atomic包下幾個(gè)類的用法

1.原子更新引用類型

以原子的方式更新某個(gè)引用對(duì)象,可以使用如下的類去實(shí)現(xiàn)
AtomicReference
使用過(guò)程中,更新的時(shí)候要避免錯(cuò)誤使用

/**
 * 原子更新整個(gè)引用類型
 * @author senninha
 *
 */
public class AtomicReferenceTest {
    public AtomicReference<User>  user = new AtomicReference<User>(null);
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        AtomicReferenceTest t = new AtomicReferenceTest();
        t.user.set(new User("senninha","21"));
        User user = t.user.get();
        //錯(cuò)誤的更新方法
        user.setAge("10");
        //正確的更新方法
        user = new User("senninha","22");
        t.user.set(user);
    }

}

class User{
    private String username;
    public User(String username, String age) {
        super();
        this.username = username;
        this.age = age;
    }
    public String getUsername() {
        return username;
    }
    public String getAge() {
        return age;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public void setAge(String age) {
        this.age = age;
    }
    private String age;
    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("User [username=");
        builder.append(username);
        builder.append(", age=");
        builder.append(age);
        builder.append("]");
        return builder.toString();
    }
    
}

2.帶時(shí)間戳的原子更新

避免更新時(shí)候出現(xiàn)ABA這樣的錯(cuò)誤,使用帶時(shí)間戳的原子更新方式

/**
*
*
**/
public class AtomicStampReferenceTest {
    public AtomicStampedReference<User> user = null;
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        User u = new User("senninha","21");
        AtomicStampReferenceTest aft = new AtomicStampReferenceTest();
        //這里可以用時(shí)間戳來(lái)表示0
        aft.user = new AtomicStampedReference<User>(u, 0);
        u = new User("senninha","22");
        //aft.user.set(u,System.currentTimeMillis());
        aft.user.set(u, aft.user.getStamp() + 1);
        System.out.println(aft.user.getStamp() + " " + aft.user.getReference());
    }

}

3.原子更新類中某個(gè)字段

如1那里,其實(shí)要更新的只是age字段,就可以使用原子更新某個(gè)字段的方法
AtomicIntegerFieldUpdater
AtomicLongFieldUpdater
AtomicReferenceFieldUpdater
需要把他們聲明為public volatile類型

    /**
     * 只更新類中的某個(gè)字段的時(shí)候
     * 只需要把要更新的那個(gè)字段設(shè)置為public volatile,利用反射來(lái)實(shí)現(xiàn)CAS操作
     */
    public static void atomicReferenceFieldUpdater(){
    //User類中的age字段需要進(jìn)行原子操作,類型是String,字段名是age
        AtomicReferenceFieldUpdater arfu = AtomicReferenceFieldUpdater.newUpdater(User.class, String.class, "age");
        User u = new User("senninha","12");
        arfu.compareAndSet(u, u.age, "13");
        System.out.println(u.getAge());
    }
}

class User{
    public String username;
    public volatile String age;
    
    public User(String username, String age) {
        super();
        this.username = username;
        this.age = age;
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder();
        builder.append("User [username=");
        builder.append(username);
        builder.append(", age=");
        builder.append(age);
        builder.append("]");
        return builder.toString();
    }
    
}

4.原子更新數(shù)組

傳入后的會(huì)重新復(fù)制一份數(shù)組的拷貝,所以可以用原數(shù)組的值作為compare的比較對(duì)象.

    /**
     * 原子更新數(shù)組
     */
    public static void atomicArrayUpdater(){
        User[] user = new User[2];
        user[0] = new User("senninha", "1");
        user[1] = new User("senninha", "2");
        AtomicReferenceArray<User> ara = new AtomicReferenceArray<User>(user);
        //index,更新前的expect對(duì)象,如果expect傳入新的對(duì)象
        ara.weakCompareAndSet(0, user[0], new User("senninha","3"));
        System.out.println(user[0]);
        System.out.println(ara.get(0));
    }