使用concurrenthashmap

Question

我想知道在以下代码中迭代hashmap之后是否可以访问我得到的值（我知道它们存储在map中但是想在循环外使用它们）。密钥和相应的值在循环内迭代。并发hashmap可以帮助我获取值并在循环外使用它们。

谢谢。

     public static void main(String[] args) {
    Map<String, List<String>> maleMap = new LinkedHashMap<String,  List<String>>();
Map<String, List<String>> femaleMap = new LinkedHashMap<String, List<String>>();
    try {

Scanner scanner = new Scanner(new FileReader(.txt));

        while (scanner.hasNextLine()) {
            String nextLine = scanner.nextLine();
            String[] column = nextLine.split(":");
            if (column[0].equals("male") && (column.length == 4)) {
                maleMap.put(column[1],
                Arrays.asList(column[2], column[3]));
        } else if (column[0].equals("female") && (column.length == 4)) {
        femaleMap.put(column[1],
                    Arrays.asList(column[2], column[3]));
            }
        }
        Set<Entry<String, List<String>>> entries = maleMap.entrySet();
        Iterator<Entry<String, List<String>>> entryIter = entries
                .iterator();
        while (entryIter.hasNext()) {
            Map.Entry entry = (Map.Entry) entryIter.next();
            Object key = entry.getKey(); // Get the key from the entry.

            List<String> value = (List<String>) entry.getValue();
            Object value1 = " ";
            Object value2 = " ";
            int counter = 0;
            for (Object listItem : (List) value) {
                Writer writer = null;
                Object Name = key;
                Object Age = null;
                Object ID = null;
                if (counter == 0) {// first pass assign value to value1
                    value1 = listItem;
                    counter++;// increment for next pass
                } else if (counter == 1) {// second pass assign value to
                                            // value2
                    value2 = listItem;
                    counter++;// so we dont keep re-assigning listItem for
                                // further iterations
                }
            }
            System.out.println(key + ":" + value1 + "," + value2);
            scanner.close();
            Writer writer = null;
            Object Name = key;
            Object Age = value1;
            Object ID = value2;

            try {
                String filename = ".txt";
            FileWriter fw = new FileWriter(filename, true); 

 fw.write("# Table" +  Name + "\n" + "map:"+ Name + " a d2rq:ClassMap;" + "\n"
 + "    dataStorage map:database;" + "\n"+ "Pattern " +"\""+ Name + "/@@"+ Age +    
 "." + ID + "@@\";" + "\n"+ "   class :" + Name +";"+"\n"+ "     ."+"\n");// 
                fw.close();
            } catch (Exception e) {
                e.printStackTrace();
            }

        }

Answer 1

ConcurrentHashMap旨在确保线程安全 如果你没有使用多个线程，那就更糟糕了。

您应该使用MultiMap。

您可以始终访问循环外的值。

Answer 2

ConcorrentHashMap是故障安全的。它不会给出任何并发的修改异常。它适用于多线程操作。 ConcurrentHashMap的整个实现与HashMap相同，但是在检索元素的同时，HashMap锁定整个映射，限制了进行进一步的修改，从而导致并发修改异常。但是在ConcurrentHashMap中，锁定发生在存储桶级别，因此不存在提供并发修改异常的机会。