if else语句出现错误。变量变为隐藏[重复]

Question

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• What does a “Cannot find symbol” or “Cannot resolve symbol” error mean?13个答案

这是我的用于将消息发送到队列的代码。但是当我使用if else语句时，我的某些变量（代理，队列，用户等）被隐藏了。当我运行程序时，抛出此错误-Error：（71，13）java：找不到符号symbol：变量计数位置：class Producer

import org.apache.activemq.jms.pool.PooledConnectionFactory;
import org.apache.activemq.ActiveMQConnectionFactory;
import java.util.Scanner;
import javax.jms.*;

public class Producer {

    public static void main(String[] args) throws JMSException {

        Scanner scanner = new Scanner(System.in);
        System.out.println("Use existing parameters/ YES or NO");
        String existing = scanner.nextLine();
        if (existing.equals ("NO")) {

            System.out.println("Give me your broker ULR");
            String broker = scanner.nextLine();
            System.out.println("Give me your broker User Name");
            String user = scanner.nextLine();

        }else{
            String broker = "failover:(ssl://b-5dfe451d-09e7-46aa-8be0-814bb4b26227-1.mq.eu-central-1.amazonaws.com:61617," +
                    "ssl://b-5dfe451d-09e7-46aa-8be0-814bb4b26227-2.mq.eu-central-1.amazonaws.com:61617)";
            String user = "koco";
            String pass = "qwertyui1234";
            String queue = "queue1";
            String message = "Kak si ti dobre li si kaji";
            int count = 1;
        }

        ActiveMQConnectionFactory connFactory = new ActiveMQConnectionFactory(broker);

        // Specify the master username and password.
        connFactory.setUserName(user);
        connFactory.setPassword(pass);

        //PooledConnectionFactory pooledConnFactory = new PooledConnectionFactory();
        //pooledConnFactory.setConnectionFactory(connFactory);
        //pooledConnFactory.setMaxConnections(10);

        //Connection producerConnection = pooledConnFactory.createConnection();
        Connection producerConnection = connFactory.createConnection();
        producerConnection.start();

        Session producerSession =
                producerConnection.createSession(false, Session.AUTO_ACKNOWLEDGE);

        Destination producerDest = producerSession.createQueue(queue);

        MessageProducer producer = producerSession.createProducer(producerDest);
        producer.setDeliveryMode(DeliveryMode.NON_PERSISTENT);

        TextMessage producerMessage = producerSession.createTextMessage(message);

        for (int i = 0; i < count; i++) {
        producer.send(producerMessage);
        }

        if (count == 1){
            System.out.println("Message sent successfully");
        }else {
            System.out.println("Messages sent successfully");
        }
        producer.close();
        producerSession.close();
        producerConnection.close();
    }
}

Answer 1

您在{}块内声明了变量，所以一旦离开该块，变量就消失了。

在{}块之前声明变量，并且在块关闭之后它们仍然存在。

Answer 2

您需要在else语句之外定义变量计数，否则，您将无法访问它。

        Scanner scanner = new Scanner(System.in);
        System.out.println("Use existing parameters/ YES or NO");
        String existing = scanner.nextLine();
        int count = -1;
        if (existing.equals ("NO")) {

            System.out.println("Give me your broker ULR");
            String broker = scanner.nextLine();
            System.out.println("Give me your broker User Name");
            String user = scanner.nextLine();

        }else{
            String broker = "failover:(ssl://b-5dfe451d-09e7-46aa-8be0-814bb4b26227-1.mq.eu-central-1.amazonaws.com:61617," +
                    "ssl://b-5dfe451d-09e7-46aa-8be0-814bb4b26227-2.mq.eu-central-1.amazonaws.com:61617)";
            String user = "koco";
            String pass = "qwertyui1234";
            String queue = "queue1";
            String message = "Kak si ti dobre li si kaji";
            count = 1;
        }

Answer 3

变量user，broker，pass，queue，count等在if else块中声明，并且是局部变量，在这些块之外不可见，您需要在类级别/全局或在方法级别至少声明这些变量在这里是Main的情况下，以便它们可以被该方法中的其他块访问。您可以在声明了String Existing之后立即声明这些变量，但我建议不要像现在在else块中那样重新声明它们，否则这些变量将被视为特定于该特定块的局部变量，因此不会在外面可用。