Callable与Future

Callable与Runnable类似，但是有返回值，其接口是一个参数化的类型，只有一个call方法（类似Runnable中的run方法）
Future保存异步计算的结果，可以启动一个计算（callable），将Future对象交付给线程即可。当计算结束时，通过get方法获取计算结果。若计算未完成，则调用被阻塞，直到完成。可以通过isDone方法判断计算是否完成。
FutureTask包装器，可将Callable转换为Future和Runnable，同时实现二者的接口。

Callable_1 callable1=new Callable_1();FutureTask<Integer> result=new FutureTask<>(callable1);new Thread(result).start();result.get();

eg1:通过callable和future打印一组数据

package com.lmr.thread;import java.util.concurrent.ExecutionException;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors;import java.util.concurrent.Future;import java.util.concurrent.FutureTask;public class Callable_Future_1 {    public static void main(String[] args) {        Callable_1 callable1=new Callable_1();        FutureTask<Integer> result=new FutureTask<>(callable1);        new Thread(result).start();//启动result的FutureTask对象,去执行callable1的call方法        System.out.println("main thread is running");        try {            System.out.println("result: "+result.get());//获取结果        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (ExecutionException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        System.out.println("main thread is ending");    }}public class Callable_1 implements Callable<Integer>{    @Override    public Integer call() throws Exception {        // TODO Auto-generated method stub        System.out.println("callable is runing");        int sum=0;        for(int i=0;i<10;i++){            Thread.sleep(1000);            sum+=i;            System.out.println(i+" - "+sum);//每隔1秒打印数据        }        return sum;    }}

通过打印的结果，我们发现到程序跑到get方法时，并没有获取到结果，而是等callable1的call方法执行完毕后，才会打印结果

callable is runingmain thread is running0 - 01 - 12 - 33 - 64 - 105 - 156 - 217 - 288 - 369 - 45result: 45main thread is ending

eg2：搜索指定目录下所有文件内容，计算关键字的个数

package com.lmr.thread;import java.io.File;import java.io.FileNotFoundException;import java.util.ArrayList;import java.util.List;import java.util.Scanner;import java.util.concurrent.Callable;import java.util.concurrent.ExecutionException;import java.util.concurrent.Future;import java.util.concurrent.FutureTask;public class Callable_Future_2 {    public static void main(String[] args) {        String directory="E:\\Java_Swing\\src\\com\\swing";        String keyword="JPanel";        MatchCount counter=new MatchCount(new File(directory), keyword);        FutureTask<Integer> task=new FutureTask<>(counter);        Thread t=new Thread(task);        t.start();        try {            System.out.println("-------------  "+task.get());        } catch (InterruptedException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } catch (ExecutionException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }}class MatchCount implements Callable<Integer>{    private File directory;    private String keyword;    private int count;//关键字数目    public MatchCount(File directory,String keyword) {        // TODO Auto-generated constructor stub        this.directory=directory;        this.keyword=keyword;    }    @Override    public Integer call() throws Exception {        // TODO Auto-generated method stub        count=0;        try{            File[] files=directory.listFiles();            List<Future<Integer>> results=new ArrayList<>();//Future对象List            for(File file:files){                if(file.isDirectory()){                    MatchCount counter=new MatchCount(file, keyword);//递归遍历                    FutureTask<Integer> task=new FutureTask<>(counter);                    results.add(task);                    Thread t=new Thread(task);                    t.start();                }                else{                    if(search(file)){//若是文件，则去计算数目                        count+=searchsum(file);                    }                }            }            for(Future<Integer> result:results){//当该目录下所有文件的Future计算完后，累加数目                count+=result.get();            }        }        catch (Exception e) {            // TODO: handle exception        }        return count;    }    public boolean search(File file){//判断文件是否有关键字        try{            Scanner in=new Scanner(file);            boolean found=false;            while(!found&&in.hasNextLine()){                String line=in.nextLine();                if(line.contains(keyword)){                    found=true;                }            }            return found;        }        catch (Exception e) {            // TODO: handle exception            return false;        }    }    public int searchsum(File file) throws FileNotFoundException {//关键字计数        Scanner in = new Scanner(file);        int found = 0;        while (in.hasNextLine()) {            String line = in.nextLine();            while (line.contains(keyword)) {                System.out.println(line);                line=line.substring(line.indexOf(keyword)+keyword.length());                found++;            }        }        return found;    }}