Chapter 16, Problem 17PP

Program Plan Intro

To implement a hash table that marks the removed element with an “inactive” element

Program plan:

• In a file “HashSet.java”, import necessary package, and create a class “HashSet”,
  • Declare the array of “Object” type.
  • Declare the necessary variable.
  • Declare the static variable.
  • Define the constructor to create a hash table.
    • Create an array and set the current size to “0”.
  • Define the method “toString()” that returns the string representation of array.
  • Define the method “contains()”,
    • Assign the hash code.
    • Create a loop for probing sequence,
      • Check the condition,
        • If it is true, returns true.
      • Check whether it contains null value,
        • If it is true, returns false.
        • • Create a loop for second probing sequence,
            • Check the condition,
              • If it is true, returns true.
            • Check whether it contains null value,
              • If it is true, returns false.
          • Returns false.
  • Define the method “getHashCode()”,
    • Assign the hash code.
    • Check whether the value is less than “0”,
      • If it is true, assign the negative value.
        • • Update the hash value.
          • Return the hash code.
  • Define the method “add()”
    • Check whether there is a room before probing,
      • If it is true, call the method “resizeTable()()”.
        • • Assign the hash code returned from the method “getHashCode()”.
          • Create a loop to follow probing sequence,
            • Check whether the bucket has either null value or INACTIVE element,
              • If it is true, assign the object properties.
              • Increment the size.
              • Returns true.
            • Otherwise, check another condition,
              • Returns false.
          • Execute a loop to wrap around to”0” to the value less than the hash code,
            • Check whether the bucket contains either null value or INACTIVE element,
              • If it is true, assign the object properties.
              • Increment the size.
            • Otherwise, Check the condition,
              • Returns false.
          • Returns true.
  • Define the method “remove()” to remove the object from the set,
    • Get the hash code.
    • Set the position to “-1”.
    • Create a loop,
      • Check the condition,
        • If it is true, assign the hash code to position.
        • • Create a loop,
            • Check the condition,
              • If it is true, set the new position.
          • Check whether the position value is “-1”,
            • If it is true, returns false.
          • If the item found, replace it with INACTIVE element.
          • Decrement the size.
          • Returns true.
  • Define the method “iterator()” that returns an iterator that traverses the elements of the set.
  • Define the method “size()” to return the size.
  • Define the method “resizeTable()”,
    • Create an object.
    • Copy the bucket to the object array.
    • Assign the value to the bucket.
    • Set the current size to “0”.
    • Create a loop,
      • Check the condition,
        • If it is true, call the method “add()”.
  • Create a class “HashSetIterator”,
    • Declare the variable to denote bucket index.
    • Define the constructor that creates a hash set iterator that points to the first element of the hash set.
    • Define the method “hasNext ()”,
      • Create a loop,
        • Check the condition,
        • • Returns true.
            • Returns false.
    • Define the method “next ()”,
      • Execute the statement without checking the condition,
        • Increment the index.
        • Check the condition,
        • • If it is true, create an object for “NoSuchElementException”.
            • Check whether the current bucket value contains null,
              • Return the value.
    • Define the method “remove()”,
      • Throw an exception “UnsupportedOperationException”.
• In a file “HashSetTest.java”, create a class “HashSetTest”,
  • Define the method “main()”,
    • Create an object for “HashSet”.
    • Add the name “Harry” into the set.
    • Add the name “Romeo” into the set.
    • Add the name “Susannah” into the set.
    • Add the name “Sarah” into the set.
    • Add the name “Adam” into the set.
    • Add the name “Larry” into the set.
    • Print the set.
    • Print the expected output.
    • Remove “Susannah” from the set.
    • Print the set and expected result.
    • Check whether “Adam” is in the set and print the result.
    • Print the expected result.