我們先來看段示例代碼
import java.util.concurrent.Callable;import java.util.concurrent.FutureTask;public class Main { public static void main(String[] args) { //方法一：繼承Thread int i = 0;// for(; i < 100; i++){// System.out.println(Thread.currentThread().getName() + " " + i);// if (i == 5) {// ThreadExtendsThread threadExtendsThread = new ThreadExtendsThread();// threadExtendsThread.start();// }// } //方法二：實現Runnable// for(i = 0; i < 100; i++){// System.out.println(Thread.currentThread().getName() + " " + i);// if (i == 5) {// Runnable runnable = new ThreadImplementsRunnable();// new Thread(runnable).start();// new Thread(runnable).start();// }// } //方法三：實現Callable接口 Callable<Integer> callable = new ThreadImplementsCallable(); FutureTask<Integer> futureTask = new FutureTask<>(callable); for(i = 0; i < 100; i++){ System.out.println(Thread.currentThread().getName() + " " + i); if (i == 5) { new Thread(futureTask).start(); new Thread(futureTask).start(); } } try { System.out.println("futureTask ruturn: " + futureTask.get()); } catch (Exception e) { e.printStackTrace(); } }}接下來我們來詳細探討下Java 實現多線程的幾種方式
方法一，繼承自Thread
public class ThreadExtendsThread extends Thread { private int i; @Override public void run() { for(; i < 100; i++) { System.out.println(getName() + " " + i); } }}run方法為線程執行體，ThreadExtendsThread對象即為線程對象。
方法二，實現Runnable接口
public class ThreadImplementsRunnable implements Runnable { private int i; @Override public void run() { for(; i < 100; i++){ System.out.println(Thread.currentThread().getName() + " " + i); } }}run方法為線程執行體，使用時New一個Thread對象，Runnable對象作為target傳遞給Thread對象。且同一個Runnable對象可作為多個Thread的target，這些線程均共享Runnable對象的實例變量。
方法三，實現Callable接口
import java.util.concurrent.Callable;public class ThreadImplementsCallable implements Callable<Integer> { private int i; @Override public Integer call() throws Exception { for(; i < 100; i++){ System.out.println(Thread.currentThread().getName() + " " + i); } return i; }}Callable接口類似于Runnable接口，但比對方強大，線程執行體為call方法，該方法具有返回值和可拋出異常。使用時將Callable對象包裝為FutureTask對象，通過泛型指定返回值類型。可稍候調用FutureTask的get方法取回執行結果。
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