Question

Java Quadratic Probing Hash table HELP!

Complete the Map and Entry class provided in Map.java. Create a tester/driver class to show the Map class is working as intended.

• Methods/Constructor correctly completed (2pt)
  • This is the Map class methods
  • Map(), put(key, value), get(key), isEmpty(), makeEmpty()
• Private class correctly completed (2pt)
  • This is the Entry class methods
  • Add the methods that are required for this to work correctly when stored in the QuadraticProbingHashTable
• Tester class (1pt)
  • Show the methods of the Map class are working correctly

public class Map {
   public Map()
  
   public void put(KeyType key, ValueType val)
   public ValueType get(KeyType key)
   public boolean isEmpty()
   public void makeEmpty()
  
   private QuadraticProbingHashTable> items;
  
   private static class Entry
   {
       KeyType key;
       ValueType value;
       //appropriate constructions, etc.
   }
}

public class QuadraticProbingHashTable
{
/**
* Construct the hash table.
*/
public QuadraticProbingHashTable( )
{
this( DEFAULT_TABLE_SIZE );
}

/**
* Construct the hash table.
* @param size the approximate initial size.
*/
public QuadraticProbingHashTable( int size )
{
allocateArray( size );
doClear( );
}

/**
* Insert into the hash table. If the item is
* already present, do nothing.
* @param x the item to insert.
*/
public boolean insert( AnyType x )
{
// Insert x as active
int currentPos = findPos( x );
if( isActive( currentPos ) )
return false;

array[ currentPos ] = new HashEntry<>( x, true );
theSize++;

// Rehash; see Section 5.5
if( ++occupied > array.length / 2 )
rehash( );

return true;
}

/**
* Expand the hash table.
*/
private void rehash( )
{
HashEntry [ ] oldArray = array;

// Create a new double-sized, empty table
allocateArray( 2 * oldArray.length );
occupied = 0;
theSize = 0;

// Copy table over
for( HashEntry entry : oldArray )
if( entry != null && entry.isActive )
insert( entry.element );
}

/**
* Method that performs quadratic probing resolution.
* @param x the item to search for.
* @return the position where the search terminates.
*/
private int findPos( AnyType x )
{
int offset = 1;
int currentPos = myhash( x );

while( array[ currentPos ] != null &&
!array[ currentPos ].element.equals( x ) )
{
currentPos += offset; // Compute ith probe
offset += 2;
if( currentPos >= array.length )
currentPos -= array.length;
}

return currentPos;
}

/**
* Remove from the hash table.
* @param x the item to remove.
* @return true if item removed
*/
public boolean remove( AnyType x )
{
int currentPos = findPos( x );
if( isActive( currentPos ) )
{
array[ currentPos ].isActive = false;
theSize--;
return true;
}
else
return false;
}

/**
* Get current size.
* @return the size.
*/
public int size( )
{
return theSize;
}

/**
* Get length of internal table.
* @return the size.
*/
public int capacity( )
{
return array.length;
}

/**
* Find an item in the hash table.
* @param x the item to search for.
* @return the matching item.
*/
public boolean contains( AnyType x )
{
int currentPos = findPos( x );
return isActive( currentPos );
}
public AnyType get( AnyType x )
   {
       int currentPos = findPos( x );
       if( isActive( currentPos ))
           return array[currentPos].element;
       else
           return null;
}

/**
* Return true if currentPos exists and is active.
* @param currentPos the result of a call to findPos.
* @return true if currentPos is active.
*/
private boolean isActive( int currentPos )
{
return array[ currentPos ] != null && array[ currentPos ].isActive;
}

/**
* Make the hash table logically empty.
*/
public void makeEmpty( )
{
doClear( );
}

private void doClear( )
{
occupied = 0;
theSize = 0;
for( int i = 0; i < array.length; i++ )
array[ i ] = null;
}

private int myhash( AnyType x )
{
int hashVal = x.hashCode( );

hashVal %= array.length;
if( hashVal < 0 )
hashVal += array.length;

return hashVal;
}

private static class HashEntry
{
public AnyType element; // the element
public boolean isActive; // false if marked deleted

public HashEntry( AnyType e )
{
this( e, true );
}

public HashEntry( AnyType e, boolean i )
{
element = e;
isActive = i;
}
}

private static final int DEFAULT_TABLE_SIZE = 101;

private HashEntry [ ] array; // The array of elements
private int occupied; // The number of occupied cells
private int theSize; // Current size

/**
* Internal method to allocate array.
* @param arraySize the size of the array.
*/
private void allocateArray( int arraySize )
{
array = new HashEntry[ nextPrime( arraySize ) ];
}

/**
* Internal method to find a prime number at least as large as n.
* @param n the starting number (must be positive).
* @return a prime number larger than or equal to n.
*/
private static int nextPrime( int n )
{
if( n % 2 == 0 )
n++;

for( ; !isPrime( n ); n += 2 )
;

return n;
}

/**
* Internal method to test if a number is prime.
* Not an efficient algorithm.
* @param n the number to test.
* @return the result of the test.
*/
private static boolean isPrime( int n )
{
if( n == 2 || n == 3 )
return true;

if( n == 1 || n % 2 == 0 )
return false;

for( int i = 3; i * i <= n; i += 2 )
if( n % i == 0 )
return false;

return true;
}
}

Answer 1

when compiling the above code. we will get the errors as follows

1. Expected ";" for the constructor Map() and remaining classes

2.Accessing private class will give error as it belongs to only that particular class.

3.Paramteres are passing in isEmpty() and makeEmpty() whereas those two functions aren't assed any parameters in the main class.

Main.java:10: error: ';' expected
public Map()
^
Main.java:12: error: ';' expected
public void put(KeyType key, ValueType val)
^
Main.java:13: error: ';' expected
public ValueType get(KeyType key)
^
Main.java:14: error: ';' expected
public boolean isEmpty()
^
Main.java:15: error: ';' expected
public void makeEmpty()
^
Main.java:17: error: expected
private QuadraticProbingHashTable> items;
^
Main.java:17: error: expected
private QuadraticProbingHashTable> items;
^

Main.java:9: error: class Map is public, should be declared in a file named Map.java
public class Map {
^
Main.java:27: error: class QuadraticProbingHashTable is public, should be declared in a file named QuadraticProbingHashTable.java
public class QuadraticProbingHashTable
^
Main.java:12: error: cannot find symbol
public void put(KeyType key, ValueType val);
^
symbol: class KeyType
location: class Map
Main.java:12: error: cannot find symbol
public void put(KeyType key, ValueType val);
^
symbol: class ValueType
location: class Map
Main.java:13: error: cannot find symbol
public ValueType get(KeyType key);
^
symbol: class KeyType
location: class Map
Main.java:13: error: cannot find symbol
public ValueType get(KeyType key);
^
symbol: class ValueType
location: class Map
Main.java:52: error: cannot find symbol
public boolean insert( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:92: error: cannot find symbol
private int findPos( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:114: error: cannot find symbol
public boolean remove( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:150: error: cannot find symbol
public boolean contains( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:155: error: cannot find symbol
public AnyType get( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:155: error: cannot find symbol
public AnyType get( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:190: error: cannot find symbol
private int myhash( AnyType x )
^
symbol: class AnyType
location: class QuadraticProbingHashTable
Main.java:203: error: cannot find symbol
public AnyType element; // the element
^
symbol: class AnyType
location: class HashEntry
Main.java:206: error: cannot find symbol
public HashEntry( AnyType e )
^
symbol: class AnyType
location: class HashEntry
Main.java:211: error: cannot find symbol
public HashEntry( AnyType e, boolean i )
^
symbol: class AnyType
location: class HashEntry
Main.java:21: error: cannot find symbol
KeyType key;
^
symbol: class KeyType
location: class Entry
Main.java:22: error: cannot find symbol
ValueType value;
^
symbol: class ValueType
location: class Entry
Main.java:10: error: missing method body, or declare abstract
public Map();
^
Main.java:12: error: missing method body, or declare abstract
public void put(KeyType key, ValueType val);
^
Main.java:13: error: missing method body, or declare abstract
public ValueType get(KeyType key);
^
Main.java:14: error: missing method body, or declare abstract
public boolean isEmpty();
^
Main.java:15: error: missing method body, or declare abstract
public void makeEmpty();
^
Main.java:59: error: cannot infer type arguments for HashEntry
array[ currentPos ] = new HashEntry<>( x, true );
^
reason: cannot use '<>' with non-generic class HashEntry