Converting Python into Java and facing some issues

Question

I'm converting the following Python Code into Java code as follows:

import random
howMany = random.randint(0,1000)
stats = {}
for i in range(howMany):
value = random.randint(0,500)
stats.setdefault(value,0)
stats[value]+=1
for item in stats:
if stats[item] > 1:
    print item

Here is the Java code I have written so far :

import java.util.Random;
import java.util.*;

public class PythonToJava 
{
    public static void main(String[] args) 
    {
        Random rm = new Random();
        int i = rm.nextInt(1000);
        HashMap<Integer,Integer> stats = new HashMap<Integer,Integer>();
        System.out.println("Random Number Generated is: " + i);
        for (int j = 0; j<i; j++)
        {
            int value = rm.nextInt(500);
            System.out.println("The value of VALUE is " + value);
            DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>();
            defaultvalue.put(value,0);
        }
    }
}

public class DefaultingMap<Integer, Integer> implements Map<Integer, Integer>
{
    private final Map<Integer, Integer> map;
    private final Integer defaultValue;
    public DefaultingMap(Map<Integer, Integer> map, Integer defaultValue)
    {
        this.map = map;
        this.defaultValue = defaultValue;
    }

    @Override public Integer get(Object key)
    {
        Integer ret = map.get(key);
        if (ret == null)
        {
            ret = defaultValue;
        }
        return ret;
    }

    @Override public int size()
    {
        return map.size();
    }
    // etc
}

But getting error at the following line:

Java Code:

DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>(); Error is : The constructor DefaultingMap() is undefined

and at public class DefaultingMap<Integer, Integer> implements Map<Integer, Integer>

Error is : Multiple markers at this line
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.remove(Object)
    - The type parameter Integer is hiding the type Integer
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.put(Integer, Integer)
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.keySet()
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.values()
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.containsKey(Object)
    - The type parameter Integer is hiding the type Integer
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.containsValue(Object)
    - Duplicate type parameter Integer
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.entrySet()
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.putAll(Map<? extends Integer,? extends Integer>)
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.isEmpty()
    - The type DefaultingMap<Integer,Integer> must implement the inherited abstract method 
     Map<Integer,Integer>.clear()

Can anyone explain why?

Basically I'm trying to set a default value somehow just like setdefault thing works in python. I would appreciate if someone can help me here.

DefaultingMap does not appear to be a part of the standard JDK. You may need to add additional libraries or simply use another class. — ApproachingDarknessFish
– ApproachingDarknessFish, Commented May 9, 2013 at 4:38
Is DefaultingMap in the same file as PythonToJava? You cannot define two public classes in the same file. — BevynQ
– BevynQ, Commented May 9, 2013 at 4:45
Also note that Python's randint(0,1000) equates to Java nextInt(1001), and same with the 500. Java's range is exclusive, Pythons is inclusive. — Lee Daniel Crocker
– Lee Daniel Crocker, Commented May 9, 2013 at 5:03

asifsid88 · Accepted Answer · 2013-05-09 05:04:37Z

2

What I see is You have parameterized constructor in DefaultingMap and default constructor is missing. Kindly Add default constructor

public DefaultingMap()
{
  // do your things
}

Otherwise change this call

DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>();
defaultvalue.put(value,0);

to this

DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>(value,0);

UPDATED
It is clear that you need to override all the methods from the MAP you have just overriden few. Kindly over-ride all the methods. Then this will resolve your issue
Following methods to over-ride

remove
put
keySet
values
containsKey
containsValue
entrySet
putAll
isEmpty

Refer Method Summary Section to see the methods to override

SUGGESTION If you do not wish to over-ride all the methods from MAP (as its really a pain) then rather than implements MAP you can have extends HashMap. With this you just have to over-ride the methods which you would like to. As in your case get and size

edited May 9, 2013 at 5:04

answered May 9, 2013 at 4:53

asifsid88

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8 Comments

Tan Over a year ago

Mentioning public DefaultingMap() { // do your things } did work but the second error still persists which is "Multiple Markers at this line.

asifsid88 Over a year ago

Can you tell us what is the other errors? Firstly, separate both the class into different files (As only one public class is permitted per file)

asifsid88 Over a year ago

It is clear that you need to override all the methods from the MAP you have just overriden few. Kindly over-ride all the methods. Then this will resolve your issue

Tan Over a year ago

Not sure which methods I need to override again. Could you please mention it here?

Tan Over a year ago

Thanks for your answer, I would rather extend HashMap here and after doing that also nothing changed. What could be the reason? Here is what I changed: class DefaultingMap<Integer, Integer> extends HashMap<Integer, Integer>

|

BevynQ · Accepted Answer · 2013-05-09 05:14:46Z

i modified

DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>();

to

DefaultingMap<Integer,Integer> defaultvalue = new DefaultingMap<Integer,Integer>(new HashMap<Integer, Integer>(),0);

Also

public class DefaultingMap<Integer, Integer> implements Map<Integer, Integer>
{
    private final Map<Integer, Integer> map;
    private final Integer defaultValue;

    public DefaultingMap(Map<Integer, Integer> map, Integer defaultValue)
    {
        this.map = map;
        this.defaultValue = defaultValue;
    }

    @Override public Integer get(Object key)
    {
        Integer ret = map.get(key);
        if (ret == null)
        {
            ret = defaultValue;
        }
        return ret;
    }

became

class DefaultingMap<K, V> implements Map<K,V>{ //remove public and use proper generic parameters

   private final Map<K, V> map; // is now generic
   private final V defaultValue; // must be of type V

   public DefaultingMap(Map<K, V> map, V defaultValue) throws IllegalArgumentException
   {
   /* because we have defined this constructor DefaultingMap() will need to be 
      defined if we need/want it. */
       if (map == null){
           throw new IllegalArgumentException("provided map cannot be null");
       }
       this.map = map;
       this.defaultValue = defaultValue;
   }

   public V get(Object key){

       V ret = map.get(key);
       if (ret == null){
           ret = defaultValue;
       }
       return ret;
   }

You need to implement all the methods in the Map interface do them this way if you are unsure

   @Override
   public V put(K key, V value) {
       return map.put(key,value); // delegate to map
   }

that worked for me.

Hi @BevynQ , Thanks for your answer. Could you please update your code for extending a class HashMap instead? I'm preferring to extend a class instead of overriding all the methods of Interface.

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