关于java：为什么StringBuilder访问似乎是同步的？

Why does StringBuilder access appear to be synchronized?

本问题已经有最佳答案，请猛点这里访问。

我想知道StringBuilder和StringBuffer类与实际使用之间的区别。因此，我编写了两个代码片段，其中我同时生成了3个线程，这些线程使用了StringBuilder和StringBuffer对象。

当我运行代码时，我希望所有3个线程在StringBuilder的情况下同时运行，在StringBuffer的情况下以同步方式运行。但在这两种情况下，它们都以同步方式运行。那么，StringBuffer类的用途是什么呢？困惑：

(对于字符串对象，所有3个线程同时运行)。我将分享代码片段供您参考。如果我理解多线程本身的概念是错误的，请纠正我。请同时更正代码。

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// StringBuilder...

public class MultiTread implements Runnable{
private StringBuilder name;
public MultiTread(StringBuilder string){
name=string;
}

public void run(){
for(int i=0; i<=10; i++){
System.out.println(name.append(i));
}
}
public static void main(String[] args){
Thread th = new Thread(new MultiTread(new StringBuilder("thread1:")));
Thread th1 = new Thread(new MultiTread(new StringBuilder("thread2:")));
Thread th2 = new Thread(new MultiTread(new StringBuilder("thread3:")));

th.start();
th1.start();
th2.start();
}
}

..................

//StringBuffer...

public class MultiTreadBuf implements Runnable{
private StringBuffer name;
public MultiTreadBuf(StringBuffer string){
name=string;
}

public void run(){
for(int i=0; i<=10; i++){
System.out.println(name.append(i));
}
}
public static void main(String[] args){
Thread th = new Thread(new MultiTreadBuf(new StringBuffer("thread1:")));
Thread th1 = new Thread(new MultiTreadBuf(new StringBuffer("thread2:")));
Thread th2 = new Thread(new MultiTreadBuf(new StringBuffer("thread3:")));

th.start();
th1.start();
th2.start();
}
}

........

//String....

public class MuiltiTreadStr implements Runnable{
private String name;
public MuiltiTreadStr(String string){
name=string;
}

public void run(){
for(int i=0; i<=10; i++){
System.out.println(name+i);
}
}
public static void main(String[] args){
System.out.println("main begins...");
Thread th = new Thread(new MuiltiTreadStr("thread1:"));
Thread th1 = new Thread(new MuiltiTreadStr("thread2:"));
Thread th2 = new Thread(new MuiltiTreadStr("thread3:"));
System.out.println("spawning 3 threads...");
th.start();
th1.start();
th2.start();
System.out.println("main ends...");
}
}