Use of atomicinteger

AtomicInteger Use

Why java.util.concurrent.atomic.AtomicInteger

++i,–i Not thread safe , Three steps involved ,1、 obtain i value 2、 Carry out operations 3、 Write back the new value . multithreading , The results exceeded expectations .

AtomicInteger What methods are provided

The code comments indicate the methods provided . While using , Familiar with .

import static org.junit.Assert.*;
import java.util.concurrent.atomic.AtomicInteger;

public class Test {
    
   public static void main(String args[]) throws InterruptedException {
    
       final AtomicInteger value = new AtomicInteger(10);
       // Get value 
       assertEquals(value.get(),10);
       // Set the value 
       value.set(5);
       assertEquals(value.get(),5);

       // Compare and set 
       //  Currently compared with expectations , Not equal, not updated .
       assertEquals(value.compareAndSet(3, 2), false);
       assertEquals(value.get(), 5);
       //  Currently compared with expectations , Equal update .
       assertEquals(value.compareAndSet(5, 2), true);
       assertEquals(value.get(), 2);

       //++i
       assertEquals(value.incrementAndGet(), 3);
       //+n
       assertEquals(value.getAndAdd(5),3);
       assertEquals(value.get(),8);
       //i++
       assertEquals(value.getAndIncrement(),8);
       assertEquals(value.get(),9);
       //+n
       assertEquals(value.addAndGet(2),11);

       //--i
       assertEquals(value.decrementAndGet(),10);
       //i--
       assertEquals(value.getAndDecrement(),10);
       assertEquals(value.get(),9);
       //i==n
       assertEquals(value.getAndSet(6),9);
       assertEquals(value.get(),6);
   }
}

verification AtomicInteger Thread safety

import java.util.concurrent.atomic.AtomicInteger;
import static org.junit.Assert.assertEquals;
class Test {
    
    static int ivalue = 10;
   public static void main(String args[]) throws InterruptedException {
    
       // Use  AtomicInteger, Thread safety 
       // ordinary  ++i, Thread unsafe 
       final AtomicInteger value = new AtomicInteger(10);
       final int threadSize = 50000;
       Thread[] t = new Thread[threadSize];
       for(int i=0;i<threadSize;i++){
    
            t[i] = new Thread(){
    
                @Override
                public void run(){
    
                    value.incrementAndGet();
                    ++ivalue;
                }
            };
       }
       for(Thread tt :t){
    
           tt.start();
       }
       for(Thread tt: t){
    
           tt.join();
       }
       assertEquals(value.get(),threadSize+10);//true
       assertEquals(ivalue,threadSize+10);// When there are enough threads ,false
   }
}