}}g.addUnstarted();this.group = g;this.daemon = parent.isDaemon();this.priority = parent.getPriority();if (security == null || isCCLOverridden(parent.getClass()))this.contextClassLoader = parent.getContextClassLoader();elsethis.contextClassLoader = parent.contextClassLoader;this.inheritedAccessControlContext =acc != null ? acc : AccessController.getContext();this.target = target;setPriority(priority);if (inheritThreadLocals && parent.inheritableThreadLocals != null)this.inheritableThreadLocals =ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);/* Stash the specified stack size in case the VM cares */this.stackSize = stackSize;/* Set thread ID */tid = nextThreadID();}

3. 解析thread1.start();

成员变量group增加当前实例，并调用本地方法使用虚拟机启动线程

 public synchronized void start() {/*** This method is not invoked for the main method thread or "system"* group threads created/set up by the VM. Any new functionality added* to this method in the future may have to also be added to the VM.** A zero status value corresponds to state "NEW".*/if (threadStatus != 0)throw new IllegalThreadStateException();/* Notify the group that this thread is about to be started* so that it can be added to the group's list of threads* and the group's unstarted count can be decremented. *///group是成员变量 能加入线程对象数组内 group.add(this);boolean started = false;try {start0();started = true;} finally {try {if (!started) {group.threadStartFailed(this);}} catch (Throwable ignore) {/* do nothing. If start0 threw a Throwable thenit will be passed up the call stack */}}}

启动

    private native void start0();

private native void start0(); 是 Java 中的一个本地方法声明。

本地方法是一种在 Java 代码中声明但实际实现却在本地语言（如C或C++）中的方法。这通常用于与操作系统、硬件或其他底层资源进行交互的情况，因为本地语言可以更高效地访问底层资源。

在这个特定的声明中，start0() 方法是一个私有（private）本地方法，没有方法体。通过 native 关键字表示该方法的实现是在本地语言中完成的。

start0() 方法通常是与 Thread.start() 方法相关联的，用于启动线程的执行。在 Thread 类的实现中，start0() 方法的实际实现通常由底层虚拟机（JVM）提供，而不是在 Java 代码中定义。

因为 start0() 是一个本地方法，所以它的具体实现是由底层虚拟机提供的，并且无法在 Java 代码中直接查看或修改其实现。

4. this.target = target;

target 是定义的成员变量，类型为接口
private Runnable target;
this.target = target;作用是将实现此接口的类指向此接口，调用时会调用此接口的实现类

5.学习到什么

1.线程类通过公开方法或者构造方法为对象内部私有变量赋值，保护对象内部成员变量的安全。
2.线程启动会调用之前为成员变量赋值的变量使用