我添加了另一个答案，因为我还没有添加评论给其他人的帖子。

>事实上，同步是用于代码，而不是对象或数据。在同步块中用作参数的对象引用表示锁定。

所以如果你有如下代码：

class Player {

// Same instance shared for all players... Don't show how we get it now.

// Use one dimensional board to simplify, doesn't matter here.

private List[] fields = Board.getBoard();

// Current position

private int x;

public synchronized int getX() {

return x;

}

public void setX(int x) {

synchronized(this) { // Same as synchronized method

fields[x].remove(this);

this.x = x;

field[y].add(this);

}

}

}

然后尽管在同步块上存在，但对字段的访问不受保护，因为锁不一样(它在不同的实例上)。因此，您的主板的播放器列表可能会变得不一致，并导致运行时异常。

相反，如果你写下面的代码，它将工作，因为我们只有一个共享锁为所有玩家：

class Player {

// Same instance shared for all players... Don't show how we get it now.

// Use one dimensional board to simplify, doesn't matter here.

private List[] fields;

// Current position

private int x;

private static Object sharedLock = new Object(); // Any object's instance can be used as a lock.

public int getX() {

synchronized(sharedLock) {

return x;

}

}

public void setX(int x) {

synchronized(sharedLock) {

// Because of using a single shared lock,

// several players can't access fields at the same time

// and so can't create inconsistencies on fields.

fields[x].remove(this);

this.x = x;

field[y].add(this);

}

}

}

=>确保只使用一个锁来访问所有玩家，否则您的棋盘状态将不一致。