多線程-Thread，Runnable，Callable，Future，RunnableFuture，FutureTask

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類圖：

 

先看各自的源碼：

public interface Runnable {    public abstract void run();}

　　

publicclass Thread implements Runnable {    /* What will be run. */    private Runnable target;}

Thread與Runnable其實是一個裝飾器模式。

public interface Callable<V> {    V call() throws Exception;}

　　

public interface Future<V> {    boolean cancel(boolean mayInterruptIfRunning);    boolean isCancelled();    boolean isDone();    V get() throws InterruptedException, ExecutionException;    V get(long timeout, TimeUnit unit)        throws InterruptedException, ExecutionException, TimeoutException;}

　　

public interface RunnableFuture<V> extends Runnable, Future<V> {    void run();}

　　

public class FutureTask<V> implements RunnableFuture<V> { /** The underlying callable; nulled out after running */    private Callable<V> callable; /** The result to return or exception to throw from get() */    private Object outcome;    public void run() {        if (state != NEW ||            !UNSAFE.compareAndSwapObject(this, runnerOffset,                                         null, Thread.currentThread()))            return;        try {            Callable<V> c = callable;            if (c != null && state == NEW) {                V result;                boolean ran;                try {                    result = c.call();                    ran = true;                } catch (Throwable ex) {                    result = null;                    ran = false;                    setException(ex);                }                if (ran)                    set(result);            }        } finally {            // runner must be non-null until state is settled to            // prevent concurrent calls to run()            runner = null;            // state must be re-read after nulling runner to prevent            // leaked interrupts            int s = state;            if (s >= INTERRUPTING)                handlePossibleCancellationInterrupt(s);        }    }}

從類的結構來看： 
Runnable，Callable，Future介面本是互相獨立的，沒有直接的關係。 
而Thread的一系列建構函式需要的是Runnable對象，所以Callable對象並不適合Thread建構函式，而是藉助於FutureTask這個類，該類實現具有Future和Runnable介面能力的類，同時組合Callable對象，FutureTask在run()方法中調用Callable的call()方法，這是個典型的適配器模式： 
Runable是個目標介面，定義了Thread所需的介面； 
Callable是被適配介面，定義了一個已經存在的介面方法call() 
FutureTask是個適配器類，作為一個轉換器，將Runnable和Callable適配，適配器類是適配器模式的核心，它通過實現RunnableFuture和組合Callable使得兩者產生關係。

多線程-Thread，Runnable，Callable，Future，RunnableFuture，FutureTask