forEach loop Java 8 for Map entry set

Question

I'm trying to convert old conventional for each loop till java7 to java8's for each loop for a map entry set but I'm getting an error. Here's the code I'm trying to convert:

for (Map.Entry<String, String> entry : map.entrySet()) {
        System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
    }

Here's the changes I have done:

map.forEach( Map.Entry<String, String> entry -> {
       System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());

   }); 

I tried doing this as well :

Map.Entry<String, String> entry;
   map.forEach(entry -> {
       System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());

   });

But still facing error. The error I'm getting for this is : Lambda expression's signature does not match the signature of the functional interface method accept(String, String)

Answer 1

Read the javadoc: Map<K, V>.forEach() expects a BiConsumer<? super K,? super V> as argument, and the signature of the BiConsumer<T, U> abstract method is accept(T t, U u).

So you should pass it a lambda expression that takes two inputs as argument: the key and the value:

map.forEach((key, value) -> {
    System.out.println("Key : " + key + " Value : " + value);
});

Your code would work if you called forEach() on the entry set of the map, not on the map itself:

map.entrySet().forEach(entry -> {
    System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue());
});