How to iterate over all key-value pairs in a Map…

There are several ways:

Using entrySet(): The most common and efficient way. It returns a set of Map.Entry objects, which can then be iterated over.

// Example of using entrySet()
Map<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    String key = entry.getKey();
    Integer value = entry.getValue();
    // Process key and value
}

Using keySet() to get keys and then calling get(): Less efficient, as it performs an additional lookup for each key.

// Example of using keySet()
Map<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);

for (String key : map.keySet()) {
    Integer value = map.get(key);
    // Process key and value
}

Using forEach() with lambda expression (Java 8+): A convenient and concise way.

// Example of using forEach()
Map<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);

map.forEach((key, value) -> {
    // Process key and value
});

Using an iterator with entrySet(): A classic iteration method.

// Example of using iterator with entrySet()
Map<String, Integer> map = new HashMap<>();
map.put("A", 1);
map.put("B", 2);

Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator();
while (iterator.hasNext()) {
    Map.Entry<String, Integer> entry = iterator.next();
    String key = entry.getKey();
    Integer value = entry.getValue();
    // Process key and value
}

It is recommended to use entrySet() or forEach(), as they are the most efficient. The choice between them depends on coding style and backward compatibility requirements (for Java 8+).

How to iterate over all key-value pairs in a Map?