What is the easiest way to iterate over all the key/value pairs of a java.util.Map in Java 5 and higher?

Question

What is the easiest way to iterate over all the key/value pairs of a java.util.Map in Java 5 and higher?

Answer 1

Assuming K is your key type and V is your value type:

for (Map.Entry<K,V> entry : map.entrySet()) {
  K key = entry.getKey();
  V value = entry.getValue();
  // do stuff
}

This version works with every Java version that supports generic (i.e. Java 5 and up).

Java 10 simplified that by letting variable types be inferred using var:

for (var entry : map.entrySet()) {
  var key = entry.getKey();
  var value = entry.getValue();
  // do stuff
}

While the previous two options are basically equivalent at the bytecode level, Java 8 also introduced forEach which uses lambdas^* and works slightly difference. It invokes the lambda for each entry, which might add some overhead of those calls, if it's not optimized away:

map.forEach((k, v) -> { 
  // do stuff 
});

^{* technically the BiConsumer can also be implemented using a normal class, but it's intended for and mostly used with lambdas.}