用多線程去處理 "123","456","789" 三個字符串，然後以"147","258","369"輸出

import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;

/**
 * 用多線程去處理 "123","456","789" 三個字符串，然後以"147","258","369"輸出
 *
 */
public class ThreadSample {
    public static void main(String[] args) throws InterruptedException, ExecutionException {
        String str1 = "123",str2 = "456",str3 = "789";
        ProcessThread thread3 = new ProcessThread(str3, null);
        ProcessThread thread2 = new ProcessThread(str2, thread3);
        ProcessThread thread1 = new ProcessThread(str1, thread2);
        for (int i = 0; i < str1.length(); i++) {
            thread1.setIndex(i);    
            FutureTask<String> future = new FutureTask<String>(thread1);
            new Thread(future).start();
            String outStr = future.get();
            System.out.println(outStr);
        }
    }
}

輸出:
147
258
369

import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;

public class ProcessThread implements Callable<String>{
    private String value;
    private ProcessThread next;
    private Integer index;
    
    public String call() throws Exception {
        if(this.next!=null){
            this.next.setIndex(this.index);
            //開啓下一個線程
            FutureTask<String> future = new FutureTask<String>(this.next);
            new  Thread(future).start();
            String nextString = future.get();
            return value.charAt(this.index)+nextString;
        }
        return String.valueOf(value.charAt(this.index));
    }
    public ProcessThread(String value, ProcessThread next) {
        this.value = value;
        this.next = next;
    }
    //set/get 省略
}