Java,我如何在main之外创建一个哈希映射,但在main或其他方法中引用它

Question

Java,我如何在main之外创建一个哈希映射但在main或其他方法中引用它引入java.util.*;

import java.util.Map.Entry;

// Create a hash map 

        HashMap<String, Double> hm = new HashMap<String, Double>();

// Put elements into the map

        hm.put("John Doe", new Double(3434.34)); 
        hm.put("Tom Smith", new Double(123.22)); 
        hm.put("Jane Baker", new Double(1378.00)); 
        hm.put("Todd Hall", new Double(99.22)); 
        hm.put("Ralph Smith", new Double(-19.08));

class HashMapDemo 
{ 

    public static void main(String args[])
    { 
        // Get a set of the entries

        Set<Entry< String, Double> > set = hm.entrySet();

        // Get an iterator

        Iterator<Entry< String, Double> > i = set.iterator();

        // Display elements

        while(i.hasNext())
        { 
            Entry< String, Double > me = i.next(); 
            System.out.print( me.getKey() + ": " ); 
            System.out.println( me.getValue() ); 
        }

        System.out.println();

        // Deposit 1000 into John Doe's account

        double balance = hm.get( "John Doe" ).doubleValue(); 
        hm.put( "John Doe", new Double(balance + 1000) ); 
        System.out.println( "John Doe's new balance: " + hm.get("John Doe"));

    } 
}

Answer 1

问题是您正在尝试从静态main访问实例值.要解决这个问题,只需将HashMap设置为静态即可.

static HashMap<String, Double> hm = new HashMap<String, Double>();

static {
    hm.put("John Doe", new Double(3434.34)); 
    hm.put("Tom Smith", new Double(123.22)); 
    hm.put("Jane Baker", new Double(1378.00)); 
    hm.put("Todd Hall", new Double(99.22)); 
    hm.put("Ralph Smith", new Double(-19.08));
}

现在这条线路可以访问 hm

Set<Entry< String, Double> > set = hm.entrySet();