One Java question every day [11] and one java question 11

One Java question every day [11] and one java question 11

Question

How does synchronized implement thread synchronization? Modify the MyRunnableThread class in every Java question [10] to solve the problem where all three threads get 10.

Answer

Method 1:

Use the synchronized keyword to wrap code blocks that require thread security to achieve thread synchronization. Syntax format:

Synchronized (expression) {// code to be Synchronized}

The MyRunnableThread class in a Java question [10] Every day is changed:

package me.huangzijian;public class MyRunnableThread implements Runnable {    private int num = 10;    private Object obj = new Object();    @Override    public void run() {        int count = num;        for (int i = 0; i < count; i++) {            synchronized (obj) {                System.out.println(Thread.currentThread().getName() + ":" + num);                num--;            }        }    }}

 

Method 2:

The synchronized keyword is used to modify the method, and the whole method is used for process thread synchronization. Syntax format:

Public synchronized void function () {// method code}

The MyRunnableThread class in a Java question [10] Every day is changed:

package me.huangzijian;public class MyRunnableThread implements Runnable {    private int num = 10;    private Object obj = new Object();    @Override    public synchronized void run() {        int count = num;        for (int i = 0; i < count; i++) {            System.out.println(Thread.currentThread().getName() + ":" + num);            num--;        }    }}

Divergent thinking

1. synchronized keyword modifier. If no expression exists, how does it obtain the synchronization lock?

Answer:

2. For method 1, if all objects passed to synchronized are new, can the synchronization effect be achieved?

A: No. Because different threads correspond to different synchronization locks and are not exclusive, thread synchronization will become invalid.