Synchronized and static synchronized in java interview

• During the interview, I encountered a question about synchronize and static synchronization, such as the title

In fact, my understanding is completely deviated, so after I came back, I studied it carefully and wrote a simpleDemo for your reference.

Summary: Adding synchronized to the front of the method is similar to the synchronized{xxxxxxx} code block, both are synchronized(this){xxxx} (Does it feel terrible?)

To lock the object, remember that it locks the entire object. If static is synchronized, the class is locked, so the answer is clear at a glance.

If you pursue performance, it is recommended that you use synchronized with caution

 

Answer: 

can not

can not

can not

can not

can

 

The demo is as follows
 

package cn.com.flaginfo;

import java.util.Date;
import java.util.concurrent.TimeUnit;

public class A {

	private static boolean isTrue;
	private static Object sss = new Object();
	
	public static synchronized void staticWrite(boolean b) throws InterruptedException{
		System.out.println("staticWrite·" + new Date());
		TimeUnit.SECONDS.sleep(2);
		isTrue = b;	
	}
	
	public static synchronized boolean staticRead() throws InterruptedException{
		System.out.println("staticRead·"+ new Date());
		TimeUnit.SECONDS.sleep(2);
		return isTrue;
	}
	
	public synchronized void write(boolean b) throws InterruptedException{
		System.out.println("write·"+ new Date());
		TimeUnit.SECONDS.sleep(2);
		isTrue = b;
	}
	
	public  void write1(boolean b) throws InterruptedException{
		
		synchronized(sss){
		System.out.println("write·"+ new Date());
		TimeUnit.SECONDS.sleep(2);
		isTrue = b;
		}
	}
	
	public synchronized boolean read() throws InterruptedException{
		System.out.println("read·"+ new Date());
		TimeUnit.SECONDS.sleep(2);
		return isTrue;
	}
	
	public static void main(String[] args) throws Exception{
		final A a = new A();
		new Thread(new Runnable(){

			@Override
			public void run() {
				
				try {
					System.out.println("调用staticWrite(true)");
					a.write(true);
//					A.staticWrite(true);
				} catch (InterruptedException e) {
					e.printStackTrace ();
				}
			}
			
		}).start();
		TimeUnit.MILLISECONDS.sleep(200);
		new Thread(new Runnable(){

			@Override
			public void run() {
				
				try {
					System.out.println("调用staticRead()");
//					A.staticRead();
					a.read();
				} catch (InterruptedException e) {
					e.printStackTrace ();
				}
			}
			
		}).start();
	}
}