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 lt String  String gt  entry   map entrySet              System out println  Key       entry getKey       Value       entry getValue             Here s the changes I have done   map forEach  Map Entry lt String  String gt  entry - gt           System out println  Key       entry getKey       Value       entry getValue                I tried doing this as well    Map Entry lt String  String gt  entry     map forEach entry - gt           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

User · Answer

Maybe the best way to answer the questions like "which version is faster and which one shall I use?" is to look to the source code:

map.forEach() - from Map.java

default void forEach(BiConsumer<? super K, ? super V> action) {
    Objects.requireNonNull(action);
    for (Map.Entry<K, V> entry : entrySet()) {
        K k;
        V v;
        try {
            k = entry.getKey();
            v = entry.getValue();
        } catch(IllegalStateException ise) {
            // this usually means the entry is no longer in the map.
            throw new ConcurrentModificationException(ise);
        }
        action.accept(k, v);
    }
}

javadoc

map.entrySet().forEach() - from Iterable.java

default void forEach(Consumer<? super T> action) {
    Objects.requireNonNull(action);
    for (T t : this) {
        action.accept(t);
    }
}

javadoc

This immediately reveals that map.forEach() is also using Map.Entry internally. So I would not expect any performance benefit in using map.forEach() over the map.entrySet().forEach(). So in your case the answer really depends on your personal taste :)

For the complete list of differences please refer to the provided javadoc links. Happy coding!

User · Answer

You can use the following code for your requirement  map forEach  k v - gt System out println  Item       k     Count       v

User · Answer

Stream API  public void iterateStreamAPI Map lt String  Integer gt  map        map entrySet   stream   forEach e - gt  System out println e getKey        e getValue

User · Answer

String ss    quot Pawan kavita kiyansh Patidar Patidar quot       StringBuilder ress   new StringBuilder             Map lt Character  Integer gt  fre   ss chars   boxed                collect Collectors toMap k- gt Character valueOf  char  k intValue    k- gt 1 Integer  sum                 fre forEach  k  v  - gt  System out println  k    quot   quot    v              fre entrySet   forEach e - gt                 System out println e getKey      quot   quot    e getValue                   ress append String valueOf e getKey    e getValue                       fre forEach  k v - gt             System out println  quot Item    quot    k    quot  Count    quot    v           ress append String valueOf k  String valueOf v                     System out println ress toString

User · Answer

HashMap lt String Integer gt  hm   new HashMap      hm put  A  1    hm put  B  2    hm put  C  3    hm put  D  4     hm forEach  key value - gt        System out println  Key    key     value    value

User · Answer

Read the javadoc  Map lt K  V gt  forEach   expects a BiConsumer lt   super K   super V gt  as argument  and the signature of the BiConsumer lt T  U gt  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  - gt        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 - gt        System out println  Key       entry getKey       Value       entry getValue

[java] forEach loop Java 8 for Map entry set

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