How to print all values of specific Hashmap key

Question

Current Problem : I've build a HashMap to save and retrieve some key and values. but i'm not sure how to retrieve all values by a specific name (String). At the moment it's printing all the values from the Hashmap and that's not the thing that i want to achieve.

In the example below i'm using the following fields

Fields

String name
// Object Example

The HashMap

Map<String,Example> mapOfExampleObjects = new HashMap<String,Example>();

The for loop to retrieve the values from the hashmap by a certain key name

for(Map.Entry<String,Example> entry: mapOfExampleObjects.entrySet()){
                    if(mapOfExampleObjects.containsKey(name))
                    {
                    System.out.println(entry.getKey() + " " + entry.getValue());
                    }
                }

Current output

John + (Exampleobject)
Ian + (Exampleobject)
Ian + (Exampleobject)
Jalisha + (Exampleobject)

The Output that i want to achieve

Ian + (Exampleobject)
Ian + (Exampleobject)

Answer 1

Lars, your problem is this line:

            if(mapOfExampleObjects.containsKey(name))

Your mapOfExampleObjects will always contain the key 'Ian' every time you go through the loop. What you want is more like:

if( name.equals(entry.getKey()) )

Answer 2

You can extract the keySet of the map and manipulate it to select the entries you want:

class Example {

    final String name;

    Example(String name) {
        this.name = name;
    }

    public String toString() {
        return name;
    }
}

public void test() {
    // Sample data.
    Map<String, Example> mapOfExampleObjects = new HashMap<String, Example>();
    mapOfExampleObjects.put("John", new Example("John Smith"));
    mapOfExampleObjects.put("Ian", new Example("Ian Bloggs"));
    mapOfExampleObjects.put("Ian", new Example("Ian Smith"));
    mapOfExampleObjects.put("Jalisha", new Example("Jalisha Q"));
    // Using a Set you can extract many.
    Set<String> want = new HashSet<String>(Arrays.asList("Ian"));
    // Do the extract - Just keep the ones I want.
    Set<String> found = mapOfExampleObjects.keySet();
    found.retainAll(want);
    // Print them.
    for (String s : found) {
        System.out.println(mapOfExampleObjects.get(s));
    }
}

Note that this will still only print one Ian because a Map retains only one value against each key. You will need to use a different structure (perhaps Map<String,List<Example>> ) to retain multiple values against each key.