Java

Question

假设我有很多对象：

public class Main {
    public static DB d1 = new DB(1);
    public static DB d2 = new DB(2);
    public static DB d3 = new DB(3);
    public static DB d4 = new DB(4);

我想修改它们。

    public static void main(String[] args) {
        d1.modifyObject();
        d2.modifyObject();
        d3.modifyObject();
        d4.modifyObject();
    }
}

和我希望他们同时修改，因为这需要一些时间。看来我需要多线程。

这是我的 DB class:

import java.awt.EventQueue;
import java.util.Date;
import java.util.Random;

public class DB {
    private int id = 0;
    private long field = 0;

    public void DB(int id) {
        this.id = id;
    }

    // The contents of this method are not very important.
    private void modifyField() {
        // [some database interactions which take some seconds to execute]
        // for simplicity, emulated with sleep:
        long newValue = 0;
        try {
            newValue = (this.id + new Date().getTime()) % 42;
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        this.field = newValue;
    }

    public void modifyObject() {
        Runnable r = new Runnable(){ @Override public void run() {
            this.modifyField(); // THIS DOES NOT WORK OF COURSE, I can't access the objects content from a thread
        }};
        EventQueue.invokeLater(r);
    }
}

我想让Main.d1、Main.d2、Main.d3、Main.d4等的内容在不耽误主线程的情况下进行更改。我曾经通过在 DB 本身中访问 Main.d1 来做到这一点。这显然只有在我只有一个对象时才有效。现在，由于我必须处理多个对象，我无法再静态访问 Main 的对象。

我的问题很简单，但恐怕没有简单的答案：我必须将哪些选项 this.modifyField(); 放入其自己的线程中？

如何让对象在线程中修改自身？

Answer 1

我认为你完全错了this。

这里：

    Runnable r = new Runnable(){ @Override public void run() {
        this.modifyField(); // THIS DOES NOT WORK OF COURSE, I can't access the objects content from a thread
    }};

this指的是new Runnable。您可以这样访问封闭的 DB 对象：

    Runnable r = new Runnable(){ @Override public void run() {
        DB.this.modifyField();
    }};

此外，如果您使用的是 Java 8，则可以使用方法参考更简洁地编写整个代码：

Runnable r = this::modifyField;

Answer 2

使用 ExecutorServce：

public void foo() throws InterruptedException {
    final ExecutorService executorService = newFixedThreadPool(4); //find what works best for you, setting the number of threads as the number of tasks will not be the best solution in all cases

    final Future<?> runD1Modify = executorService.submit(getModifyObjectRunnable(d1));
    final Future<?> runD2Modify = executorService.submit(getModifyObjectRunnable(d2));
    final Future<?> runD3Modify = executorService.submit(getModifyObjectRunnable(d3));
    final Future<?> runD4Modify = executorService.submit(getModifyObjectRunnable(d4));

    // or in java8

    final Future<?> runD1Modify = executorService.submit(() -> d1.modifyField());
    final Future<?> runD1Modify = executorService.submit(() -> d2.modifyField());
    final Future<?> runD1Modify = executorService.submit(() -> d3.modifyField());
    final Future<?> runD1Modify = executorService.submit(() -> d4.modifyField());
}

private Runnable getModifyObjectRunnable(final DB db) {
    return new Runnable() {
        @Override
        public void run() {
            db.modifyField();
        }
    };
}

Java - 使对象在线程中修改自身

Java - Make an object modify itself in a thread

multithreading

object

如何让对象在线程中修改自身？