困惑（線程鎖）

寫兩種常用的單例模式實現，對比一下兩種方式的實現有什麼差異：

No1：

public class Test {
	
	private static Test instance = null;
	
	public static Test getInstance()
	{
		synchronized (Test.class) {
	        	if (instance == null) {
		        	instance = new Test();
		   	}
		}
		return instance;
	}
}

No2：

public class Test {
	
	private static Test instance = null;
	
	public synchronized static Test getInstance()
	{
		if (instance == null) {
			instance = new Test();
		}
		return instance;
	}
}