HashMapTraversal.java

import java.util.*;

public class Main {
    public static void main(String args[])
    {
        Map<Integer, Integer> map = new HashMap();
        map.put(1, 3);
        map.put(2, 4);
        map.put(5, 7);

        /* Method 1, to use entrySet() */
        /*
        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
            System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
        }
        */

        /* Method 2, to use keySet() and valueSet() */
        /* Method 3, iterator */
        Iterator it = map.entrySet().iterator();  // Set has iterator, but HashMap doesn't
        while (it.hasNext()) {
            Map.Entry<Integer, Integer> entry = (Map.Entry)it.next();  // Iterator要强制转换
            System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());
        }
    }
}