Java: How to Iterate Through a Map?

There are multiple ways to iterate through a Java Map. Assuming the following map declaration:

Map<String,Object> m = new HashMap<String,Object>(); 

Here are the mutliple ways to iterate it.

Iterate on Keys and Values

// With an Iterator (with Generics) Iterator<Entry<String, Object>> iterator = m.entrySet().iterator(); while ( iterator.hasNext() ) { Entry<String, Object> item = iterator.next(); System.out.println(item.getKey() + " - " + item.getValue()); } // Without an Iterator (without Generics) Iterator iterator2 = m.entrySet().iterator(); while ( iterator2.hasNext() ) { Entry item = (Entry) iterator.next(); System.out.println(item.getKey() + " - " + item.getValue()); } // Using For Each (with Generics) for ( Entry<String, Object> item : m.entrySet() ) { System.out.println(item.getKey() + " - " + item.getValue()); } // Using For Each (without Generics) for ( Entry item : m.entrySet() ) { System.out.println(item.getKey() + " - " + item.getValue()); } // Inefficient (fetching value from key) for ( String key : m.keySet() ) { System.out.println(key + " - " + m.get(key)); }

Iterate on Keys Only

for ( String key : m.keySet() ) { System.out.println(key); }

Iterate on Values Only

for ( Object value : m.values() ) { System.out.println(value); }