英文:
How can I make my hashmap public to be printed from anywhere in java?
问题
我想能够在一个线程方法内打印一个哈希映射（hashmap），但是我无法弄清楚如何使其成为全局变量，或者如何将哈希映射作为参数传递给函数。有人能帮我解决这个问题吗？
我认为我的问题可能是，也许我是从一个文件中处理所有事情？像这样从一个文件中实现我需要的功能是可能的吗？
谢谢。
import java.util.Scanner;
import java.util.HashMap;
import java.net.*;
import java.io.*;
import java.lang.Thread;
public class Server{
public static void main(String[] args){
if (args.length < 1) return;
HashMap<String, String> Distances = new HashMap<String, String>(); // 这里是映射
menu mThread = new menu(Distances); // 将映射传递给menu线程
try{
InetAddress ip = InetAddress.getLocalHost();
Distances.put(ip.toString(), "0");
System.out.println(Distances);
} catch (UnknownHostException e){
e.printStackTrace();
}
int port = Integer.parseInt(args[0]);
try (ServerSocket serverSocket = new ServerSocket(port)) {
System.out.println("server is listening on port " + port);
while(true){
Socket socket = serverSocket.accept();
System.out.println("Client connected");
serverSocket.close();
System.exit(0);
}
} catch(IOException ex) {
System.out.println("exception");
ex.printStackTrace();
}
}
}
class menu implements Runnable{
HashMap<String, String> Distances; // 存储传递的映射
menu(HashMap<String, String> distances){
Distances = distances; // 初始化映射
Thread m = new Thread(this);
m.start(); // 使用start方法来启动线程
}
public void run(){
printMenu();
}
public void printMenu(){
Scanner input = new Scanner(System.in);
int choice = 0; // 初始化choice
System.out.println("1. help\n 2. routing\n 3. myPort");
while(choice != 4){
choice = input.nextInt();
if (choice == 1)
System.out.println("control c to quit, otherwise make another selection");
else if (choice == 2)
System.out.println(Distances); // 这里是问题所在
}
}
}
英文:
I want to be able to print a hashmap inside a threaded method, but I can't figure out how to make it global or how to pass the hashmap as a parameter to the function. Could someone help me with this please?
I think my problem is that, maybe, I am doing everything from one file? Is it possible to do what I need from one file like this?
Thank you.
import java.util.Scanner;
import java.util.HashMap;
import java.net.*;
import java.io.*;
import java.lang.Thread;
public class Server{
public static void main(String[] args){
if (args.length < 1) return;
HashMap<String, String> Distances = new HashMap<String, String>(); // here's the map
menu mThread = new menu();
try{
InetAddress ip = InetAddress.getLocalHost();
Distances.put(ip.toString(), "0");
System.out.println(Distances);
} catch (UnknownHostException e){
e.printStackTrace();
}
int port = Integer.parseInt(args[0]);
try (ServerSocket serverSocket = new ServerSocket(port)) {
System.out.println("server is listening on port " + port);
while(true){
Socket socket = serverSocket.accept();
System.out.println("Client connected");
serverSocket.close();
System.exit(0);
}
} catch(IOException ex) {
System.out.println("exception");
ex.printStackTrace();
}
}
}
class menu implements Runnable{
menu(){
Thread m = new Thread(this);
m.run();
}
public void run(){
printMenu();
}
public void printMenu(){
Scanner input = new Scanner(System.in);
int choice;
System.out.println("1. help\n 2. routing\n 3. myPort");
while(choice != 4){
choice = input.nextInt();
if (choice == 1)
System.out.println("control c to quit, otherwise make another selection");
else if (choice == 2)
System.out.println(Distances); // here is the issue
}
}
}
答案1
得分: 1
首先，您应该知道 HashMap 不是线程安全的，因此最好使用 ConcurrentHashMap。实现所需行为的一种方法是创建一个类，该类将接受一个地图作为构造函数参数，这样您就可以在运行方法中传递并使用它。然后，您需要将该类的实例传递给线程。这里有一个非常简单的示例 - https://intellipaat.com/community/24428/how-can-i-pass-a-parameter-to-a-java-thread。
英文:
Firstly, you should know that HashMap isn't thread safe, so it would be better to use ConcurentHashMap. One of the way to implement desired behaviour is to create a class that would accept a map as constructor parameter, so you will be able to pass it and use it a run method. Then you have to pass instance of the class to the Thread. Here's a really simple example - https://intellipaat.com/community/24428/how-can-i-pass-a-parameter-to-a-java-thread.
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