About the example operation of HashMap in java

HashMap introduction:

1. Store data in (key, value) pairs.

2. Duplicate keys are not allowed, but duplicate values ​​are allowed.

3. Not synchronized (multiple threads can access at the same time)

Recommended related video tutorials: java online learning

Example demonstrations are as follows:

1. Add

HashMap<String, String> hash_map = new HashMap<String, String>(); 
 
hash_map.put( "名字" , "anny" );
hash_map.put( "性别" , "女" );
hash_map.put( "年龄" , "20" );

2. Delete

HashMap<String, String> hash_map = new HashMap<String, String>(); 
 
hash_map.remove( "名字" );

3. Traverse

General performance:

HashMap<String, String> hash_map = new HashMap<String, String>(); 
 
hash_map.put( "名字" , "anny" );
hash_map.put( "性别" , "女" );
hash_map.put( "年龄" , "20" );

for(String key:hash_map.keySet())
{
  System.out.println("Key: "+key+" Value: "+hash_map.get(key));
}

Use the iterator() method of the Collection class to traverse the collection (good performance)

HashMap<String, String> hash_map = new HashMap<String, String>(); 
 
hash_map.put( "名字" , "anny" );
hash_map.put( "性别" , "女" );
hash_map.put( "年龄" , "20" );

Collection cl = hash_map.values();
Iterator itr = cl.iterator();
while (itr.hasNext()) {
    System.out.println(itr.next());
}

This article comes from the java entry program column to introduce you to some example operations about HashMap. Hope it helps everyone.

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