线程之synchronized 块

①同一个对象中的两个线程

package co.test.synchronize; import java.util.ArrayList; import java.util.List; public class CopyOfTest implements Runnable { private List<String> list = new ArrayList<String>(); private int count = 0; public CopyOfTest(int whichThread) { count = whichThread; } public static void main(String[] args) { // 同一个对象中的两个线程-----------------------↓ CopyOfTest test = new CopyOfTest(0); Thread thread1 = new Thread(test); thread1.start(); Thread thread2 = new Thread(test); thread2.start(); // 同一个对象中的两个线程-----------------------↑ } @Override public void run() { if (count == 0) { function3(); } else { function4(); } } private void function3() { count = 1; synchronized (list) { System.out.println("function33333 is start"); try { // 模拟耗时操作 Thread.sleep(3000); list.add("bb"); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("function33333 is end"); } } private void function4() { synchronized (list) { System.out.println("function44444 is start"); System.out.println("list :" + list.size()); System.out.println("function44444 is end"); } } }
执行结果：

function33333 is start function33333 is end function44444 is start list :1 function44444 is end
function4等function3执行完之后才被执行

②两个对象中的两个线程

package co.test.synchronize; import java.util.ArrayList; import java.util.List; public class CopyOfTest implements Runnable { private List<String> list = new ArrayList<String>(); private int count = 0; public CopyOfTest(int whichThread) { count = whichThread; } public static void main(String[] args) { // 两个对象中的两个线程-----------------------↓ CopyOfTest test1 = new CopyOfTest(0); CopyOfTest test2 = new CopyOfTest(1); Thread thread1 = new Thread(test1); thread1.start(); Thread thread2 = new Thread(test2); thread2.start(); // 两个对象中的两个线程-----------------------↑ } @Override public void run() { if (count == 0) { function3(); } else { function4(); } } private void function3() { count = 1; synchronized (list) { System.out.println("function33333 is start"); try { // 模拟耗时操作 Thread.sleep(3000); list.add("bb"); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("function33333 is end"); } } private void function4() { synchronized (list) { System.out.println("function44444 is start"); System.out.println("list :" + list.size()); System.out.println("function44444 is end"); } } }
执行结果：

function33333 is start function44444 is start list :0 function44444 is end function33333 is end
function3和function4都处于执行状态