Using Map.put(String, Integer) in a loop

Question

I´ve got a short question. I am so despaired because of my problem. I just want to put different Keys with the same Value in my Map by using a loop. My main executes the function einfuegen() for multiple times. As in the following code block:

Woerterbuch woerterbuch2 = new Woerterbuch2();
for (Medium m : medienliste) {
    for (String s : m.getWorte()) {
        woerterbuch2.einfuegen(s);
    }
}

By the way I have tested all the loops and assignments of the variables.

Now einfuegen() should put all the the Strings s in the Map. See the following code block:

public class Woerterbuch2 implements Woerterbuch{

    HashMap<String, Integer> liste = new HashMap<>();

    public void einfuegen(String word) {
        // I have deleted all the previous unimportant code
        liste.put(word, 1);
    }
}

My map only contains one entry, although the function einfuegen() is running for more than one time and there are more than one different String that is assigned to word. Normally my map should contain more than 50 different words, because einfuegen() is executed for more than 50 times.

My assumption is that Java overwrites the connection from 1 to word because 1 is always the same instance of Integer. If I´m right I still don´t know how to fix it.

Thanks for your help. I am really looking forward to it =)

What's the purpose of your code? Are you looking to count the number of times a word appears in a book? Assuming that's the case your einfugen method just adds an entry of 1 each time for word, whereas what you want to do is increment it (+1) if it already exists in your map, and if not add a 1 to it. — mohammedkhan
– mohammedkhan, Commented Dec 20, 2016 at 17:06
you should really create the instance of the hashmap in a constructor of the Woerterbuch2 class — RAZ_Muh_Taz
– RAZ_Muh_Taz, Commented Dec 20, 2016 at 17:11
After your edit, there is nothing recognizable that could exhibit the described behavior. Create a single program that reproduces the behavior without the need for code you haven’t shown us. This is called minimal reproducible example. — Holger
– Holger, Commented Dec 20, 2016 at 17:26

pringi · Accepted Answer · 2016-12-20 16:51:48Z

1

You are always creating the Map in einfuegen. This is the problem. Declare Map liste as an instance variable.

Example:

Class X{

private Map<String, Integer> liste = new HashMap<>();


Woerterbuch woerterbuch2 = new Woerterbuch2();
for (Medium m : medienliste) {
    for (String s : m.getWorte()) {
        woerterbuch2.einfuegen(s);
    }
}

public void einfuegen(String word) {
    // I have deleted all the previous unimportant code

    liste.put(word, 1);
}
}

answered Dec 20, 2016 at 16:51

pringi

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7 Comments

patrickkr Over a year ago

In my code I declared the HashMap as an instance variable.

ᴘᴀɴᴀʏɪᴏᴛɪs Over a year ago

@patrickkr By doing this Map<String, Integer> liste = new HashMap<>(); you are creating a new Map each time, that's why it always has only one entry in it.

patrickkr Over a year ago

Sorry for that mistake. Wanted to make the code shorter. But my code still dont works

patrickkr Over a year ago

public class Woerterbuch2 implements Woerterbuch{ HashMap<String, Integer> liste = new HashMap<>();

patrickkr Over a year ago

My class starts like this

|

Nilu · Accepted Answer · 2016-12-20 18:12:21Z

It doesn't matter if you have contant value for all your keys. But it matters if you are giving constant key.In case all the keys are same a single entry will be made .Debug your code to make sure that the Keys are unique.

1) Print the values in m.getWorte() to check that all keys sent are unique.

Have a look at Example Code

HashMap<String, Integer> myMap = new HashMap<>();
        myMap.put("s", 1);
        myMap.put("r", 1);
        myMap.put("m", 1);
        System.out.println(myMap); // This prints {r=1, s=1, m=1}

HashMap<String, Integer> myMap1 = new HashMap<>();
    myMap1.put("s", 1);
    myMap1.put("s", 2);
    myMap1.put("s", 3);
    System.out.println(myMap1); // This prints {s=3}

i.e entries are made in hashmap irrespective of values being constant and entries are ignored in hashmap if keys are same irrespective of different values

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