Printing HashMap In Java

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I have a HashMap:

private HashMap<TypeKey, TypeValue> example = new HashMap<TypeKey, TypeValue>();

Now I would like to run through all the values and print them.

I wrote this:

for (TypeValue name : this.example.keySet()) {
    System.out.println(name);
}

It doesn't seem to work.

What is the problem?

EDIT: Another question: Is this collection zero based? I mean if it has 1 key and value will the size be 0 or 1?

keySet() only returns a set of keys from your hashmap, you should iterate this key set and the get the value from the hashmap using these keys.

In your example, the type of the hashmap's key is TypeKey, but you specified TypeValue in your generic for-loop, so it cannot be compiled. You should change it to :

for (TypeKey name: example.keySet()){
            String key = name.toString();
            String value = example.get(name).toString();  
            System.out.println(key + " " + value);  
} 

Update for Java8:

 example.entrySet().forEach(entry->{
    System.out.println(entry.getKey() + " " + entry.getValue());  
 });

If you don't require to print key value and just need the hashmap value, you can use others' suggestions.

Another question: Is this collection is zero base? I mean if it has 1 key and value will it size be 0 or 1?

The collection returned from keySet() is a Set.You cannot get the value from a Set using an index, so it is not a question of whether it is zero-based or one-based. If your hashmap has one key, the keySet() returned will have one entry inside, and its size will be 1.

Printing a java map Map<String, Object> - How?, Printing a java map Map<String, Object> - How? [duplicate] · java hashmap. This question already has answers here: How do I efficiently iterate  How to print the elements of a HashMap in Java? Java Object Oriented Programming Programming A HashMap is a subclass of AbstractMap class and it is used to store key & value pairs .

A simple way to see the key value pairs:

Map<String, Integer> map = new HashMap<>();
map.put("a", 1);
map.put("b", 2);
System.out.println(Arrays.asList(map)); // method 1
System.out.println(Collections.singletonList(map)); // method 2

Both method 1 and method 2 output this:

[{b=2, a=1}]

Print out all keys and values from a Map in Java, import java. util. Iterator; import java. util. class MapUtil. { // Program to print all keys present in the Map using keySet() in Java. public static void main (String[] args) { Map<Integer, String> map = new HashMap<>(); map. put(1, "One"); map. // 1. using Iterator. Iterator<Integer> itr = map. keySet(). iterator(); HashMap<K,V> HM = new HashMap<>(); //empty System.out.println(HM); //prints key value pairs enclosed in {} This works because the toString()method is already over-ridden in the AbstractMap class which is extended by the HashMap Class More information from the documentation . Returns a string representation of this map.

Assuming you have a Map<KeyType, ValueType>, you can print it like this:

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

How to print the elements of a HashMap in Java?, A HashMap is a subclass of AbstractMap class and it is used to store key & value pairs. Each key is mapped to a single value in the map and  in hashmap java java java 10 java 10 tutorial java example java map java tutorial Printing HashMap In Java published on July 21, 2018 Overview In this tutorial, we show you how to print out all keys and values in Map (HashMap) in Java 10.

To print both key and value, use the following:

for (Object objectName : example.keySet()) {
   System.out.println(objectName);
   System.out.println(example.get(objectName));
 }

How to print Map in Java 10, In this tutorial, we show you how to print out all keys and values in Map (​HashMap) in Java 10. now how can i print the contents of an object? coz the thing is, it retrieves results and places it in the object which then puts it in the hashmap. i can now print those in the hashmap for checking purposes, but how to do that in object without generating this "java.lang.Object@defa1a" ? thanks

Java Print HashMap Example, This example shows how to print HashMap in Java. The example also shows how to print all keys, all values, and all key-value pairs of  HashMap is a part of Java’s collection since Java 1.2. It provides the basic implementation of the Map interface of Java. It stores the data in (Key, Value) pairs. To access a value one must know its key. HashMap is known as HashMap because it uses a technique called Hashing. Hashing is a technique of converting a large String to small String

Printing a Hashmap (Beginning Java forum at Coderanch), In tracing, i would like to know the contents of the hashmap and in doing so, i would like to print its contents. Since i am new to java, i don't know  Java HashMap. You learned from the previous chapter, that Arrays store items as an ordered collection, and you have to access them with an index number (int type). A HashMap however, store items in "key/value" pairs, and you can access them by an index of another type (e.g. a String). One object is used as a key (index) to another object (value).

How to iterate any Map in Java, Since all maps in Java implement Map interface, following techniques will work for any map implementation (HashMap, TreeMap, LinkedHashMap, Hashtable,  HashMap is a Map based collection class that is used for storing Key & value pairs, it is denoted as HashMap<Key, Value> or HashMap<K, V>. This class makes no guarantees as to the order of the map. It is similar to the Hashtable class except that it is unsynchronized and permits nulls (null values and null key).

Traverse through a HashMap in Java, Adding mappings to HashMap. hm.put( "GeeksforGeeks" , 54 );. hm.put( "A computer portal" , 80 );. hm.put( "For geeks" , 82 );. // Printing the HashMap. 4. Java 8 – Stream.forEach() We can use loop through the keySet and values by using Stream.forEach() method that can print each element of the stream. 5. Using toString() For displaying all keys or values present in the map, we can simply print the string representation of keySet() and values() respectively.

Comments
  • I recommend you become familiar with Java's documentation (it will answer many of your questions). For example, this is the documentation for Map's size() method: "Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE."
  • Your code is looking for Values in Keys - which is not correct. Either look for key in Keys or value in Values
  • If it has 1 key / value it will ofcourse have size 1. But this does not have anything to do with zero-based indexing.
  • This is a good question. But there is an answer here provided here that can do this in one line, if you see Mingfei's solution.
  • Or better yet: for (Map.Entry<String, String> entry : map.entrySet()) { ... }
  • Just do as: System.out.println(map);, output: {b=2, a=1}
  • Yeah... one more similar output: System.out.println(map.toString());
  • @yoapps beware of NPE in this case. That's why I avoid the .toString when possible.
  • Thats true. the NPE always lurks in such short cuts. I only wanted to show a similar out put.. I think especially when you're debugging to a log/console and you just wana peek into a map whose data you know isnt null. this is a quick fire! But if its code checking from scratch... then you're right, its tricky and in good programming context, it should be avoided!
  • You are missing another bracket before the semi colon on the 3rd line.
  • this looks to be the best answer from the ones above.
  • While this code may solve the question, including an explanation of how and why this solves the problem would really help to improve the quality of your post, and probably result in more up-votes. Remember that you are answering the question for readers in the future, not just the person asking now. Please edit your answer to add explanation, and give an indication of what limitations and assumptions apply.