Summary of java List loop and Map loop

Summary of java List cycle and Map cycle

I made a summary of list and map. Without any technical content, I just reviewed api.

The test environment is under junit4. If you do not write one main method by yourself, it will be the same.

The first is the three cycles of List:

   @Test 
public void ForListTest() { 
  List<String> list = new ArrayList<String>(); 
  list.add("1"); 
  list.add("2"); 
  list.add("3"); 
  list.add("4"); 
  list.add("5"); 
 
  //  The iterator loop does not need to know the size and type of the collection, the best choice  
  for (@SuppressWarnings("rawtypes") 
  Iterator iterator = list.iterator(); iterator.hasNext();) { 
    String list = (String) iterator.next(); 
    System.out.println("01)Iterator for : ===============" + list); 
  } 
 
  // foreach compared for You don't need to know the length of the set  
  for (String list : list) { 
    System.out.println("02)foreach:=================" + list); 
  } 
 
  // for Loops both need to know the size of the set and need to be ordered  
  for (int i = 0; i < list.size(); i++) { 
    System.out.println("03)for==================" + list.get(i)); 
  } 
} 

Then there are the four cycles of Map:

   @Test 
public void ForMapTest() { 
  Map<String, String> map = new HashMap<String, String>(); 
  map.put("01", "1"); 
  map.put("02", "2"); 
  map.put("03", "3"); 
  map.put("04", "4"); 
  map.put("05", "5"); 
  Set<String> keySet = map.keySet(); 
  //1.keyset the foreach methods  
  for (String key : keySet) { 
    System.out.println("1)keyset:" + "key:" + key + " value:" 
        + map.get(key)); 
  } 
 
  Set<Entry<String, String>> entrySet = map.entrySet(); 
  //2.entryset Iterative approach  
  for (@SuppressWarnings("rawtypes") 
  Iterator iterator = entrySet.iterator(); iterator.hasNext();) { 
    @SuppressWarnings("unchecked") 
    Entry<String, String> entry = (Entry<String, String>) iterator 
        .next(); 
    System.out.println("02)entrySet,iterator: key:" + entry.getKey() 
        + " value:" + entry.getValue()); 
  } 
 
  //3. Recommended, maximum capacity  
  for (Entry<String, String> entry : entrySet) { 
    System.out.println("03)entrySet,foreach:key:" + entry.getKey() 
        + " value:" + entry.getValue()); 
  } 
 
  Collection<String> values = map.values(); 
  //4. Only loop out value The method of  
  for (String value : values) { 
    System.out.println("04)values,just for values,value:" + value); 
  } 
 
} 

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