java 线程安全 锁

两个线程A，B。调用同一加锁代码块C，假如A先调用C，在A线程调用C完成之前，B线程要调用此代码块必须先等待，等A调用完成，B立马执行C.

package test;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;
import java.net.URLEncoder;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;

import net.sf.json.JSONObject;

import com.hlzt.wx.util.http.WxHttpClientUtils;
import com.hlzt.wx.util.msg_handler.MsgDispatcher;

public class ss {

	 public static void main(String[] args) throws UnsupportedEncodingException {
		 ddd d=new ddd("aaaaaaaaaaaaaa");
		 d.start();
		 ddd d2=new ddd("bbbbbbbbbbbbbb");
		 d2.start();

	}

	 public synchronized static void aa(String str)
		{
			System.out.println("1#########"+str);
			try {
				Thread.sleep(2000);
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}

			System.out.println("2#########"+str);

		}

}

class ddd  extends Thread{
	private String aaa;

	public ddd(String aaa) {
		this.aaa = aaa;
	}

	@Override
	public void run() {
		ss.aa(aaa);
	}

}