Java 之 AtomicReference

写在前面：

AtomicReference类提供了一个可以原子读写的对象引用变量。 原子意味着尝试更改相同AtomicReference的多个线程（例如，使用比较和交换操作）不会使AtomicReference最终达到不一致的状态。 AtomicReference甚至有一个先进的compareAndSet（object expect. object update）方法，它可以将引用与预期值（引用）进行比较，如果它们相等，则在AtomicReference对象内设置一个新的引用。

创建一个AtomicReference:

AtomicReference atomicReference = new AtomicReference();

String initialReference = "the initially referenced string";
AtomicReference atomicReference = new AtomicReference(initialReference);

 创建一个类型的AtomicReference:

AtomicReference<String> atomicStringReference = new AtomicReference<String>();

获取值:

AtomicReference atomicReference = new AtomicReference("first value referenced");

String reference = (String) atomicReference.get();

赋值:

AtomicReference atomicReference = 
     new AtomicReference();
    
atomicReference.set("New object referenced");

比较赋值:

        String initialReference = "initial value referenced";

        AtomicReference<String> atomicStringReference =
                new AtomicReference<String>(initialReference);

        System.out.println(atomicStringReference.get());  //initial value referenced

        String newReference = "new value referenced";
        // 预期值（第一个）与已存在内存值比较，如果相等则更新为第二个
        boolean exchanged = atomicStringReference.compareAndSet(initialReference, newReference);
        System.out.println("exchanged: " + exchanged);   //true,
        System.out.println(atomicStringReference.get());  //new value referenced


        exchanged = atomicStringReference.compareAndSet(initialReference, newReference);
        System.out.println("exchanged: " + exchanged);  //false
        System.out.println(atomicStringReference.get());  //new value referenced