Question

Use Java language

You may assume that you always map strings to integers, and therefore you need not worry about using generics.

Here are the methods that your map must implement.

void put (String key, Integer value);

insert this key-value pair into the map under the following rules:

If key already exists in the map, change its value to value, overwriting what was there

If key is not already there, insert this key-value pair into the map.

boolean containsKey(String key);

returns true iff key already exists in the map.

boolean containsValue(Integer value);

returns true iff value appears in the map. (N.B. Since the values need not be unique, this

doesn’t necessarily tell you anything interesting.)

boolean remove (Object key);

If key is in the map, remove it. (This is a little bit tricky).

Integer get(String key);

If key is in the map, return the associated value.

If key is NOT in the map, return null.

Set<Pair> entrySet();

Returns a Set of all pairs in the map.

List<Integer> values();

Returns a list of all of the associated values in the map.

Set<String> keySet();

Returns a set of all keys in the map.

int size();

returns the number of elements in the map

boolean isEmpty();

returns true iff the number of elements in the map is 0.

You will use a hash table as the underlying structure.

The declaration for the private data member should be:

private ArrayList<LinkedList<Pair>> theTable;

Pair should be an inner static class with the following methods.

Pair(String str, Integer value);

Constructs a pair

String getKey();

Returns the key

Integer getValue();

Returns the value

Integer setValue(Integer value);

Changes the value to a new value and returns the old value.

As always, your code must be heavily commented and documented.

Answer 1

SOLUTION

import java.util.HashMap;

import java.util.LinkedList;

import java.util.List;

import java.util.Map.Entry;

import java.util.Set;

public class HashMapMethods {

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

void put(String key, Integer value) {

if (!map.containsKey(key)) {

map.put(key, value);// if Key is not already present then Store the

// key-value pair

} else {

map.put(value.toString(), value);

// Else Stores into the Value

}

}

boolean containsKey(String key) {

if (map.containsKey(key))// Check if the key is already exist or not.

return true;

else

return false;

}

boolean containsValue(Integer value) {

if (map.containsValue(value))// Check if the value is already exist or

// not.

return true;

else

return false;

}

boolean remove(Object key) {

if (map.containsKey(key)) {

map.remove(key);

return true;

} else

return false;

}

Integer get(String key)

{

if(map.containsKey(key))

return map.get(key);

else

return null;

}

Set<Entry<String, Integer>> entrySet()

{

return map.entrySet();

}

List<Integer> values()

{

LinkedList<Integer>list=new LinkedList<Integer>();

list.addAll(map.values());

return list;

}

Set<String> keySet()

{

return map.keySet();

}

int size()

{

return map.size();

}

boolean isEmpty()

{

return map.isEmpty();

}

public static void main(String[] args) {

HashMapMethods obj = new HashMapMethods();

obj.map.put("Babu", 101);

obj.map.put("Ganesh", 102);

obj.map.put("Suresh", 103);

obj.map.put("Mahesh", 104);

obj.map.put("MAdhu", 105);

// Calling First Method

obj.put("Babu", 101);

// calling second Method

obj.containsKey("Babu");

// Calling Third Method

obj.containsValue(103);

//Calling Fourth Method Remove Key

System.out.println("Removed Key Successfully "+obj.remove("MAdhu"));

//Calling the Fifth Method

System.out.println("The value of the Key is : "+obj.get("Suresh"));

//Calling sixth Method

System.out.println("The Set of Key value pairs are: "+obj.entrySet());

//Calling the Seventh Method

System.out.println("The List of Value are: "+obj.values());

//Calling the Eight Method

System.out.println("The Set of Keys are: "+obj.keySet());

//Calling the 9th Method

System.out.println("The Size of the HashMAp is: "+obj.size());

//Calling 10th Method

System.out.println(" Empty or Not? "+obj.isEmpty());

}

}

********************************************************************************************************************************

Sample Output

Removed Key Successfully true

The value of the Key is : 103

The Set of Key value pairs are: [Suresh=103, Mahesh=104, 101=101, Babu=101, Ganesh=102]

The List of Value are: [103, 104, 101, 101, 102]

The Set of Keys are: [Suresh, Mahesh, 101, Babu, Ganesh]

The Size of the HashMAp is: 5

Empty or Not? false