Four ways to traverse a Map

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public static void main(String[] args) {
 Map map = new HashMap();
 map.put("1", "value1");
 map.put("2", "value2");
 map.put("3", "value3");

 //The first type: commonly used, secondary value
 System.out.println("traverse key and value through Map.keySet: ");
 for (String key : map.keySet()) {
 System.out.println("key= "+ key + " and value= " + map.get(key));
 }

 //The second
 System.out.println("Use iterator to traverse key and value through Map.entrySet:");
 Iterator> it = map.entrySet().iterator();
 while (it.hasNext()) {
 Map.Entry entry = it.next();
 System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
 }

 //The third type: recommended, especially when the capacity is large
 System.out.println("traverse key and value through Map.entrySet");
 for (Map.Entry entry : map.entrySet()) {
 System.out.println("key= " + entry.getKey() + " and value= " + entry.getValue());
 } //The fourth
 System.out.println("traverse all values ​​through Map.values(), but cannot traverse keys");
 for (String v : map.values()) {
 System.out.println("value= " + v);
 }
 }
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